Need up to 30 seconds to load.

in this video we're going to go over

oxidation numbers and how to find it so

let's say if we're given the element in

zinc what is the oxidation number of

zinc now the first rule that you need to

know is that the oxidation state of any

pure element is always zero so the

oxidation state of oxygen gas as a pure

element is zero fluorine gas as the pure

element is zero even

phosphorus as a pure element is zero so

there's no charges and it's only one

pure element is not a compound the

oxidation state will always be zero so

that's the first rule you need to keep

in mind now the second thing is the

oxidation state of ions the oxidation

state of the zinc two plus ion is

basically the charge of what you see

there it's positive two the oxidation

state of the Fe plus three I am is

simply positive three now sometimes you

might have diatomic ions for example the

mercury two plus ion individually each

mercury ion has an oxidation state of

one because there's two of them so you

need to write an equation Q mercury

Adams has a net charge of positive two

so if you divide both sides by two you

can get the individual oxidation state

of each mercury particle which is plus

one so there's another example this is

the peroxide ion to find the oxidation

state of each oxygen atom in this ion

you can write an equation is two oxygen

atoms with the total charge of negative

two so individually each oxygen atom has

a charge of minus one so that's the

oxidation state of oxygen individually

in the peroxide honor

this is the superoxide iron so if you

want to find the oxidation state you

need to divide the total charge by two

so each oxygen atom has a net charge of

negative 1/2 so two of them combined

will have a net charge of negative one

so keep this in mind anytime you have a

pure element the oxidation state will

always be zero and if you have an ion

let's say if it's a mono atomic ion the

oxidation state is the same as that ion

now let's talk about compounds whenever

you have fluorine inside a compound when

it's not a pure element fluorine is

always going to have a negative 1

oxidation state fluorine is the most

electronegative element when oxygen is

in a compound it's going to have a

negative 2 oxidation state unless it's

bonded to fluorine or unless you hear

the name peroxide or superoxide whenever

you hear the name peroxide oxygen has a

negative 1 oxidation state if you hear

the word superoxide it has a negative

1/2 oxidation state if you hear the word

oxide then the oxidation state is

negative 2 which is 9 at the seventh

time now hydrogen will have an oxidation

state of plus run when bonded to a

nonmetal

when bonded to a metal hydrogen will

have an oxidation state of negative one

and really the key is electronegativity

hydrogen is more electronegative than

most metals that's why it bears a

negative charge but hydrogen is usually

less electronegative and then most

nonmetals and so that's why there's a

positive charge so typically the element

that's more electronegative is the one

that usually carries the negative charge

now let's work on some examples

what is the oxidation state of magnesium

and chlorine in this compound by the way

most halogens are usually negative one

chlorine technically has a negative one

charge like fluorine if we write an

equation mg plus 2cl

this whole compound is neutral so

therefore the total charge is zero

now if chlorine has a negative 1

oxidation state that means magnesium has

to have a positive 2 oxidation state you

can literally solve it and it makes

sense magnesium is an alkaline earth

metal which typically has a positive 2

charge go ahead and find the oxidation

states of aluminum and fluorine in this

example well we know that fluorine is

negative 1 in a compound

always an aluminum based on where it's

located in a periodic table it's

typically positive 3 within an ionic

compound and you could solve it to Al

plus 3 F should add up to 0

because then that charge is 0 so each

fluorine atom has an oxidation state of

negative 1 so now we got to add 3 to

both sides so aluminum has an oxidation

state of positive 3

is another example find the oxidation

state of vanadium and oxygen and is

kapha so this is called vanadium oxide

so whenever you hear the word oxide

oxygen has a negative two charge so we

got two vanadium atoms plus five oxygen

atoms with a net charge of zero so each

oxygen atom has an oxidation state of

negative 2 5 times negative 2 is

negative 10 and then add 10 to both

sides so 2 V is equal to 10 next divide

both sides by 2 so 10 divided by 2 is 5

and so the oxidation state of vanadium

is positive 5 now let's go over some

examples

containment polyatomic ions consider

sulfate what is the oxidation state of

sulfur and sulfate well no oxygen is

usually negative 2 so let's write an

equation sulfur plus 4 oxygen atoms has

a net charge of negative 2

so each option atom has an oxidation

state of minus 2 and 4 times negative 2

that's negative 8 next we need to add 8

to both sides negative 2 plus 8 is

positive 6 so this is the oxidation

state of sulfur and sulfate let's look

at another example phosphate go ahead

