Understanding Atoms and Elements: A Comprehensive Overview of Chapter 4 in Chemistry

hello everyone today we are going to start discussing chapter four which is all about atoms and elements and this

chapter is extremely important to really understanding the fundamentals of chemistry

so this lecture will cover the eight sections in chapter four that focuses on atoms and

elements and so first we're going to go to go ahead and start with elements and

symbols so a chemical symbol is a one or two letter

abbreviation used to represent an element and so let's look at some examples

number five on the periodic table is boron and this is represented as a capital b

we have the next atom over which is carbon number

six on the periodic table is represented as a capital c you have lead which is

uh down in the bottom on the right hand side of the periodic table this is represented as pb because of its greek

name plumbum but we know it as blood so the representation the two letter

abbreviation may or may not correlate to the name that we're used to so you will have a periodic table to to

utilize so you do not need to remember all of the one or two letter symbols for each of the elements on the periodic

table so a chemical symbol is a one or two letter representation for an element on

the periodic table so now let's go ahead and talk about the periodic table so section 4.2 is the

periodic table and in this section we are going to learn about uh the periodic table but

let's first learn some terminology so you have a group or a column i will be calling them columns

but you may hear it as a group and a group is a family of elements with

some similar pop properties a family of elements with similar properties

so the properties are similar within a column so for a group again we're looking at a

column and uh the way that you remember this is columns will build buildings up and down so it is vertical so a column

is a vertical representation on the periodic table and

the this family shares similar properties of one another that's a group we also have a period

and you will not refer hear me reference as group or period i like to use column rows a period is a row

on the periodic table and this is just a family of elements

in a row okay so it's a little bit different it's not grouped

as it's not grouped in the same way that a column is a period is a row of the periodic table and they don't

necessarily have similar properties but they are all within a row of one another and so again columns share properties

and rows are the way that the periodic table is set up so let's go ahead and look at how the periodic table is set up

this is the periodic table of elements that is from your textbook i'm going to go ahead and highlight it

in this tan color this is the periodic table and so when

we're looking at our periodic table our columns are up and down are horizontal excuse me vertical a

column is a vertical group and then we had our rows which is the horizontal group

so a row or a period and we either call this a column or a group

so remember the groups have the columns have the same chemical properties or similar chemical

properties and so uh lithium sodium potassium rubidium cesium and franzium all this first group

here on the periodic table all share similar properties of one another

because they're all in the same column the same is going to be true and we're looking over here on the right hand side

of the periodic table all of these in the very last column are also that i'm highlighting in yellow

are also going to share chemical properties uh the same similar chemical properties as one another

so let's go ahead and name everything on the periodic table you'll have the periodic table to use uh for all exams

and everything like that you do not need to memorize this so here is the different

groups of the periodic table and again they're uh a group by definition

is a column on the periodic table

and it's a family of elements so it's a group or a column i like column better

a family of elements that share chemi that share chemical properties

so the very first group that we have is group one or one a

and those are called the alkali metals second over we have uh column two a or

group two a and those are called the alkaline earth metals this is

uh 3b 4b 5b 6b7b 8b 9b

b 11 b and 12 b and these are all called the transition

metals in that periodic table over here in blue these uh 3a through 6a have no common names

they're just there's no common names then 7a are the halogens and those all share symbol

similar chemical properties and then last but not least that last row is called the noble gases

and those are always going to share the same chemical properties and then you'll see two rows down here

and the first is called the lanthanides and then the actinides

and this block and i'm going to go ahead and highlight this block in green since we haven't used green yet

the block that's underneath the periodic table is typically very uncommon we don't really focus on those two

rows necessarily in this class so the other thing that we want to know

about the periodic table is most elements on the periodic table are metals

and metals are shiny solids

and this is most elements on the periodic table so we'll have see some metals we'll also

see some non-metals and this is the group that typically the ones with no common names a lot of those happen to be

non-metals halogens and noble gases are also non-metals and these are not shiny

ductile um they're not shiny they tend to be ductile

and malleable these are core conductors of electricity and the last group on the periodic table

are the metalloids and these are not as common but there are these groups on the periodic table um and i'm going

to go ahead and highlight them in orange so the ones that are along this stair

step on the periodic table happen to be metalloids so those were those lie on

the periodic table and these are elements that exhibit both metal and non-metal properties

and so we will discuss all of this later on but those are just some more definitions

so we have our metals which happen to be shiny solids and those are most elements on the periodic table happen to be

metals you have your non-metals which are not shiny um they're ductile and they happen

to be more malleable they're poor conductors of electricity organic chemistry focuses a lot on the

non-metal portion of the periodic table and last but not least we have metalloids which are on the stair step

and those exhibit both metal and non-metal properties so they're not very common commonly used elements when they

are used they're very functional but they're not necessarily commonly used elements on the periodic table

