oxidation number

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CHEMICAL BONDING and
CHEMICAL
INTERACTIONS
PSc.2.2 OBJECTIVE: Understand
chemical bonding and chemical
interactions.
Objectives

PSc.2.2.1
–Infer valence electrons,
oxidation number, and
reactivity of an element
based on its location on the
Periodic Table.
Bonding and Molecules
The outer
electrons are
involved in
bonding.
 These are called
valence
electrons.

Bonding and Molecules
Most stable
atoms have eight
valence electrons.
 When an atom
has 8 valence
electrons, it is
said to have an
octet of
electrons.

The Octet Rule
Oxidation Number

An oxidation
number
indicates how
many
electrons are
lost, gained, or
shared when
bonding
occurs.

1A
2A
The elements in the A groups
8A
0
are called the representative
3A 4A 5A 6A 7A
elements.
1A



Group 1A elements have one
valence electron.
They form 1+ ions after losing the
one valence electron.
1+ is referred to as the oxidation
number for Group 1A elements.

2A


Group 2A elements have two
valence electrons.
They form 2+ ions after losing the
2 valence electrons.
2+ is referred to as the oxidation
number for Group 2A elements.



Group 3A elements
have three valence
electrons.
They form 3+ ions after
losing the 3 valence
electrons.
3+ is referred to as the
oxidation number for
Group 3A elements.
3A



Group 4A elements
have four valence
electrons.
They form 4+ ions after
losing the 4 valence
electrons.
They could just as
easily form 4- ions
after gaining four
additional electrons.
4A

Group 4A elements
could have a 4+ or 4oxidation number,
depending on the
element with which
they are bonding.
4A
Group 4A
Two elements in Group 4A have
multiple oxidation numbers of 2+ and
4+.
 These two elements are tin (Sn) and
lead (Pb).




Group 5A elements
have five valence
electrons.
They form 3- ions after
gaining 3 additional
electrons.
3- is referred to as the
oxidation number for
Group 5A elements.
5A



Group 6A elements
have six valence
electrons.
They form 2- ions after
gaining 2 additional
electrons.
2- is referred to as the
oxidation number for
Group 6A elements.
6A



Group 7A elements
have seven valence
electrons.
They form 1- ions after
gaining 1 additional
electron.
1- is referred to as the
oxidation number for
Group 7A elements.
7A


Group 8A elements have eight
valence electrons, except
helium which only has 2.
Group 8A elements, with a full
complement of valence
electrons, are generally not
reactive.
8A
Question
How many valence electrons are in
an atom of each of the following
elements?
a) Magnesium (Mg) (2)
b) Selenium (Se) (6)
c) Tin (Sn) (4)
Question
Determine the oxidation number of
each of the following elements.
a) Potassium (K)
b) Chlorine (Cl)
c) Tin (IV) (Sn)
(1+)
(1-)
(4+)
Reactivity of Metals

In general, the reactivity of metals
increases from top to bottom and
decreases from left to right.
Reactivity of Metals
Reactivity of Nonmetals

In general, the reactivity of nonmetals
increases from left to right and
decreases from top to bottom.

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