and find the oxidation state of

phosphorus in phosphate so once again

oxygen is still negative 2 so we got a

phosphorus atom plus 4 oxygen atoms and

then that charge is negative 3 based on

what we see here so it's going to be P

plus 4 times negative 2 and 4 times

negative 2 is negative 8 and then add 8

to both sides so negative 3 plus 8

that's going to be positive 5 and that's

the oxidation state of phosphorus

let's look at another example let's try

Nightrain and also glory as perchlorate

go ahead and find the oxidation state of

nitrogen and chlorine in these two

pilots Emig ions so we have a nitrogen

three oxygen atoms and that's going to

equal in that charge of negative one so

always negative 2 3 times negative 2 is

going to be negative 6 and negative run

plus 6 if we add 6 to both sides that's

going to be positive 5

so that's the oxidation state of

nitrogen and for chlorine in per

chlorine it's going to be CL plus 4

oxygens equals in that charge of

negative 1 so this is going to be 4

times negative 2 which is a negative 8

and then negative 1 plus 8 that's going

to give us an oxidation state of

positive stuff so now I know how to find

the oxidation states of elements within

compounds and polyatomic ions now I want

you to understand the concept of

electronegativity and how it relates to

oxidation numbers electronegativity

increases towards fluorine on a periodic

table so as you go up into the right the

electronegativity increases so let me

give you some values of common elements

so let's say hydrogen is somewhere in

the corner over there and then we have

boron carbon nitrogen oxygen fluorine

chlorine bromine iodine phosphorus and

sulfur hydrogen has an electronegativity

value of 2.1 for boron is 2.0 carbon is

2.5 and then 3.0 3.5 floorings the

highest is 4.0 phosphorus it's two point

one is the same as hydrogen sulfur is

2.5 chlorine the street for no

and this is 2.8 iodine is 2.5 so keep

these values in mind so here's a

question for you

what is the oxidation state of oxygen

and flowing in oxygen difluoride now

oxygen has an electronegativity value of

3.5 fluorine is 4.0 so which one is more

electronegative electronegativity is the

ability of an atom to attract electrons

to itself so flowing is going to pull on

electrons in this molecule it's going to

have a stronger Pole than oxygen so

flowing is going to acquire a partial

negative charge whereas oxygen is

therefore going to acquire a partial

positive charge because fluorine pulls

on the electrons stronger than oxygen

can so in this example oxygen will not

have its typical charge of negative 2

the only time oxygen will have its

oxidation state of negative 2 is if it's

the most electronegative element in that

compound if it's not then it's going to

have a positive oxidation state keep in

mind any time flame is in the compound

it has an oxidation state of negative 1

and the reason for that is because

fluorine is the most electronegative

element on a periodic table so now we

can solve for oxygen so o plus 2 F

should have a net charge of zero because

there's no number here so fluorine is

negative 1/2 times negative 1 is

negative 2 so if we add 2 to both sides

oxygen is going to equal positive 2

which makes sense because it's partially

positive in this particular example

now let's look at two other examples

hydrochloric acid and sodium hydride

chlorine has an electronegativity value

of 3.0 hydrogen is 2.1 and sodium it's

like 1 point something I'm not sure what

the exact number is it could be like 1.5

1.7 but I know it's less than 2 so in

this example hydrogen there's a partial

positive charge chlorine there's a

negative charge because chlorine is more

electronegative than hydrogen so

therefore chlorine is going to have its

oxidation state of negative 1 which is

typical of most collisions hydrogen is

going to have an oxidation state of plus

1 as you mentioned before whenever

hydrogen is bonded to a nonmetal the

oxidation state is usually positive 1

now what about in sodium hydride well we

know that sodium is an alkali metal

which always have a positive run charge

so therefore sodium is going to have an

oxidation state of +1 but hydrogen has

an oxidation state of negative 1

typically when hydrogen is bonded to a

metal it usually has a negative Run

oxidation state and it makes sense

because hydrogen is more electronegative

than most metals so it usually bares the

partial negative charge that's why it

has a negative oxidation state sodium

has the positive charge still it has a

positive oxidation state and so you can

use electronegativity to help you

determine what the oxidation state will

be so let me give you another example BH

Stream

what is the oxidation state of boron and

hydrogen feel free to try that one now

hydrogen has an electronegativity value

of 2.1 and boron is 2.0 now as boron a

metal or nonmetal in this example

hydrogen is more electronegative so

hydrogen bares the partial negative

charge or boron bears the partial

positive charge so therefore hydrogen

it's going to have its oxidation state

of negative one because it's more

electronegative than boron so then this

is going to be B plus 3 H which is equal

