Intermolecular Forces

Question 1

What are the 3 types of intermolecular forces ?

Answer 1

Permanent dipole
Van der waals forces
Hydrogen bonding

Question 2

What are dipole forces ?

Answer 2

Polar molecules will attract other molecules with permanent dipoles.

Question 3

How are the strength of dipole forces increased ?

Answer 3

Increasing polarity if the molecules increases the strength of attraction.

Question 4

What are van der waals forces.

Answer 4

The electrons in the atoms are moving around but are never likely to be spread evenly. This gives a temporary dipole.
The dipole moment will induce a temporary dipole in a neighbouring atom by either attracting or rappelling its electron cloud.

Question 5

How is the strength of van der waals forces increased ?

Answer 5

The greater the number of electrons, the stronger the attraction and the greater the energy needed to separate out the particles.

Question 6

What would make van der walla forces very strong.

Answer 6

Atoms with many electrons have a greater attraction and therefore need a lot of energy to separate.

Question 7

What colour and substance is iodine at room temperature and pressure.

Answer 7

Greyish solid

Question 8

When is ioidine a greyish solid.

Answer 8

At room temperature and pressure.

Question 9

What colour vapour does iodine produce when heated?

Answer 9

Purple.

Question 10

Why does iodine produce a purple vapour when heated ?

Answer 10

Iodine is composed of diatomic molecules which exist in order to make a molecular crystal solids. Each molecules in independent and is only attracted by van der waals forces. This means little energy is needed to separate an iodine molecule.

Question 11

How much energy is needed to separate an iodine molecule and why.

Answer 11

Little energy because the diatomic molecules are independent and only attracted by van der waals forces.

Question 12

What type of molecules are in iodine.

Answer 12

Diatomic

Question 13

What are hydrides

Answer 13

A compound which contains hydrogen and metal.

Question 14

How does the boiling point of a hydride relate to its Molecular mass.

Answer 14

As molecule mass increases, do does boiling point.

Question 15

Why do H20, NH3 and HF all have higher boiling points than expected for their Mr ?

Answer 15

All 3 have hydrogen intermolecular bonds which are very strong and require a lot of energy to break.

Question 16

What is another name for 3-H bonds

Answer 16

Dipole-dipole bonds

Question 17

What is another name for dipole-dipole bonds ?

Answer 17

3-H bonds.

Question 18

When do 3-H bonds or dipole-dipole bonds occur ?

Answer 18

They occur when a hydrogen is bonded to nitrogen, oxygen or flouring which are all very electronegative.
The H only has 2 electrons in the covalent bond and when these are pulled away from the H atom, the H nucleus is exposed.
The H bonds is then the attraction between the lone pair in N/O/F and the slightly positive neighbouring H atom.

Question 19

What atoms create dipolar-dipolar bonds with hydrogen ?

Answer 19

Oxygen
Nitrogen
Fluorine

Question 20

What does the size of F/O and N mean for dipole-dipole bonds ?

Answer 20

They are all small atoms so lead to a high charge density which makes the internolecular attraction greater and therefore increases melting and boiling points of the molecule.

Question 21

What atoms have a high charge density and why.

Answer 21

Oxygen, fluroine and nitrogen because they are all small atoms.

Question 22

How many bonds does water have ? And what type of bonds ?

Answer 22

4 hydrogen bonds

Question 23

What formation does water have ?

Answer 23

Tetrahedral

Question 24

Why does ice float ?

Answer 24

The volume of ice is larger than water therefore meaning ice is less dense than water and will float.

Question 25

What happens to ice when it is melted ?

Answer 25

The structure of ice collapses and the molecules come closer together then move further apart as then gain more energy.

Question 26

Why does hydrogen fluoride have a high melting point.

Answer 26

Fluorine has the highest electronegativity and is small so hydrogen bonds are extremely polar.

Question 27

What is the Mr of hydrogen fluoride.

Answer 27

20