so that's section 4.1 and 4.2 so let's go ahead and talk about section 4.3 next which is the atom

and this is again really important in understanding chemistry and understanding the

uh what's actually going on in chemical reaction so you have dalton's theory and his theory stated four different

things and the first is that all atoms all um everything all particles

are made up of atoms so that's the first thing that was said was that all particles are made up of

atoms the second thing that he said is all atoms of a given element all atoms of a given element

are the same as each other and different

from any other element so all carbon atoms are the same but they're always going to

be different than any boron atoms that's what we're saying there and so all atoms of a given element for example

boron are the same as each other so all boron atoms are the same as one another but they're all different than any other

element on the periodic table so no boron atom is like a carbon atom no boron atom is like a magnesium atom but

all boron atoms are the same atoms plus elements form compounds so two or more elements

form compounds so if you have a compound that means that you have two or more elements and

the last thing that was stated is that a chemical reaction reaction rxn a chemical reaction

involves rearrangement of atoms and that rearrangement can be a

separation of atoms it can be a combination of atoms it could be the atoms just simply rearranging but

something has to happen in order for a chemical reaction to proceed and so somehow though this atoms need to be

rearranged so dalton's theory was four different things all particles are made up of

atoms all atoms of a given element are the same as one another but different from any other element

two or more elements form compounds and a chemical reaction involves the rearrangement of atoms that's what was

stated so now let's go ahead and look at the electrical charge in an atom we still

haven't really defined what an atom is but we're now looking at the electrical charge

of an atom so inside the nucleus you have things called protons and those protons have a

positive charge outside the nucleus you have and this is not a correct representation

of the atom it's just showing that inside the nucleus you have protons so inside the nucleus

you have protons and protons again we're looking at the electrical charge of an atom inside the nucleus you have protons

and those have a positive charge one unit of positive charge and so that is a proton one unit of

inside of uh a proton is one unit of a positive charge and that's found inside the nucleus

you also have a neutron and i do not have that shown on this diagram which is no problem this is also

inside the nucleus this has no charge so it's not really going to influence the way that the

molecule is necessarily going to behave so a neutron is inside the nucleus and that has no charge so that is a neutron

and we'll talk about neutrons those again are inside the nucleus and those have no charge

and then last but not least we have outside the nucleus again my representation of the atom is

not correct we have the outside the nucleus you have an electron

and that is one unit of negative charge so outside that nucleus we have an electron and that has a negative charge

so we have a negative charge and a negative charge and a negative charge outside the nucleus inside the nucleus

you either have positive charge or no charge so that is the electrical charge of the atom again we still haven't

really talked about what that means but inside the nucleus we have protons and neutrons

and outside the nucleus we have an electron again we still haven't talked about uh what that means we will talk

about that later in this chapter we're just setting the stage of what is to come so let's go ahead and look at

the mass of an atom we're only going to be looking at the proton and the neutron so a proton

which has one unit of positive charge has a mass of again we're looking at the mass a proton

has a mass of 1.67 times 10 to the negative 24 grams an electron which is one unit of

negative charge has a mass of 9.11 times 10 to the negative 28 grams so we can see that both of these numbers

are very small but what we'll also notice is our mass of our proton

is much greater than the mass of our electron and that's because that negative number is smaller

um a proton has a mass of 1.67 times take 10 to the negative 24. and elect one single

electron has a mass of 9.11 times 10 to the negative 28. so these

units are or are typically difficult to work with because

again we don't want to have to constantly use these exponential factors in every single

calculation so what we can do is use an amu and an amu means an atomic mass unit and this is going to be helpful so we

have amu and that's abbreviated for an atomic mass unit and that's really helpful because this

allows for us to ignore or not really consider those exponents so when atomic

mass units allow us to use

the numerical values in calculations

without using the exponents because again those exponents when we need to start calculating things those

exponents are very large or excuse me very small um and so they can get quite uh quite

annoying to you so instead of actually using the mass of a proton and the mass of an electron we use this thing called

an atomic mass unit and that allows for individuals to actually carry out

calculations without having to take into account that exponent and the way that we calculate this

atomic mass unit is we need to have a standard we need to be able to compare everything so we use

carbon-12 it's just the standard that we use and what we're saying is for carbon-12

that has 6.02 times 10 to the 23rd atoms that's a lot of atoms taking into account the 12 protons

excuse me the six protons and the six electrons and the six neutrons so this is six protons

six neutrons you're not expected to know this yet in six electrons so we have six protons six neutrons and six electrons

when we add all of those up in 6.022 times 10 to the 23rd atoms that is going to equal