to zero so 3 times negative 1 is

negative 3 so boron is going to have an

oxidation state of positive 3 in this

example now let's consider these two

examples so Furyk acid or rather

hydrofluoric acid and also sulphur

dioxide now hydrogen has an en value of

2.1 sulphur is 2.5 an oxygen is 3.5 so

in sulphur dioxide oxygen has the

partial negative charge sulphur has the

partial positive charge now in h2s

hydrogen has the partial positive charge

sulphur has the function negative charge

9 a periodic table we have elements like

nitrogen oxygen fluorine typically

nitrogen has a negative 3 charge oxygen

- 2 fluorine negative 1 so for 2 sulfur

usually has a negative 2 charge if if

sulfur is the more electronegative

element so looking at h2s hydrogen is

brought in to a nonmetal that is more

electronegative than itself so hydrogen

is going to have the positive 1

oxidation state and there's two of them

so sulfur in this example has its normal

oxidation state of negative 2

so you can base your answer on a

periodic table if sulfur is the more

electronegative element now in so2 you

can't do that because sulfur doesn't

have the partial negative charge so you

can't based a charge on a periodic table

you can do so however for oxygen because

oxygen is the electronegative element in

that compound so you can use the

negative two charge for oxygen so oxygen

is going to have an oxidation state of

minus two and to find it for sulfur it's

going to be s plus two oxygen atoms

equals zero so that's 2 times negative 2

which is negative 4 so sulfur is going

to have a positive oxidation state of 4

due to the positive partial charge so

elements that are less electronegative

typically those are the ones you got to

solve for the ones that are more

electronegative you can find a charge

based on a periodic table if they carry

a negative charge now let's look at some

other examples nh3 and no2 go ahead and

find the oxidation state of each element

now in ammonia hydrogen has an en value

of 2.1 but nitrogen is more

electronegative

it's 3.0 so therefore nitrogen should

have its normal charge of negative 3 if

we write an equation n plus 3 H is equal

to 0 hydrogen is going to have a

positive run charge it's partially

positive whereas nitrogen is partially

negative so typically when hydrogen is

bonded to a nonmetal it's usually +1

which means n has to be negative 3 so as

you can see nitrogen is the

electronegative element in this example

and it has its periodic charge of

negative 3 which you can find out in

periodic table now in this case o is

more electronegative so nitrogen is

going to have a different oxidation

state it's not going to be its natural

oxidation state of negative 3

so in this example it's going to be

positive for typically when you have

elements like nitrogen sulfur phosphorus

if they carry and the element that's

more electronegative than itself those

are the elements together solve for the

one that usually has a partial positive

charge now try these two examples

methane and the carbon dioxide and

methane hydrogen has a positive one

charge hydrogen is less electronegative

than carbon so it's going to be

partially positive carbon is going to be

partially negative so solve them for

carbon we have C plus 4-h is equal to

zero so that's 4 times 1 so C is

negative 4 so when carbon is bonded to

hydrogen carbon has a negative oxidation

state when carbon is bonded to oxygen

it's going to have a positive oxidation

state when it's bonded to hydrogen it

has a negative oxidation state so oxygen

is negative 2 and there's two of them so

carbon is going to have to be positive 4

in this example now sometimes you might

have elements that have an average

oxidation state that's not a whole

number let's try these two c3h8 and

fe3o4

in this example hydrogen is less

electronegative than carbon so it's

going to be positive 1 so if we write

the formula 3 C + 8 H it's equal to zero

so that's going to be 8 times 1 and if

we subtract 8 from both sides 3 C is

equal to negative 8 so carbon on average

has an oxidation state of negative 8

over 3 now let's do the same thing for

fv304 so we got 3 iron atoms and 4

oxygen atoms within that charge of zero

so oxygen has an oxidation state of

negative 2 so 4 times negative 2 that's

negative 8 and if we add 8 to both sides

when you get this so Fe has an oxidation

state of 8 over 3

so 8 over 3 is about 2.67 now keep in

mind an individual iron atom cannot have

a charge of 2.67 it's usually a whole

number like positive 2 or positive 3

because electrons and protons there they

basically have numerical charges an

electron has a charge of negative 1 a

proton has a charge of positive 1 so a

typical ion will have a decimal charge

so what does it mean that the average

oxidation state is 2 point 6 7 so what

is meant by that in this compound there

are three are in ions and four oxygen

ions each oxygen has a charge of

negative two so the total negative

charge is negative 8 in order for the

compound to be electrically neutral the

total positive charge has to be positive

8 iron metal has two common oxidation

states positive 2 and positive 3 now

they all can't be positive 3 because 3

