Intermolecular forces

Question 1

What are the 3 types of intermolecular forces?

Answer 1

London forces, permanent dipole - dipole and hydrogen bonds

Question 2

What is the order of strength of intermolecular forces?

Answer 2

London forces < permanent dipole - dipole < hydrogen bonding

Question 3

What causes London forces?

Answer 3

Electrons are constantly moving which can cause them to become asymmetrical resulting in a temporary dipole This dipole indies a dipole on a neighbouring or close atom leading to an attraction between atoms known as London forces

Question 4

How are permanent dipole - dipole forces represented?

Answer 4

With a labelled, dashed line

Question 5

What makes permanent dipole - dipole forces harder to break?

Answer 5

The larger the dipole

Question 6

How are hydrogen bonds drawn?

Answer 6

As a series of dashes between the lone pair (which must be shown) and hydrogen. Partial charges must also be shown and the two bonds on either side of the hydrogen must be drawn in a straight line.

Question 7

What do all molecules have?

Answer 7

London forces

Question 8

What molecules have permanent dipole - dipole or hydrogen bonds?

Answer 8

Polar molecules

Question 9

How does branching affect melting point?

Answer 9

It decreases the melting point

Question 10

Why does branching effect melting point?

Answer 10

The less closely the molecules can pack together due to branching, the smaller the contact area between molecules so the weaker the London forces, resulting in a lower melting point

Question 11

How does number of electrons affect melting point?

Answer 11

The more electrons a molecule has, the higher the melting point

Question 12

Why does number of electrons affect melting point?

Answer 12

The more electrons molecule has, the greater the instantaneous dipoles formed so the stronger the London forces, therefore the higher the melting point

Question 13

How do intermolecular forces effect melting point?

Answer 13

The stronger the IMF, the higher the melting point

Question 14

What is a hydrogen bond?

Answer 14

A strong permanent dipole - dipole interaction between a delta positive hydrogen on one molecules and a lone pair on a delta negative oxygen, fluorine or nitrogen on another molecule

Question 15

What are the two properties of water?

Answer 15

Solid ice is less dense than water and higher MP/BP compared to other molecules with similar numbers of electrons

Question 16

Why is solid ice less dense than water?

Answer 16

The hydrogen bonds hold the water molecules apart in an open lattice structure, causing the molecules to be further apart than in the liquid form

Question 17

Why does water have a higher MP/BP compared to other molecules with similar numbers of electrons?

Answer 17

It has 2 hydrogen bonds per molecule, plus London forces, so a lot of energy is required to overcome the bonds