2.2.2 Intermolecular Forces

Question 1

how are intermolecular forces relevant to covalent molecules

Answer 1

When you melt or boil a simple covalent substance, you only need to break the weak intermolecular forces not the strong covalent bonds.

Question 2

what are the 3 types of intermolecular forces

Answer 2

1. (induced dipole-dipole interactions) London forces
2. Permenant dipole-dipole interactions
3. hydrogen bonding

They increase in strength from London forces to hydrogen bonding

Question 3

when are each intermolecular forces revelant

Answer 3

Molecules can have more than one intermolecular force BUT we only need to consider the strongest.

Question 4

When are London forces present

Answer 4

They exist in all molecules but most importantly in non-polar molecules

Question 5

explain London forces

Answer 5

The random movement of electrons causes an ineven distrubution and a temporary dipole is formed.
This induces a dipole in a neighbouring molecule which induces a diople in another.
The interaction of the induced dipoles is the London force

Question 6

What effects the strength of London forces

Answer 6

The strength of the London forces is determined by the number of electrons

More electrons = stronger London forces = higher boiling points

eg. F2 has 18 electrons and a boiling point of -188 ℃
Br2 has 70 electrons and a boiling point of 59 ℃

Question 7

when are permenant dipole-dipole interactions present

Answer 7

They occur in polar molecules

Question 8

describe permenant dipole-dipole interactions

Answer 8

• Permenant dipoles interact to hold molecules together
• These interactions are stronger than London forces but still weaker than covalent bonds

Question 9

What effects the strength of the permenant dipole-dipole interactions

Answer 9

The bigger the dipole (the difference in electronegativity) the stronger the interaction