Comprehensive Chemistry Review: Isotopes, Ionic Compounds, and Molar Mass

hello AP cam Squad here we are with our chapter 2 lesson uh make sure you guys have a notebook ready and a quiet place

to uh listen to the videos again it is a review from what uh you already have done in your chem one classes

so let's get ready and so if you look at the periodic table the number on the top is representing the

atomic number that is the number of protons in a neutral atom and the number that is at the bottom is representing

the weighted average which is based on the atomic mass which is based on the Isotopes so let's look at that

so now what is an isotope isotope is the basic definition is atom of the same element but different mass number that

means the number of protons are the same but the number of electrons are different so if you look at this example

Boron 10 we can say that it is 5 protons by looking at the periodic table based on the mass number we can say it is 5

neutrons if the mass number is 11 that means the number of neutrons are different the proton is something that

is specific to an element most of the elements have at least two or three Isotopes however aluminum fluorine and

phosphorus are the only elements that have one isotope here are isotopes of hydrogen so if

you're looking at this example over here as you can see that the number of protons are the same but it is the

number of neutrons that are different and these are the different isotopes now if water is uh having the different

isotope the mass and the density is going to be different so that is something that you should be able to

remember and understand now how do we Mass spectrometer is an instrument that is used to help us

figure out the abundance of each of those Isotopes and based on their masses you will end up getting a different

projection on a screen and you get a graph that tells you the abundance of each isotope with a certain Mass so you

don't have to know how a mass spectrometer works but we will work on how you should be able to read a graph

that is generated by a mass spectrometer so here is the actual masses of the atoms are always less than the sum of

the masses of the subatomic particles because of the mass effect if you know the masses and you know the

abundance you can calculate the atomic mass here is the formula that you all should know so if you want to write it

down I would recommend writing it down atomic mass is percent abundance you have to train the person to a number by

dividing it by 100 multiply by the mass of the first isotope at the percent abundance and my mass of the second

isotope depending upon how many are there you will keep doing it this is what is called the weighted average of

the Isotopes this is basic important fundamental formula that you should be able to use

so let's look at this example Boron is 19.9 percent Boron 10 80.9 percent is border on 11 so you can use the formula

over here and you are able to figure out so instead of you you are going to use the

formula as a m u so here's the problem try to pause the video and see if you can solve it

take a minute read so if you look at this problem first you are going to uh in this case because

I've only given the two isotopes you could just add the mass divided by two you get the average

the numerical values therefore you could say that the percent abundance of each of this isotope is 50

because they were just two of them that were given to you and the masses were very equal

now elements molecules ions and compounds so we should be able to understand a difference between an

element this is an ionic compound which is between a metal and a non-metal this is a molecular compound because it is

all nonmetals and this is an element by itself the other type of elements that you

should know are the diatomic elements there are seven diatomic elements and if you look over here this is hydrogen two

and this kind of makes a 7 on the periodic table so you should always remember that you're going to write them

in this way the other thing you should be able to identify on the periodic table is the

elements um where which are your Metals so everything that is blue over here are

all your Metals everything that is orange over here are your non-metals hydrogen is a non-metal and everything

that is green here are your metalloids so make sure you're able to identify you should be able to identify the charges

of them and that metals lose electrons to form a cation and non-metals gain electrons to form an anion so these are

your anions you should be able to identify the charges of all of them so this one are plus one plus two plus

three this can be plus or minus four minus 3 minus two minus 1 and noble gases are zero now when you look at the

transition elements over here these transition elements can have multiple charges so we're going to talk a little

bit about it so as I showed you in the slide when you look at a metal metal is going to lose

the periodic table sorry if you look at the metal it will lose an electron and sodium loses one electron as a result it

has a plus one magnesium has to lose two electrons aluminum has to lose three electrons and just we'll talk in our

next unit but the elements lose electrons to have an octet of electrons to get stability

now if you have a transition metal you use a Roman number over here to show the charge on them so the Roman number is

representing the child charge on the transition metal so as I showed you these are a few of

the elements here are the charges uh when you're naming the compounds you have to remember the name of the metal

