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Chapter 4.1b Charges of ions

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welcome to the second video for

chapter four section one on ionic

bonding in this video we'll be

predicting the charge of common metallic

and nonmetallic elements and writing

their electron configurations

uh we're going to talk about the

electric electronic structure of cations

first and then we'll

talk about anions later so uh just as a reminder

reminder

uh when you are generating an electron

configuration we use the aufbau

principle to build up from the bottom

we put electrons into the most stable

orbitals first and the least

stable orbitals last um and when we lose

electrons when when these elements lose

electrons to become

uh ions cations they go they do the

reverse right they lose the least stable

electrons the highest in energy

first and then they lose more stable

electrons later

also full shells tend to be more stable

elements will lose enough lose enough

electrons to

sort of mimic the noble gas

configurations where where the where the

valence shell is completely full

uh so we'll talk about these in groups

because it makes a lot of sense to talk

about these as as

sort of periodic trends right um their

sort of properties uh we'll start out

with groups one and two so these are gonna

gonna

contain you know your common elements

sodium magnesium calcium potassium

um if you are interested in biology you

will recognize all of these guys

um and a bunch of these other ones as

well so this is this is group one and

group two

these as you might expect tend to lose

their outermost valence shell and they

lose their s

electrons so if you look at sodium for example

example

um sodium the electron configuration for sodium

sodium

is 1s2 2s2

2p6 and then 3s1

so we're looking at sodium it's last

electron its valence electron is in the

3s and there's only one of them

uh we can also write this if we want to as

neon plus 3s1

when sodium uh forms an ion it tends to

form a

one plus cation because it loses this 3s

electron and it becomes uh

it just has the configuration of neon

uh group two elements so for example

calcium and i'll scroll up just a little

bit so you can see this little better so

if we're looking at calcium we can think

about calcium

uh and i'm just gonna write the

abbreviated form of calcium's electron

configuration so it is argon

and then its valence shell is 4s2

so this element tends to lose both of its

its

s electrons and it forms a two plus ion

which has the electron configuration

that is just the same as arkon

so groups one and two tend to lose their

complete valence shell which is their s

orbital and uh so group one tends to become

become

a plus one and group two tends to become

we'll think about a different set of

metals next so we'll think about

uh the metals that are in groups 13

through 17 and

that's these guys um i've drawn a really

awkward triangle around here

we're going to ignore for now the

metalloids they do some weird things uh

we're going to focus on

the metals over here in the p block so

they also

tend to lose their uh valence shell right

right

they tend to lose their valence shell

but for these there's

not only s electrons but now there's p

electrons as well

so if we take aluminum as an exception

we can write its electron configuration

as neon and then 3s2

3p1 so you would predict

that aluminum would lose all of its

valence electrons it would lose all of

its um

its third valence

electrons and that is in fact the case

aluminum becomes a three plus ion and it

has the same electron configuration

as neon there are some exceptions near

the bottom of the table

so these guys down here in the p block

but down near the bottom of the table

um have a weird thing that happens where

you can you can predict that thallium is

going to make a three plus just like

aluminum it will lose

um all of its valence electrons lead

it's going to make a four plus tin same

thing's gonna make a four plus bismuth

is going to make a five plus

uh cation but they actually also have

something else that happens

where they keep their valence s

electrons and this is called the inert

and essentially what happens is the uh

the s electrons have a relatively low energy

energy

and um they just keep them so in

addition to making the sort of

predicted three plus four plus and five

plus ions they actually make

so tantalum for or sorry thallium makes a

three plus but it also makes a one plus

uh and tin and lead tend to make

uh four plus the expected four plus but

they also make two pluses

and then bismuth um tends to make

the expected five plus ion but it also

makes uh

wow uh bismuth will also make a

a less expected three plus ion due to

this inner pair effect where it keeps

its valence

one additional uh exception is mercury

mercury is actually a transition metal

here but um

it can form both uh mercury two plus and

it can actually form this

uh diatomic ion where there's actually a

bond between the two mercury

ion atoms and then it makes uh

next we'll talk about transition metals

uh transition metals are a little bit

weird they do a lot of things one of the

things that's really key to remember

with transition

metals is when you're using the aufbau

principle to fill

your valence electrons when you're

building an electron configuration

you fill the four s's and then you build

and then you fill the three d's

but it turns out that the four s's

actually empty first

so the valence s electrons are actually

less stable than the d electrons when

you are

losing electrons to form cations and so

you tend to lose those before you

lose the d electrons uh also there are multiple

multiple

options uh for for your transition metals

metals

and uh that that is just an unfortunate

effect of there's

um yeah the the dd shell is

uh complicated um one of the

the really common ones is iron so iron has

has

an electron configuration if we write it

out it is

argon with 3d6

and 4s2 so

if you look at this you might say well i

think that it would probably lose its 4s

electrons and yes in fact it does it

will form

an iron two plus ion which is uh

has the electron configuration of just

argon with the

3d6 electrons but it actually will also

lose one electron from the

the d shell sometimes and you can

actually also get

an iron three plus and that essentially

is just

uh it has the electron configuration of argon

argon

with uh d five um

and this actually points out that we

talked about full shells

have uh are extra stable there's they're

a little bit more stable but actually

half shells um the half uh so if you

have five electrons

in five out of 10 electrons in your d or

three out of six electrons in your p

orbital um there's actually that last

electron is slightly more stable

um and so that's why iron tends to make a

a three plus as well so

in general we're not going to ask you to

memorize um

transition metals because they do form multiple

multiple

uh multiple cations there are a few that

you need to know

um so one way that i like to remember the

the

zinc is going to make a two plus and

silver is going to make a one plus and

the way that i remember that is that

it's a backward staircase going down

we know from the last section that

aluminum is a plus three

so it's a three two one so aluminum is a

plus three

zinc is a two plus and then silver tends

to make a one plus

um so those are the only ones that are

commonly known but the rest of them will

uh will will either give you the charge or

give you some other information about

them and then real briefly the inner

transition metals or the

lanthanide and actinide series that's

your f block

they will often form three plus

ions they tend to lose both of their s

electrons and then one

either f d electron um this happens

because when you have

uh when you're when your valence shell

is is this high in energy

uh it's um it's hard to tell the

difference between all the orbitals the

the energy levels are actually quite

quite close together um and so we're not

really going to deal with these we don't

really deal with these in gen chem very

much but uh it's good to know that they

do tend to form

all right and then the last thing we're

going to talk about is the electronic

structure of

anions so anions are usually non-metals

um they are um you know they're

they're these guys right these are these

are the guys that are going to tend to form

form

our anions and uh

if they follow the same principles um

the full shell is going to be

in general more stable and these ones

though when they're forming anions they

are gaining electrons so rather than

losing electrons all the way down to the

the last noble gas um they're actually

going to gain enough electrons to

uh to have the same uh electron

configuration as the noble gas at the

end of their row

uh or that full valence shell so for

example oxygen

oh sorry got a cat in my lap

for example oxygen uh is gonna often

form a

two minus ion uh and it will have the

same electron configuration as neon

so let me just show you that so oxygen

the electron configuration of oxygen is 1s2

1s2

2s2 2p4

um i can write that with helium but i'm

just going to do it longhand because

it's not very long and it tends to make the

the

two minus anion which means it's gained

two electrons

and we just stick them straight in the last

last

orbital that isn't full so uh the

valence or the electron configuration

for this

um oxide ion is going to be 2s2

and then 2p6 which

is equivalent to the electron configuration

configuration

of neon which has that full

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Chapter 4.1b Charges of ions