Lewis Model

Question 1

Covalent bond

Answer 1

Electron pairs are shared equally between atoms

Question 2

Polar covalent

Answer 2

Electron pairs share unequally giving a polar covalent bond

Question 3

Ionic bonding

Answer 3

Electron(s) transferred from one atom to another

Question 4

Who is Gilbert Lewis?

Answer 4

Developed the theory of covalent bonding

Question 5

Lewis symbols

Answer 5

Simple way of showing valence electrons.
Simple use of electrons as dots or crosses

Question 6

Chemical bend length

Answer 6

Chemical bonds are measured using electron diffraction techniques. The length of a chemical bond is not fixed

Question 7

Lewis structure

Answer 7

Representation f the formation of covalent bonds using Lewis symbols

Question 8

Advantages and
Disadvantages of Lewis Model

Answer 8

Adv: Provides a simple way to describe bonding
Prediction of bond order
Can be extended to predict molecular shape (VSEPR)
Disadv: Doesn’t explain how bonding occurs
Doesn’t always work - many molecules don’t follow the octet rule and yet are stable.
Hypervalency
Bonding in transition metal compounds
Doesn’t explain paramagnetism of oxygen

Question 9

Electronegativity

Answer 9

The more electronegative, the more likely it will pull electrons towards it

Question 10

Octet rule

Answer 10

Atoms gain, lose or share electrons until they are surrounded by eight electrons
No vacant orbitals: no reactivity

Question 11

Exceptions to octet rule

Answer 11

• Molecules with odd numbers of electrons
• Reduced octets (i.e. less than 8 electrons)
• Expanded octets (i.e more than 8 electrons)
• Not followed usually by s- d- and f- block elements

Question 12

Octet exception - Odd number

Answer 12

O=Cl=O ->
N=O -> 9electrons
O=N=O

Question 13

Octet exception - reduced octet

Answer 13

Cl-Be-Cl ->Be has 4 electrons
BF3 ->B has 6 electrons
AlCl3 -> Al has 6 electrons

Question 14

Octet exception - Expanded octet

Answer 14

SF6 -> S has 12 electrons
PCl5 -> P has 10 electrons
IF7 -> I has 14 electrons