Remains the Same but the name of the non-metal ends with an IDE so here are some examples once again

pause the video see if you guys can figure out the common charges by just looking at the periodic table I have

showed you how we can actually it comes from an electron configuration in case you do not remember how to do all this

electron configuration we are going to talk about that in chapter in unit 3. but at this point if you're able to look

at the periodic table and identify the charges it is good enough so one thing that I would like to reinforce here

remember zinc always has a charge of plus two silver always has a charge of plus one so those are the two transition

metals that you will not use a Roman number because they do not have multiple charges

now if you look at nickel how would you figure out the chart because it's a transition element you basically look at

the highest energy level which is 4s2 so you are going to remove the electrons from the highest energy level and as a

result the charge on nickel is plus two and if you look at gallium now if you look at gallium it is plus three because

we have 4s2 and 4p1 they both are in the fourth energy level so we'll be able to remove the electrons from both of them

so this is how you would do it for the transition elements if you look at zinc this is for S2 so you always remove the

electrons from the highest energy level and that is the charge on those elements you have to memorize all the polyatomic

ions it is not something they're going to ask you but it is expected that you know

them or hopefully most of you have memorized it in your cam one classes here is the list in case you do not have

it I would recommend uh taking a screenshot of it and saving it here ammonium is the only polyatomic ion

that has a positive charge all the other polyatomic ions have a negative charge these are the most common ones that some

of us forget is so the way you would remember is hypo is the lowest number so the least number of oxygen hypochlorite

just chloride you add one more oxygen the charge is the same on all of them chlorate eight always has one oxygen

more than the eye time like sulfate sulfate is so4 2 minus and sulfite is so32 minus so ite has one less oxygen

than 80. so this should help you with that and perchlorate is clo4 now instead of

perchlorate if I made it per bromate everything Remains the Same the only thing that changes is BR instead of

chlorine so make sure you these are the common ones that you would see make sure you know these polyatomic ions

here are some more examples see if you guys can figure out the charges of all of them

and if we look again I'm just showing you the electron configurations which I just went over on the previous slide

see if you knew those for chlorate ion and try to practice I'm not going over all this you can look at

those and I'm sure you should be able to remember this from your camera classes foreign

if you need to take time to see how the charges are once again if you do not know how to write the electronic

electron configuration at this point or you have forgotten from your chem1 classes we are going to go over it later

on now how to write a ionic compound and how to write the name of a compound and

how to come up with a formula this is something that is expected in class you we cannot afford to do make mistakes in

writing the correct formula so as we are looking over here calcium carbonate that's a name here is a

Formula it is formed with two ions calcium two plus we just went over how you can figure out the charges of an

element on the periodic table and know the uh polyatomic ions now the rule of

writing an ionic compound is that it is between a cation and the ation the ionic compounds are stable because the metal

wants to lose electron and the non-metal wants to gain electrons so there's a complete transfer of electrons so if you

look at this example magnesium wants to lose two electrons fluorine wants to gain one electron so therefore we have

to have two fluorines in order for magnesium to be able to give two of them therefore the correct formula of this is

MGF MGF 2 because you're using two of the Florence I hope you all know how to

write the uh formulas correctly now look at this example over here try to identify which are the correct

formulas and which are wrong uh take a minute and pause it and see what you come up with and then look over the

slides to see the answers so if you look over here the first one was incorrect just I'll go over one of

the example here because as you looked at the periodic table and saw that aluminum has a charge of plus three

chlorine has a charge of minus one as a result we are going to need three chlorine and the correct formula is

going to be aluminum chloride and this one is also wrong because of the charges as you can see on the

periodic table right I hope you all did great with this question

now here I have given you the name the formulas go ahead and try to see if you can name them try to make sure you have

already memorized your polyatomic ions at this point when you're working on it and if you're not able to recall some go

back and look at them and make an effort to memorize those so I hope you did that right potassium

actually sorry it should be potassium sulfide not potassium iodide sorry for that mistake here

now one thing over here to remember is Cobalt sulfate because it is a transition metal you cannot just write

Cobalt sulfate as the name you have to specify a Roman number when it is a transition metal

I hope you all did that ammonium phosphate and clo2 is chlorate therefore calcium hypochlorite

all right I hope you all are doing great with this now here I have given you the names of

the compound pause it and see if you can write down the formulas of them so first thing is when the name is given

you identify the charges now you balance the charges since this is plus one and this is minus two so you would need two

of ammonium therefore when it's a polyatomic ion you put a parenthesis around it and that is going to be

ammonium carbonate foreign the name does not change while if it is

a binary compound we have to remember that the non-metal ends with an IDE therefore calcium iodide

now when we look at this the Roman number is plus two again it's a binary compound it's not important that you

know if it is a binary compound or not but that says calcium bromide aluminum

phosphate and silver acetate now over here again this is not right as I'm seeing this you

do not put a Roman number for Silver acetate because silver always has a charge of plus one so you do not have to

use a Roman number for Silver and for zinc now here are some more compounds let's

see if you can name them now the point over here is you cannot just name NF as

nitrogen fluoride because it is basically a molecular compound so if you made a mistake over here and you were

not able to differentiate we'll just go over the slide for the rules when it is starting with an H you have to remember

that it is an acid um the name of the acid is hydroiodic acid if you do not remember how to name

the acid first week of school we will go over naming Assets in class so don't worry about it if at this point uh you

are struggling a little bit with that but naming ionic compounds and molecular compounds are important

here again this is a molecular compound so it is going to be phosphorus Penta iodide

so I hope you all were able to differentiate those things I will have a slide in a minute about uh

the molecular compounds now here this is the only concept that you have not learned in your chem 1 classes which is

