How to Write Electron Configurations for Ions: Transition Metal Tips

hello everyone and welcome back my name is mr cobalt and in this video i'm going to go over how to write electron

configurations for ions and show where those electrons are coming from so that way we don't make a mistake with regard

to like making sure right and writing the right electronic configuration to show where those electrons are coming

from all right so here i have my orbital diagram i'm going to be filling in this orbital diagram uh using the

different principles and rules so for example i'm going to be using aufbau principle right so to build up from low

energy to high energy i'm going to be using the polyexclusion principle so that way um to show that

two electrons maximum can go into each orbital each line is an orbital and those uh those electrons should be

uh opposite spin so spin up and spin down in each orbital um also i'll be using hund's rule right remember hund's

rule says that if you have any orbitals of equal energy when you're adding electrons to each of those orbitals you

add them one at a time and they have to have the same spin so maybe spin up spin up spin up before you start pairing them

up okay so let's get into this so um here we have uh some atoms i'm going to

write out the electron configurations for the um the neutral atoms right and then we're

going to see where those electrons come from and what that electron configuration for the ion would look

like okay so let's start with magnesium magnesium is number 12 on the periodic

table so we need to put 12 electrons in there because we're assuming neutrality right now

so let's get into this so 12 electrons so i'm going to put starting from low energy

spin up spin down to in in in the 1s and then

the 2s gets spin up spin down so that's 4 and i'm going to add one at a time spin up

spin up spin up and so there's three and then i can

start pairing them up spin down spin down spin down okay so that so far that's

10 and i need two more so i'm going to put spin up and spin down so that's 12. so

now i have my 12 electrons and so here um

we got to figure out where the electrons are going to be coming from so if you know the periodic table if you

know where this element lies you can figure out the charge from there remember the octet rule um

all atoms want to be like noble gases so they're going to lose or gain electrons based upon uh which is easier to do so

they want to get that full outer shell that valence shell they want that to be full and they're going to lose or gain

electrons to get that full shell and so here you can see that the last electrons the highest energy

level is three and so here to get that full shell with your s and

your p you need either six more electrons so magnesium can either add six electrons

to that full shell or it could lose these two electrons and then next shell would then be the full shell so 2s 2p

together would be your full 8 and so it's a lot easier to remove two electrons than it is to gain

gain 6. so magnesium will lose those two electrons so lose these two electrons here

from from the 3s which is the at this point the highest energy level is three and

you can tell it's the highest because you got the three there so that's where the electrons are going

to be pulled from so they're always going to be pulled from the highest energy according to

the shell number here the energy level number here all right so you lose those two

electrons there right so then

if we write out the uh the electron configuration for magnesium before we move those electrons would be

1 s 2 2 s 2 2 p 6

3 s 2. so we lost the 3 s electron so this would be the electron configuration for

the neutral atom but we lost those two electrons so we would remove the 3s2 and so that

would be the electron configuration for the ion magnesium with a two plus charge

okay let's try the next one so we have phosphorus phosphorus is number 18 i'm sorry number 15 on the periodic table so

we're going from let us add our electrons back oops

so we have spin up spin down so here we have 12 electrons we need three more electrons to get 15.

so we're going to add one two

three notice i'm i'm following hund's rule so those three go are going to go one at a time singly into

the three equal orbitals and that's it so we have 12 13 14 15. so now

we can figure out what phosphorus is going to do so we have it could either gain three

more electrons or it can get to get that full outer cell right that third full outer cell with the s and the p

or it could uh lose these three electrons lose those two

electrons so lose five electrons to then have a full outer shell it's going to be a lot harder to remove for five

electrons than it is to gain three so it will gain three electrons from some other atom or atoms

and so spin down spin down spin down so if we write the

electron configuration for the atom before it gained electrons it would be

1 s2 2s2 2p6

3s2 and it would be three p three

right so before we added those three electrons it was three p three but when it gains those three electrons it will

be three p six so you add a 6 there and so that would be the electron configuration for

phosphorus with a 3 minus charge okay

let's move to the next one so calcium calcium is number 20 on the periodic table so here we have

uh right now what is this we have 20 plus

6 i think that's 26 let's count so we have 2 4

and this is 6 here that's 10 sorry that's 18. so we have 18 here so 18

uh calcium is number 20 so we need two more electrons

so we add two more electrons here and so now we write the lewis dot structure i'm not

i'm sorry i keep mixing up lewis dot structure we're gonna uh write the electron configuration for uh calcium

before we take away any electrons or gain any electrons so the electron configuration is 1 s