12 grams so 6.02 times 10 to the 23rd atoms of carbon will

atom will have six protons six neutrons and six electrons if we take the mass of all of those

atoms 6.02 times 10 to the 23rd atoms that will give us 12 grams of uh carbon so this is what we use

as our standard to compare

all other elements on the periodic table so again that way that of allows us to

not use those exponents because again those can get in the way of calculations and they can make um calculations to be

difficult so again we haven't really discussed but any of this means we are just laying the

groundwork so that that way we can discuss what all of this means um in future

material in this chapter as well as other lectures as well so let's go ahead and look at 4.21 together so 4.21

true or false that's what we're asking true or false one we want to ask or we're asking are

protons and electrons do those have opposite charges protons have a positive charge electrons

have a negative charge excuse me not an e electrons have a negative charge so yes those are

opposite charges and so what we're going to say is that this is a true statement because yes those are opposite charges

so question b is asking the nucleus contains most of the mass of an atom

so again we're looking in we want to think about what's going inside that nucleus protons and those have a

molecular mass of 1.67 times 10 to the negative 24 grams outside the nucleus we have our

electrons outside the nucleus we have 9.1 for every electron 9.11 times 10 to the negative 28 grams

and so inside the nucleus we have a much larger amount of material so again this statement is true

so let's go ahead and look at c and what we're asking is that electrons repel one another

we're asking ourselves is this statement true or is this statement false so you have one electron with a negative

charge and you have another electron with a negative charge and so think about this in terms of a magnet

opposites attract one another so these two electrons are absolutely going to repel one another so when you put a

magnet on the refrigerator it's attracted to the refrigerator when you hold two magnets of the same

pull towards one another they are harder to push together and that's because those electrons are

repelling one another so yes this is a true statement now let's look at

d and d is saying that protons are attracted to the

neutron protons are attracted to neutrons

so remember protons have a positive charge and neutrons are going to have an overall

zero charge there's no charge to a neutron so a positive charge is not going to be attracted or unattracted to

a net zero charge uh because they're not opposites of one another so this is a

false statement so uh again that's what's going on

inside and outside the nucleus of an atom so now let's talk about what actually

defines an atom is it the protons is it the neutrons or is it the electrons so this is section 4.4

the atomic number and the mass number so section 4.4 is all about the atomic number

and the mass number so your atomic number is the number of protons

this is really important your atomic number is the number of protons i'm going to highlight this in this bright

purple color your atomic number is the number of protons that you have it is not

the number of electrons so your atomic number is the number of protons and it's not necessarily the

number of electrons it can be but it's not necessarily the number of electrons so let's go ahead and look at for

example lithium lithium will have an atomic number of three that means that lithium is going

to have an atomic number of three that means lithium is going to have three protons

again we're not really thinking about the electrons at this point not yet but we will

the mass number uh let's let's look at carbon um carbon because we're going to talk about carbon's mass number so

carbon has an atomic number of six so carbon has an atomic number of six and so that means carbons

has six protons it may have six electrons it may not so the atomic number is what is uh the

number of protons and that determines the element on the periodic table now let's look at the mass number so

we've looked at the atomic number that's the number of protons your mass number

is the number of protons and neutrons again everything that's going on inside the

nucleus not outside the nucleus the number of protons and neutrons

so remember you find your protons and your neutrons in the nucleus

so we're not even talking about anything going on outside of the nucleus your mass number are the number of

protons and the number of neutrons so you'll see carbon 12. so what we can say is that we have

12 neutrons plus protons because that is the definition of the mass number

carbon is number six on the periodic table so you have the number of protons and so 12 minus six is equal to six so

you have six neutrons so inside the nucleus of a carbon atom you have six protons the number of

protons and so we find that by um the number on the periodic table carbon is number six the sixth element on the

periodic table so you have six protons inside the nucleus carbon has an atomic number of

excuse me a mass number of 12 and that is the mass number is equal to the number of neutrons and protons

so that is equal to six neutrons so you have six neutrons inside the nucleus as well

because remember by definition that mass number is the number of protons and neutrons and so that is this number here

and that's the number that we will find on the periodic 12.

so let's look at 4.3 together so 4.3 is zinc is a micro

mineral and it's needed to metabolize uh reactions and cells and dna synthesis it's used in the growth of bones t teeth

connective tissue and proper functioning of the immune system for an atom of zinc it has a mass number

of 68 so we have a mass number of 68. let me go ahead and fix that so that it's all blue

a mass number of 68 and so the question is asking us to determine the number of protons neutrons and electrons

so we have a mass number of 68 so let's just go ahead and write our 68 and zinc

that's the element that we're looking for on the periodic table it's two-letter abbreviation is zn

so you can find that on the periodic table you again you'll be able to use the periodic table on your exams and

everything so you should always have a periodic table available for you for your homework

what you'll find is that zinc is number 30 on the periodic table

so because zinc is number 30 on the periodic table we must have 30 protons because the atomic number

is your number of protons which is also the number of

the element on the periodic table so zinc is number 30 on the periodic

table so we're going to go ahead and write that our mass number

is the atomic number the number of protons plus the number of neutrons

from the mass number we can subtract out the number of protons and that will give us the number of

neutrons so our mass number of zinc happened to be 68 it happens to be 68 and we have 30

protons so that would leave us 38 neutrons 68 minus 30 will leave you 38 neutrons

and under normal circumstances not always but

under most circumstances the number of protons and the number of electrons are going to be the same and so if you have

