PSc.2.2 OBJECTIVE: Understand chemical bonding and chemical interactions.


PSc.2.2.1
– Infer valence electrons, oxidation number, and reactivity of an element based on its location on the
Periodic Table.

 The outer electrons are involved in bonding.
 These are called valence electrons.

 Most stable atoms have eight valence electrons.
 When an atom has 8 valence electrons, it is said to have an octet of electrons.

 An oxidation number indicates how many electrons are lost, gained, or shared when bonding occurs.

1A
2A
 The elements in the A groups are called the representative elements .
3A 4A 5A 6A 7A
8A
0

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 4ions 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

 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 3ions 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 2ions 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 1ions 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

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)

Determine the oxidation number of each of the following elements.
a) Potassium (K) b) Chlorine (Cl) c) Tin (IV) (Sn) (4+)
(1+)
(1-)

 In general, the reactivity of metals increases from top to bottom and decreases from left to right.

 In general, the reactivity of nonmetals increases from left to right and decreases from top to bottom.