2 2 s 2 2 p 6

s two three p six and four s two okay so

that is the electron configuration for calcium as a neutral atom again we come here

notice that the highest electron our electrons are in the 4s 4 is the highest number we have

those electrons are going to removed first so you so far the pattern is that the electrons are being removed from

the highest energy level so 4s here they were removed they were added to the highest to make that full shell

here they were subtracted from the 3s right to re uh so that 3s was the

highest one so here uh the 4s is the highest so those electrons are going to be the ones

to remove be removed again you could add six electrons but that

would be hard to do it'd be easier to lose those two so calcium tends to lose two electrons as you know it's in group

two so if you know the relationship of charge and the periodic table group two elements tend to have a two plus charge

and that's why so these electrons would be removed and so since these electrons would be

removed then we would erase the 4s2 here and that would be the electron

configuration for calcium two plus so that would be the two plus charge there

so so for the positive ions we we are removing the electrons

first from the outer uh the most um how should i say the uh highest energy shell

okay let's try chromium let's do chromium this is where it kind of gets interesting

so chromium is number 24. so we got to put those electrons back so that's 20 and

now the next highest energy level is going to be the d and so we have four electrons put in so we're going to put

them in following hundrel so spin up spin up spin up i skipped one

spin up so our four electrons are all same spin they're one in each orbital

so this would be the orbital diagram for chromium so let's write out the

the electron configuration so here would be 1 s

2 2 s 2 2 p 6 3s2 3p6 4s2

and 3d4 okay so this is the electron configuration for the neutral atom of

chromium okay so what would be the ion um where are these electrons going to come from

remember what i said the electrons are going to come from the uh the highest energy shell

and that is the number that is determined by the number in front of the letter right so you'll notice here

that the 4s these electrons here are in energy shell number four even though here according to the orbital diagram

these are higher energy level so here even though this is a 3d it looks higher

the electrons are being taken from the 4s this is the higher number so the electrons are taken

from this here okay so we remove those electrons not these so

we these are always removed first so let's assume let's uh chromium is a transition element it can have

various charges let's assume that it has a plus one uh let's say it has a plus three charge okay so if we give this a

three plus charge we're going to need to remove three electrons the first two electrons are

removed from here not here so we don't remove three electrons from

here first right that would be the wrong way to go about it the electrons would be first removed

from the 4s because that's a higher number and then you would remove from the 3d

so these would be removed so remove those that's two and then for the three plus we need one

more electron so we would remove one of the electrons here and so now the electron configuration

would be 1s 1s2 2s2 2p6 3s2 3p6 3d3 so then we would get rid of

the 4s2 and replace that with 3d3

so that is the electron configuration for the chromium 3 plus ion this is typically what happens when we're

dealing with the transition elements so you got to be careful when you're figuring out what the electron

configuration for ions that are are the transition elements all right so what about uh

iron iron again is a transition element it is number 26 so let's put in

26 so we have 20 1 2 3 4

5 6 and again the uh

for the neutral atom the electron configuration would be 1 s 2 2 s 2

2 p 6 3 s 2 3 p 6

3 oops 4 s 2

3 d and that would be uh six three d

six but once again just like before um

we have our two electrons here in the 4s but we have electrons in the 3d when we're trying to figure out the charge or

the electron configuration for our iron we remove electrons from the 4s before the 3d because 4 is higher than 3. so

this is the higher energy shell so remove electrons here first before we start removing electrons there

so again iron can be a plus it could be a plus charge be a plus two it could be a plus three

so if uh if iron is a plus three charge right once again

right if it's a plus two charge then we would just remove those two electrons and then the electron configuration

would be 1s2 2s2 2p6 3s2 3p6 and then 3d6 if it's a 3 then we remove these plus 1

over there so if we move those electrons and remove one here right

so now the electron configuration is going to be if we remove the 4s to here and we replace the 3d

3d6 with 3d5 and oops color

so that's going to be 3 d 5

then that would be the electron configuration for for iron

and then finally for bromine like so bromine is

number 35 so here we add

our two electrons 20 25 26 27 28 29 30

and then we start adding here 31 32 so the 3d then the 4p and so now

we have bromine bromine as one two three oh wait hold on a second

uh 35 so we have one two three four uh 10

18 20 that's going to be uh

20 30 and then 32

okay so here um bromine i looked uh 35

oh 35 i forgot electrons 30 i said 32 but this is 35 so we have 33 34

and 35 that's much better that's less confusing okay so now here

you can see that the energy level the highest energy level here is four and it's almost full it's got seven

valence electrons in there and so now bromine can either add one or it can

lose seven it's a lot easier to lose to gain one electron so it's going to gain that one electron

like that and so the electron configuration would be

1s2 2s2 2p6 3s2 3p6 4s2 3d10 and then 4p6 so let's write that so it's going to be

1 s2 2s2 2p6

3s2 p six uh

four s two three d ten and then four s uh no i'm sorry four p

six and so that would be the electron configuration of bromine with a minus

one charge and you can see that they have a full outer shell there so that's it for this

video i hope that is helpful for uh writing the electron configuration for ions you got to be really careful

about the transition elements remember that you're going to remove electrons first from the highest energy level so

especially for the transition elements that's going to be probably the s orbital so you

so you're going to remove electrons first from those and then if you need to still remove electrons then you start

removing from the d uh d orbital or d sub sub level uh i hope this was enjoyable i hope you

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