30 protons you need to have 30 electrons and we will talk about when this is not true later on we're not talking about um

then when you have a varying number of protons and electrons yet we will get

there so as of now your number of protons and your number of electrons are the same let's think about why that is

i'm not going to use zinc as the example because again we have 30 and that's a lot to draw but let's go ahead and look

at hydrogen the most basic element on the periodic table

hydrogen hydrogen is number one on the periodic table it's the first element on the periodic table

therefore we know we have one proton right now we're not talking about elec uh neutrons we're just discussing why

neutral atoms have the same number of

protons and electrons so when you're looking at inside the

nucleus of a hydrogen atom you have one proton and so outside of the nucleus you have one electron so plus one inside the

nucleus minus one is equal to zero and so this is your overall charge

and elements on the periodic table are neutral meaning they have no charge so what's going on inside that nucleus you

have one positive charge has to also be going on outside of the nucleus so you have your plus one going on inside the

nucleus that's your proton and you have your minus one going on outside the nucleus is your electron and

again we haven't talked about any elements that have a charge yet we will get there in a different chapter so

zero is the overall charge for now what you're looking for zero is always going to be the overall charge i mean

that means again we want to think about this in terms of inside the nucleus and outside the nucleus

are the same that's not always going to be true um chemical reactions happen when there's

an imbalance of inside the nucleus and outside the nucleus but right now we're not talking about chemical reactions

we're only trying to understand how the atom is set up so let's go ahead and look at problem

4.31 here's a periodic table that you will be able to use so here's the periodic

table to use again i would strongly recommend having this for your homework and here is the sample question it's

asking you to complete the following table um for elements that are essential to

the body so we have zn which we just looked at that is going to be number 30 on the periodic table zinc right here

number 30 on the periodic table the name of the element is zinc it has an atomic number of 30 that's the

number of protons and you'll find that number up here where i'm highlighting currently

in blue that is the atomic number the mass number is 66 so that means that you have 30 protons and you have 30

electrons so therefore you must have 36 neutrons zinc

so we're looking for atomic number 12 so we're going to look for atomic number 12 on the periodic table this is magnesium

mg and so we're going to be looking at magnesium magnesium is atomic number 12. that must

mean that it has 12 protons and 12 electrons i have 12 neutrons so therefore i must have an mass number of

24. potassium is k on the periodic table so that has a one

letter symbol of k the atomic number of potassium is 19. so that must mean you have 19 protons

and 19 electrons we have 20 neutrons so therefore we have 39 as our mass number

we're looking for a number of protons which is going to be the same number as the atomic number of

16 and that is sulfur right here on the periodic table underneath oxygen sulfur

that is a chemical representation of s it has 16 protons so therefore it must have 16 electrons 16 elec protons plus

15 neutrons is going to give you a mass number of

31 and last but not least we have a mass number of 56 and a number of electrons

is 26. again we're only looking at neutral elements so the number of electrons have to equal the number of

protons for now so 26 protons so we're looking for 26 on the periodic table which is iron

chemical representation fe iron has an atomic number of 26 and it has a 26 protons and a mass

number of 56 so therefore it must have 30 neutrons so there is 4.32 which you'll also have

as your homework so i would definitely practice completing these tables and really understanding what each of those

mean now we're going to talk about isotopes isotopes is section 4.5

and isotopes is still what's going on inside the nucleus we haven't talked anything about what goes on outside the

nucleus so right now we're assuming outside the nucleus is uh

the same as inside the nucleus we have not talked about what happens when something goes on outside the nucleus

so isotopes and atomic mass remember your atomic mass is the number of protons

so an isotope is going to be a varying number of neutrons

a varying number of neutrons your atomic mass your number of protons that can never vary

for a specific element on the periodic table that is never going to change all lithium is atoms are always going to

have three protons that's not going to change there are special circumstances where it does we are not talking about

that in this class whatsoever so you can assume that the number of protons can never change

so when we're talking about an isotope we're still talking about what's going on inside the nucleus and that's going

to be a varying number of neutrons so let's go ahead and look at our hydrogen atom again

so for a hydrogen atom inside the nucleus you have one proton and outside the nucleus you have one electron so we

have one proton and we have one electron again we're talking about isotopes so we're not

