Determine the oxidation number of each element in the...

Key Concepts

Oxidation Number

The oxidation number (or oxidation state) is a theoretical charge assigned to an atom in a compound, assuming that all bonds are 100% ionic. It helps in keeping track of electrons during chemical reactions, especially redox reactions, by providing a systematic method to identify how electron density is distributed among the atoms in a molecule or ion.

Rules for Assigning Oxidation States

A set of conventions is used to assign oxidation numbers. Key rules include: elements in their elemental form have an oxidation number of zero; for a compound, the sum of all oxidation numbers equals zero; for a polyatomic ion, the sum equals the charge; common oxidation states for certain elements (like oxygen is usually -2 and hydrogen is usually +1) are taken into account; and more electronegative atoms in a bond are assigned electrons in oxidation number calculations.

Electronegativity and Its Role in Oxidation Number

Electronegativity, the tendency of an atom to attract electrons, plays an important role in determining oxidation states. In a bond between two atoms, the more electronegative atom is considered to attract the shared electrons more strongly, which influences its assigned oxidation number. This concept helps to rationalize the standard oxidation number values assigned to elements in different chemical environments.

Oxidation States in Polyatomic Ions

For polyatomic ions, the oxidation numbers of all atoms are calculated such that their sum equals the overall charge of the ion. This requires consideration of all known standard oxidation numbers and careful distribution of the remaining charge among the other atoms, ensuring that the total matches the ion's net charge.

Transcript

00:01 Hello, we're going to talk about assigning oxidation numbers.

00:05 I've written a very, very abbreviated set of rules.

00:09 For a pure element, the oxidation number is always zero.

00:15 The monotomic ions, the oxidation number is the charge.

00:20 When fluorine is combined, it's always negative 1.

00:24 When oxygen is combined, it's mostly negative 2, unless with fluorine, then it's positive.

00:31 Or a peroxide, it's negative one, or a superoxide, it's negative one -half.

00:40 Let's see here.

00:43 And next we have chlorine, bromine, and iodine.

00:46 They're negative one, except when they're with oxygen or fluorine.

00:50 Hydrogen is usually a plus one, except when it's a metal hydride, and it's negative one.

00:55 The algebraic sum of a molecule or formula unit of a compound is zero.

01:01 And the algebraic sum of an ion is the ion.

01:05 Let's practice.

01:09 I'm going to go to a little darker color.

01:12 For our first substance, we're going to look at b .r .o .3 with a negative one charge.

01:23 So we're going to figure out the charge for bromine and the charge for oxygen.

01:28 Oxygen is negative 2 because it's negative 2 just because we know that it is not a peroxide or superoxide and it's going to be a negative 2.

01:41 We have an overall charge on our ion of a negative 1.

01:47 So this has to be a plus 5 because if i add these two numbers, i get a negative 1, which is the charge of the ion.

01:56 So on these two substances, bromine is a plus 5.

02:00 Oxygen is a minus 2.

02:02 Let's do another.

02:05 Next we have c2, 04 with a 2 minus 2.

02:11 Charge.

02:13 So i have c and o.

02:17 Again, oxygen is going to be a negative 2.

02:19 And if i take negative 2 times 4, i get a negative 8.

02:23 What does the charge on our carbon have to be in order to have a negative 2 as the algebraic sum of these two substances? it needs to be plus 6...

Please give Ace some feedback