Coulomb's law basically what Coulomb's law is saying as the iron charges increases that traction increases so if

there is a going to be a compound any Plus versus CL minus compared to mg plus two and oxygen minus two there is going

to be more attraction between magnesium and oxygen there because of the coulomb slot is going to be more attracted to

each other while n a plus and cl minus are going to be less attractive which is going to affect their bond length so you

should be able to look at them and see which one have more attractive phosphates more attracted they are more

ionic characteristic they have more lattice energy would be needed again we are going to talk about it later on as

the distance between the ion increases the attractive forces decreases so over here this will decrease

and as the charges increase attractive forces increase so this is all you need to know you're not going to be expected

to solve using this formula so you can see that this is an inverse relationship between distance and the force and the

charges and the forces are direct relationship okay once again do not worry about any

problem solving for this uh you will be doing so this is what electrostatic attractions are forces when you look at

an ionic compound they are in a lattice structure arranged and they are attracted by electrostatic forces you

will be doing a simulation uh after you've finished watching this video which will help you understand a little

bit more about the Coulomb's law and how the attractive forces work so make sure you do that after that you will start

working on the assignment on this chapter once again this is just another slide

over here trying to show you over here so if you're looking at these charges the bond length is going to be smaller

and while if the charges are higher the bond length the attractive forces are more and the distance is going to be

larger once again try to understand the basic we'll go over this in class little bit more in detail since it's a New

Concept so do your best and the simulation should really help you guys

so the importance why we are talking about this because it helps us predict the melting point so if you look at NaCl

has a melting point of 100 and 804 while the melting point of Naf is 993 so can anybody take a minute and

think why that is and so basically over here if you're looking at it the charges are same for

or both of them they are plus one and minus one but now the distance for fluorine fluorine is much smaller than

that chlorine so since it is smaller the attractive forces are stronger and as a result the melting point of any f is

much higher than that of NaCl so the larger distance makes NaCl have a lower melting point I hope you were able to

make that connection so that is an application that you should be able to understand at this point

now if you look at this another example look at the same idea any plus and oxygen is minus two but if you look over

here calcium and oxygen they both have plus two and minus two so higher charges and as you can see that the melting

point is much higher of calcium oxide than that of sodium oxide so this example is trying to show you the effect

of the charge higher the charge higher the melting point now Coulomb's law is something that we

are going to keep talking in many several units and we will be talking more about it right now we have just

focused on this part you do not worry about this but understanding this effect and being able to apply it when a

problem is given we are going to talk about the periodic trends and talk in more details the next slide is also

showing you what are all the places that we are going to use this so you can just read

as of now here is an example so you should be able to understand in terms of ionic bonding at this point we will talk

more about covalent bonding periodic trends uh imf's solution unit and we'll talk about the polyprotic acid so

Coulomb's law is a very essential law that we are going to use to help us understand many other Concepts in

chemistry all right so the next unit is mole I'm sure you all remember more from your

classes and have done a lot of Dimension analysis um

so we'll be using it is a quantitative way of measuring in chemistry uh one mole uh is the amount of substance that

contains as many particles so it is 12 grams of carbon contains how many molecules that is where we got the

number 6.02 times 10 raised to 23. so when come small comes the molar mass I hope you all remember how to find the

molar mass of each compound so if aspirin is given to you carb c9h804 you multiply 9 by the mass of the

average atomic mass which is on the periodic table the bottom number hydrogen a times the molar mass of

hydrogen oxygen you add them all together and the unit is grams per mole if you're looking at a hydrate this is a

hydrate copper Roman number two chloride dihydrate in the molar mass you add the mass of the water

here is a molar mass of the other compounds so you should be able to figure out the molar mass of the

compound once again I hope you all remember this from your chem1 classes now once you have calculated the mass if

certain mass is given you should be able to convert it into moles using Dimension analysis you have to show all the work

so if this is the grams of carbon I have you get this number from the periodic table these many grams is one mole and

as a result you know how many moles it is and again at this point you will have to remember sickness significant figures

they're important though it is just one point I will be emphasizing that one point on every assessment on one of the

problem so let's try to do this problem pause the video for a minute and see if you

guys can do it here I've given you the moons of propanol actually this problem is already solved here you will

calculate the molar mass of the propanol if it's a compound you cannot just directly get it you have to do extra

steps to help you get the molar mass so here I've showed you how you do that

three from carbon seven is coming from hydrogen now be careful there is one more here so therefore I have eight here

and we have one oxygen and these numbers here we guard them from the periodic table you add them all together and you

end up getting the molar mass and then you can convert the moles into how many grams it is