talking about what's going on with the proton or the electron in a normal hydrogen atom you have zero neutrons

in a hydrogen atom you inside the nucleus you can still have one proton and again that is going to be your

atomic mass that is the definition of an element on the periodic table the proton count is never going to change

right now we're not looking at all what's going on outside the nucleus so we can still assume that we have one

electron and if we add one neutron into that nucleus we're adding no charge it has a zero charge

but what we're doing is we still have one proton and we have one electron

and now we have one neutron so again we're not adding there's no charge

change we're not adding any chemical charge the protons are positively charged the

electrons are negatively charged the neutrons are zero charged but now we have one neutron and so that

is going to change the mass of hydrogen but nothing else so when we have one neutron this is called deuterium

it doesn't change anything except for the mass of the element itself and so that is where you have one

neutron so now again let's look we're still looking at that hydrogen atom inside the

nucleus we have one proton because we're not looking at the atomic number outside the nucleus we can

assume we stop one electron because we have not discussed what happens when you have varying electron counts but inside

the nucleus now we have two neutrons so inside the nucleus we still have one proton

because again that cannot change we're still talking about the hydrogen atom outside the nucleus we still have one

electron because we haven't talked about electrons at all um so we can assume the number of protons is equal to the number

of electrons now inside the nucleus we have two neutrons

again this has a positive one charge the electron has a negative one charge and inside the nucleus we have two zero

charges so we're not changing the overall charge but this is called tritium

and that is still a hydrogen atom with two electrons uh excuse me with two neutrons

with two neutrons that is tritium so again you're not changing the chemical charge whatsoever but you are adding two

neutrons so isotopes make heavier

atoms but no other

change and isotopes exist for many elements on the periodic table not

all of them but many of them so when we're looking at elements on the periodic table we want to think about

our atomic mass not our atomic number our atomic mass how much does an atom weigh

the atomic mass and what this does is it takes into account

so the definition of atomic mass is how much an atom weighs and this takes into account

it takes into account each isotope and we're going to see an example of

this and the percent of each isotope

so what does this actually mean let's let it look at an example we're going to look at

magnesium magnesium has three three stable isotopes so let's go ahead and look at the

isotopes of magnesium we have magnesium 24 so we're going to

look at our proton count our electron count our mass number all of magnesium the isotopes and

magnesium our neutron count which has no charge the mass isotope

which we're going to call our atomic mass unit or amu so we don't have to use those exponents and last but not least

we're going to look at the percent abundance of each of these group so you have again we're looking at

magnesium magnesium has three isotopes it has magnesium 24.

and magnesium is number 12 on the periodic table and as isotope number 25

and it has isotope number 26. all of these isotopes exist in magnesium so magnesium exists in

uh in abundance on the earth and it has the isotope 24 25 and 26.

so magnesium is always going to have 12 protons that is what we are going to define as magnesium is that it's always

going to have 12 protons it doesn't matter what the isotope is so therefore if we have 12 protons we

can assume for now we have 12 electrons and that's because the number of protons and the number of electrons are the same

here we have our mass number of magnesium or three different mass numbers so for magnesium 24 our mass

number is 24. for magnesium 25 our mass number is 25 and for magnesium 26 our mass number is 26.

so now let's go ahead and look at our neutrons so uh 12 minus or 24 minus 12 is going

to give you 12 neutrons 25 minus 12 is going to give you 13 neutrons and 26 minus 12 is going to

give you 14 neutrons so in magnesium 24 the only difference for magnesium 24 is that you have 12

neutrons magnesium 25 you have 13 neutrons and magnesium 26 you have 14 neutrons

and again neutrons have no charge so you're changing the mass of the element

so your atomic mass unit for magnesium 24 is 23.99 for magnesium 25 it's 24.99

and for magnesium 26 it's 25.99 those are your amu's and again that allows us to use it so we do not have to

use those exponents but magnesium 24 25 and 26 do not exist in

equal percent abundances the most common is magnesium 24 so 78.10

of magnesium exists as magnesium 24. 10.13 is magnesium 25 and 11.17

is magnesium 26. so if we look at this percent abundance in a graphical representation you'll

find this in your textbook what we'll see is that magnesium 25

excuse me magnesium 24. so 20 uh

it has a mass number of 24 12 neutrons exists in 78.10 magnesium 25 exists in

10.13 and magnesium 26 exists at 11.17

so we can see that magnesium 24 has a much higher ratio if we're looking at our bar graph has a much higher ratio

magnesium 24 exists in 7.78.10 magnesium 25 and 10.13 and magnesium 26 in 11.7

these are not all equal if they were equal we would look at our bar graph excuse me let me go ahead and delete

this y-axis we don't need that if they were this is how magnesium actually exists if it was

all equal which magnesium does not exist like this isotopes do not exist like this