plus 3 plus 3 is 9 and they can't all be

positive 2 because 2 plus 2 plus 2 is 6

so some of them is positive 2 and some

are positive 3 so the question is how

many iron ions to have a +2 charge and

how many have a +3 charge in order to

get up to eight two of them has to have

a positive 3 charge and one of them has

to have a positive 2 charge if you

average the numbers 2 3 and 3 and

divided by 3 that's going to be 8 over 3

which averages out to 2 point 6 7 so

whenever you get a decimal value what it

really means is that that's the average

oxidation state individually some more

positive 3 and some are positive 2 so

the individual ions should have a

numerical oxidation state so when you

have multiple of them the average could

be a

no value because these they don't all

have to be the same they can be

different so hopefully this makes sense

in terms of why some oxidation states

have a decimal value now let's try the

polyatomic ions that have three

different elements in it go ahead and

find the oxidation state of every

element in that polyatomic ion so oxygen

has an oxidation state of negative two

hydrogen is positive one when it's

bonded to nonmetals so usually so all

we're going to do is find sulphur so H

plus s plus three oxygen atoms as in

that charge of negative one so hydrogen

is one oxygen is negative 2 and so 3

times negative 2 that's negative 6 and

then 1 plus negative 6 is negative 5 so

now let's add 5 to both sides

negative one plus five is positive four

so in this example sulfur has an

oxidation state of positive four go

ahead and try this one k2 cro4 find the

oxidation state of every element in that

example so we have two potassium atoms a

chromium atom and four oxygen atoms now

we know oxygen is going to have an

oxidation number of negative two

potassium is an alkali metal which all

of them have a positive one charge

chromium is the transition metal and it

has a variable charge so that's what I'm

going to solve for so this is going to

be 2 times 1 plus CR plus 4 times

negative 2 and all of that is equal to 0

so 4 times negative 2 that's negative 8

and 2 plus negative 8 is negative 6 so

therefore in this example chromium has

an oxidation state of positive 6

try this one potassium bicarbonate find

the oxidation state of carbon in this

example so we know oxygen is going to be

negative to potassium and alkali metal

is plus 1 and hydrogen hydrogen is

actually bonded to the oxygen in

bicarbonate if you were to draw the

Lewis structure

so therefore hydrogen is bonded to a

nonmetal through a covalent bond and so

it's going to be plus 1 so we have K

plus h plus c plus 3 o and that's equal

to 0 so K is positive 1 hydrogen is 1 an

oxygen is going to be 3 oxygen is

negative 2 but we're going to multiply

that by 3 so 1 plus 1 is 2 3 times

negative 2 is negative 6 and then 2 plus

negative 6 that's negative 4 so in this

example carbon is positive for potassium

bicarbonate you could break it up into

two ions k+ and hco3 minus so just by

looking at k+ that tells you that cain

has an oxidation state of positive 1 now

bicarbonate is basically the sum of the

hydrogen ion and the carbonate ion so

therefore you can see that hydrogen in

this example also has a positive one

charge and then from this you can find

the oxidation state of carbon you can

say c plus 3 own has in that charge of

negative 2

then you have to add six to both sides

so negative two plus six is positive

four so if you understand the ions and

all the polyatomic ions you can break it

down and efficiently to see that

hydrogen has a positive one charge in

this example and the same is true for K

so that's why it's good to know the

polyatomic ion Chi now have two more

examples fully BR CL 3 and IBR 5 find

the oxidation state of every element in

this example

so most halogens like fluorine chlorine

bromine iodine they typically have a

negative 1 charge but both bromine and

chlorine can't be negative so which one

is negative and which one is positive

keep in mind bromine has an

electronegativity value of 2.8 chlorine

is 3.0 iodine is 2.5 so in this example

chlorine bears the partial negative

charge bromine is partially positive so

therefore chlorine is going to have its

natural oxidation state of negative 1

bromine we need to calculate it so it's

going to be BR plus 3 CL and that's

equal to 0 so this is going to be 3

times negative 1 and so we can see that

bromine has an oxidation state of

positive 3 now in the second example

bromine is going to carry the partial

negative charge

iodine carries the partial positive

charge if it's written correctly

usually the electropositive element is

written first

the electronegative element is there in

second so the one that you see on the

right side is usually the one that

carries the natural charge that can be

found on the clear example so in this

case bromine is going to have its

natural oxidation state of negative 1

so iodine it's going to have an

oxidation state of positive five in this

example

so hopefully you understand the

relationship between electronegativity

and oxidation numbers so that's it for

this video thanks for watching and have

a good day