now person composition is another concept that probably you all remember it is basically if a compound is given

you take that atoms of each element multiplied by its atomic weight and divide by the total mass of the compound

that is a molar mass times 100 will give you the percent composition here is an example for the compound that

is given to you most of you did a great job with this in your chem 1 classes I'm not that worried uh so I hope you all

these numbers are making sense how to do it but make sure you are able to do this problems and you will get practice once

you will work on your chapter to assignment these are very simple steps but they are

very important they are uh one or two steps of the bigger problems that you will be doing uh as we move along

right so I hope this makes sense so here's another example what is the person composition of calcium hydroxide

figure that out not reading over I'm sure most of you all this is making sense it's just a

quick review of what you already have done enough in your classes now the next concept was empirical

formula a pure compound always consists of same elements combined in the same proportion and therefore we can take

their person weight now if you look at uh if you know the percent of each of those compound we can figure out the

empirical formula in certain cases empirical formula and the molecular formulas are same sometimes they are not

empirical formula only show the simplest ratio ionic compounds represent their simplest so ionic compounds are

empirical formulas molecular formulas show the actual composition of the compound so let's see how we are going

to convert an empirical formula to a molecular formula so here is the steps if you are given

the percent first thing is you convert the percent into grams so we assume we have 100 grams of substance then you

convert the grams into moles because when you are looking at why you're converting into more what

this is telling you that if I have this one mole of water it needs two moles of hydrogen and one mole of oxygen so this

is the lowest mole ratio of the elements to form this compound so you convert that grams into moles now whichever

element has a lower moles you that becomes a number one and you divide everything else by that lowest mode so

you get the ratio and here you end up getting the empirical formula of the compound

but so here is an example you are given the percent of the

elements since you were given the person you converted into grams then you convert the grams into moles

now once you have the moles of both of them since we have lower moles of boron you multiply both have divide by 7.5

moles now if you do not get the whole number you have to multiply this by two now you

are not just going to multiply one of them by two this is a very common mistake that the many students do is you

also have to multiply Boron though you've got one over here you have to multiply that also by two therefore the

empirical formula of this compound is b2h5 great so these are basic problems you

would be seeing on your first unit one test now how are you want to convert an

empirical formula to a molecular formula so once you know the empirical Mass and you know the molecular to figure out

the molecular formula if the molecular mass is given to you basically what you have to figure out the N value to figure

out your n value the formula is molecular molecular mass

divided by the empirical Mass and most of the time you will get a round number so let's say if you get

1.98 you are going to assume that the N value is 2. if you get 3.99 you're going to make it 4. that is your end so

whatever let's say we got a empirical formula as c2h5o2 now your n value and you were

given the molecular formula and you get the number two you multiply the entire empirical formula by 2 and as

a result the molecular formula this compound will be C4 h10o4 okay next time I'll make sure I use a

better color I'm sorry for the bad color Choice here so here is the formula that is given to

you so molar molecular formula divided by the empirical formula amplical mass will give you the N value

I just showed you in the previous slide so here uh just uh extension of the first problem we

already figured out the empirical formula of the compound now what will be the molecular formula they have given

you the molar mass of the compound so you know the molar mass from our empirical formula that we had calculated

in our previous slide you will have the empirical Mass you divide it you get two units and as a result this is your

molecular formula of this component I hope this is making sense and you are happy to recall most of the stuff and

feeling proud of yourself if you're able to recall all this give a pet back give a pet to yourself

now we are going to be doing this is going to be our first lab that we'll be doing within the first week is where

we'll be given in hydrate so you should know how to name and hydrate you name the ionic compound the way you name an

ionic compound whatever the end value is so let's say if it is one you say monohydrate five you will

say pentahydrate hexahydrate that is how you would name them right so here is a slide showing you how

you name and hydrate now what will we are going to do a lab where we are going to take and hydrate

so just imagine if we're going to take and hydrate and you're going to heat it up you're going to get rid of the water

so uh ionic compound that does not have water is called a anhydrous salt so if you have the mass of anhydrous salt and

you have the hydrate you can figure out the mass of the water that is lost and then

you can do the mole ratio for them knowing the mass and the identity of this once you know it you can figure out

the N value which is moles of water from the hydrate and the moles of the anhydrous salt so if you know the grams

you can convert it and as a result you can figure out if your hydrate is a dihydrate pentahydrate or a heptahydrate

so you'll be doing this lab where you'll be given an unknown hydrate and you will have to figure out what type of hydrate

it is you're going to get a copper salt and just to show you that mass spectroscopy is further used so when you

figure out a molecular formula mass spectroscopy can be used to help us figure out the functional groups on a

compound which again organic chemistry is not on our AP course so you do not have to worry about but that there's

another application of a mass spectrophenometer all right so that is it from me on

chapter