since there are three isotopes we would expect it to be 33 for each isotope so 24 25 and 26

and what we would see is again if they were all equal magnesium 24 would be in 33 percent

magnesium 25 would be in 33 and magnesium 26 would be also in 33 and

that would be if all isotopes were equal but we do not see that so that is this is a graphical representation of how

magnesium actually exists so when we're calculating the mass of an element

we have to take into account these varying percentages and that is what we're talking about

when we're talking about the atomic mass which we've learned about two slides ago the that atomic mass

is going to be how much an atom weighs and so we need to take into account each of

these isotopes each of these different percentages and so we can see that in our graphical

representation that each isotope is not equal so it's not just 33 you cannot take each of the masses and average them

out um and that is because they're not equal so what we need to do is we need to take

in that weighted percentage so we're going to go ahead and look at a different example

where we only have two isotopes because that's going to be a little bit easier so we're going to calculate our atomic

mass for chlorine and you will get to calculate the atomic mass for magnesium after we look at this

chlorine example so you have chlorine 35 and you have chlorine

37 chlorine 35 and chlorine 37. so your atomic mass unit of chlorine 35

is 34.97 and your atomic mass unit for chlorine 37 is

36.97 and you could see if we rounded this up this would be 35 and if we rounded 36.97

up that would be 37. so we don't use decimal places when we're talking about the specific isotope

so now we're going to talk about the percent abundance so 34.97 plus 36.97

again it's not necessarily going to be a 50 50 mixture but what we can assume is that we're we

need a hundred percent of these two atoms they both have to add up to 100 so chlorine exists in 75.76

and chlorine 37 exists in 24.24 so 75.76 divided by 100 is going to give

you your percent contribution to the mass so chlorine 35 is contributing at

75 or 76 which gives you a mass of 26.49 amuse

and fluorine 37 is contributing much less a quarter of all the chlorine atoms that exist have chlorine 37 and that is

contributing to an atomic mass of 8.962 atomic mass units when you add both of those up you will find that

chlorine has an atomic mass unit of 35.45 amuse

and this is the number you see on the periodic table that is where the molecular mass comes

from of chlorine is because you have chlorine 35 and chlorine number 37 again they're not

equal it's not a 50 50 mixture chlorine 35 you have in a percent abundance of 76 while chlorine 37 you

have a percent abundance of 25 so chlorine 35 is contributing to 26.49 atomic mass units

while chlorine 37 is contributing only 8.962 atomic mass units and so together those are going to equal the number that

you'll find on the periodic table the amount that chlorine actually weighs for this calculation this value your

percent abundance needs to be given if you don't know the percent abundance you would never be able to calculate the

contribution so your percent abundance needs to be given so let's look at this in a graphical diagram

so we're again we're looking at chlorine uh chlorine seven or chlorine which has a

atomic number of 17. on the periodic table you'll find that chlorine has an atomic mass unit of

35.45 and that's again because chlorine 35 we were just uh told that it contributes

75.76 percent and chlorine 37 is contributing 24.24

so out of that 35.45 75.76 of that is chlorine 35 and out of that

35.45 24. 24

is chlorine 37. again it's not a 50 50 mixture bromine has a 50 50 mixture of the two

isotopes chlorine does not so you do need to have that percent abundance given in order to calculate

uh in order to calculate the percent contribution towards the

molecular mass and you'll have lots of practice of this in the textbook for magnesium

and bromine and other elements that have two or more isotopes so again this is going to take practice

so let's go ahead and look at four point chapter four or section 4.6 which is electron uh energy levels

so 4.6 is electron energy levels it's a lot of slides to depict what's

going on here so here's the electromagnetic spectrum there's a wide variety of different

waves we have radio waves microwaves infrared rays waves all safe for

humans to be exposed to then we have the portion of the visible light spectrum

which is very small this is what we can actually see and then you'll have ultraviolet rays

which is anything higher than the visible spectrum are

actually quite dangerous to ourselves ultraviolet rays which is what the sun radiates um partially and then you'll

have medical x-rays and gamma rays and those are all you don't want to be exposed to those those are high energy

and uh anything below the visible light spectrum is considered low energy so that is the electromagnetic spectrum

so when we think about electrons we want to go ahead and think about electrons can or part of the particles can be

existing in different portions so now

up until this point we've talked about protons what's going on inside the nucleus so notice that section 4.6 is

all about electron energy levels so now we're focusing on what's going on outside the nucleus because we're

looking at the electron energy levels so now we're changing gears a little bit and this is again outside the nucleus

which we learned in the beginning of this lecture electrons are outside the nucleus so again up until this point

we've been focusing on what's going on inside the nucleus now we're thinking about what's going on outside the

nucleus so we're going to look at electron energy

levels and you can have this thing called the principal quantum number and that is

represented as n we are not learning how to calculate this quite yet but your principal quantum number one is

