Notes – Determining Oxidation Number

Who Gains? Who Loses?

Background Information/Terms• Ion- an atom with a positive or

negative electric charge.

• Valence energy level- the outermost (highest) energy level.

• Valence electrons- the electrons found in the outermost energy level.

Background Information/Terms• Family numbers- the numbers at the top of the

periodic table that (with some modification) tell how many valence electrons an atom has.

• Octet rule- a rule (that is generally true) which states that an atom with a full valence energy level is stable.

• Oxidation number - the number of electrons that an atom gains, loses or shares in order to form chemical bonds.

Facts about Elements and Their Oxidation Number - Metals

• Metals lose their valence electrons when they become ions. This gives metals a full outermost energy level.

• Metal ions have a positive (+) charge.

• The number of electrons a metal loses becomes its oxidation number.

Facts about Elements and Their Oxidation Number - Nonmetals

• Nonmetals gain electrons until they get 8 electrons in their outermost energy level.

• Nonmetal ions have a negative (-) charge.

• The number of electrons a nonmetal gains becomes its oxidation number.

Oxidation number

• Oxidation number - the number of electrons that an atom gains, loses or shares in order to form chemical bonds.

• The oxidation number determines two things:– How the element will bond

– What elements will bond with it

Review• Elements want to have a stable atomic structure.

• Stable atoms have full outer energy levelsIf an element has only one energy level, it is full with 2 electrons

• Although the third levels hold more than 8, atoms think their energy levels are full with 8 electrons

• Some elements gain electrons to get full while other will lose electrons to empty out a level.

Summary

It is easier to gain one or two electrons than to lose 6 or 7 and vice versa.

Family # # of valence electrons

gain or lose Oxidation number

1 1 Lose 1 + 1

2 2 Lose 2 + 2

13 3 Lose 3 + 3

14 4 Gain or lose 4 +/- 4

15 5 Gain 3 - 3

16 6 Gain 2 -2

17 7 Gain 1 -1

18 8 Already full 0