the lowest energy and seven is the highest energy and the way that we can think about

what's going on is inside the nucleus remember inside the nucleus are your protons

and your neutrons so what we're thinking about is we're

thinking about electron energy levels and this is outside the nucleus and these can move

they can move around and they can change energy levels protons and neutrons are not under most

normal circumstances not going to change so right now we're only looking at again we're only looking at electrons and

those because they're outside the nucleus they could move around and they can change energy levels so

um and we'll look at why that is in a little bit later so right now inside the nucleus nothing is happening inside that

nucleus outside the nucleus we can think about this lowest energy

level on this bookshelf is being closest to the nucleus it's the lowest in energy then um

the next energy level is slightly further away from the nucleus making it slightly higher in energy

and then the more uh the further away you get from the nucleus the higher in energy and

we'll talk about why that is in one second so the way that you can think about is

these electrons that are closest to the nucleus this orange book can jump into the next

available spot if there's a spot available for it just like this purple book

could jump to the next energy level up if there's space for it in the bookshelf so electrons can move around uh into

different energy levels outside the nucleus so let's go ahead and think about again let's go ahead and think

about what's going on inside the nucleus we're going to go ahead and look at lithium

so inside the nucleus you have three protons so we're looking at lithium outside the nucleus you have two energy

levels you have your first energy level and you have your second energy level at this point you do not need to know

how many energy levels that will be told to you at this point

you eventually will will be able to tell later on um when we get into electron orbital

filling which is the next section but right now we're just looking at lithium as two energy levels

again you're not expected to know that we have three protons inside the nucleus so therefore we know we're looking at

uh lithium with no charge again we are not looking at charged elements at all in this chapter we will get to that in

chapter six so right now you can assume that the number of protons has to equal the

number of electrons this is not always going to be true but the first two electrons are going to

be in the set the first energy level this lowest level closest to the nucleus

the second energy level out so this would be n is equal to two and this energy level that's closest to the

nucleus is n is equal to one that third electron is a little bit further away from the nucleus

and so what we want to think about is we have the first energy level

this electron is very close to the nucleus so what's going on is again you have this positive

and this negative charge are attracted to one another so that's going to be a lower in energy because the positive and

the negative are close to each other so those can balance each other out when you get a little bit further away

from the nucleus though so the second energy level that positive charge does it isn't as strongly attracted to that

negative charge so that's what makes it higher in energy and so it's a little bit confusing first

as a concept because we don't know that energy levels are not created equal and so we need to be told that so that's

what this pictorial diagram is explaining to us so you can have changes in the energy

level this electron that i have highlighted in this beige color can

go to this energy level with um with some help it doesn't just spontaneously do that but it could do

that with some actual help you can move electrons into

different energy levels and that is going to take energy so what happens is

and that's how light uh is is used whether it's visible light or not visible light so if you have your

lithium again i'm just using lithium in an example so you have your lithium the electron

and you promote that electron to an energy level further away from the nucleus then what

you're going to get is higher energy photons are going to be admitted and these are higher in energy

so when you're moving an electron from a lower energy level to a higher energy level you have high energy photons are

emitted and so these are higher in energy and this would be something like the x-rays or the gamma rays

on your electromagnetic spectrum uv rays something like that higher in energy when you have

an electron that is being it's still being promoted but it's being promoted to an energy level that's

closer to the original state you have lower energy photons are admitted and these are lower in energy

so in your let's go ahead and look again at our bookshelf when we have our bookshelf is being

promoted all the way let's say to energy level number five that probably wouldn't happen but if that did happen

then when the electrons come when the electrons are emitting their energy they're going to be much higher

in energy if you have this book right here this uh

beige book and you're only promoting it to the next energy level when that electron comes back down and is coming

back down into its normal state then you're gonna have a lower energy level um and that is

lower in energy something like radio waves and microwaves so again we're promoting an electron from one energy

level to another energy level and so if you're promoting an electron that's

from let's say n is equal to one to n is equal to two when that electron goes back down to the n is equal to one

energy state that's going to be lower in energy from our bookshelf diagram if you are

promoting an electron from let's say n is equal to one and you're promoting it to n is equal to five

when that electron goes back down to n is equal to one that's going to be something uh more

high in energy which is something like an x-ray or a gamma ray and that's what this pictorial diagram is explaining

so that's what's happening and how um electrons are

it's you know generating energy so inside an orbital you can have subshells

and again closer to the nucleus you have one type of subshell a little bit further away from the

nucleus you have two subshells three energy uh a principal quantum number so three energy states you have

three elect or three types of subshells and when you're four energy levels away from that nucleus you

have four types of subshells and we call these s

p d and f so those are the types of subshells that

you can have you could have an s subshell a p subshell a d sub shell or an f sub shell

and these subshells again are not all equal these sub shells are going to have

varying shapes so let's go ahead and look at just what an s sub shell will look like so it doesn't matter whether

your s is four three two or one all s subshells are going to have this shape so this is an s subshell

is always going to be this spherical shape that is an s subshell and again that can be n is equal to one n is equal

to two n is equal to three n is equal to 4 and so on and so forth it does not matter all s subshells have this

spherical shape if we go back to our subshell diagram we'll notice that p's what we have three

slots we have our first slot we have our second slot and our third slot and again it doesn't matter if your it's n is

equal to one and is equal to two uh n is equal to two three or four you have three slots all the time all highlighted

in green and those are these three slots so you have the first slot for green the

second slot in green and the third spot in that green diagram and this can be p is equal to two p is

equal excuse me for n is equal to two n is equal to three or n is equal to four it

does not matter all of your p sub shells look like this so you have your first box of green you have your second box of

green and you have your third box of green on the previous page so you have your first box your second box and your

third box of green one of those is representing this orbit this sub shell the second box is

representing this sub shell and the third box is representing this subshell and so that is again here's box one box

two and box three your d sub shells you have one two three four and five potential subshells

and again this only exists and n is equal to three and n is equal to four so if you go back to that book diagram

that's only n is equal to 3 and is equal to 4 and n is equal to 5. um so higher energy

orbitals uh only have this d option n is equal to 1 or n is equal to two do

not have d options so we would expect five different uh subshells so let's go ahead and look at

our d's and again we have that highlighted in our tan color so you have your d

your first one your second one your third box your fourth box and your fifth box so we

don't want to write out these pictures every time you can see they're quite complex to write out

so we just write them out as these boxes one two three four and five boxes but one box represents

let's just say we're gonna call this box one two three four and five those five boxes are one two

three four and five those are all the different d's

and then last but not least we have f's represented here in this purple so i'm going to

show a this purple subshell is one two three four five six

and seven lots of uh subshells and this only exists when n is equal to four

or higher so we have one two three four five six and seven

and again that is represented as that first box our second box our third box on the previous diagram our fourth box

our fifth box our sixth box and our seventh box so why am i showing you this slide these are the varying shapes

of what those boxes are representing you do not need to know this okay you do not need to memorize this i

don't want you to memorize all of these different shapes what i do want you to memorize

or what i do want you to know is that again you do not need to memorize all these different shapes

the point of this slide is to actually show what these boxes are representing they're not just arbitrarily given boxes

they actually have different shapes so you do not need to memorize all of these different shapes

but what you do need to know is that s subshells p subshells d subshells and f subshells

all have these different subshells you don't need to know what those subshells actually

look like but you do need to know that those sub shells exist so now let's talk about what that

actually means with all of these subshells so those are the shapes and this is how orbitals fill so this is

4.7 which is all about electron configuration and this is going to take practice

you have your electron configuration and again this is from we can think about

this being from the previous slide of the shapes so remember all s subshells it doesn't

matter what the n is what the number is so one two three four five six seven all of those have this spherical shape

the size of that shape can vary again we're not talking about that we're not talking about the sizes of these but all

s subshells have this spherical shape and in that spherical shape you can have two electrons can fit in there and so

you'll have this is one electron and you'll have your second electron

represented as this half arrow is represents one electron and we can see that they're opposite of

one another um this first electron is where you have half of the arrow pointing up and your second electron is

where you have the other half pointing down but each represent one electron and you don't need to know what that

represents but you do want to show that one is up and one half arrow is down that's what this symbol is showing

so each of these boxes can hold two electrons so a grand total of two electrons

so each box holds two electrons max

okay so each box will have two elec whole be able to hold two electrons maximum this

is one representation of electron configuration or how orbitals fill how some shells

fill to me this is kind of complicated i like it's the exact same diagram or it

looks a little bit different but it's telling us the exact same thing i like this one a lot better

so again you still have your n is equal to 1 2 3 4 5 6 7 8 so on and so forth but on this diagram it's much easier

because you will be able to follow what is uh going on and i'm going to choose a gray highlighter you'll be able to

follow what is going on with regards to the arrows so all you have to do is you're gonna

and we haven't seen an example yet but we're just learning how to read this table

where we learn how to read this diagram so we're gonna when we do start filling we're gonna fill our one

subshell burst and then you'll follow the arrow and then you fill your 2s subshell you follow this arrow you you

fill your 2p subshell and so on and so forth so you're going to follow the arrow all the way along when we start

filling electrons the same thing is true here you're going to fill in your 1s first

and then your 2s and then that goes to filling in your 2p and then your 3s so it doesn't matter which diagram you like

to use for filling electrons your electron configuration you can use this diagram

or you can use the one that i have in this handout which is this diagram it doesn't matter whichever one you want