INTERMOLECULAR FORCES

Question 1

Intramolecular interactions

Answer 1

ionic and covalent bond.

Question 2

intermolecular interactions

Answer 2

forces of attraction between molecules.
- no transfer of electrons.
- constant and random movement of electrons.

Question 3

types of intermoleculsr forces

Answer 3

1. london forces or induced dipole or van der waals interaction.
2. permanent dipole
3. hydrogen bonds.

Question 4

london forces

Answer 4

• proposed by Fritz london.
• rather than electrons existing statically, electrons are constantly moving within clouds of charge.
• on average electron density is always symmetrical but could be there are more electrons in one side rhan the other creating a temporary dipole.

Question 5

where are london forces found

Answer 5

almost between everything in addition to intermolecular forces of attraction.

Question 6

permanent dipoles

Answer 6

permanent dipoles are attracted to the opposite charges in other permanent dipoles.

Question 7

what are dipole dipole forces

Answer 7

when induced dipole and permanent dipole are termed together.

Question 8

hydrogen bonds

Answer 8

strong permanent dipole - dipole forces of attraction

Question 9

conditions for hydrogen bonds

Answer 9

1. electron deficient hydrogen = hydrogen bonded to more electronegative element like oxygen.
2. lone pair of electrons on a highly electronegative atom.

Question 10

elements in which hydrogen bonds occur

Answer 10

nitrogen, fluorine and oxygen.

Question 11

ice is less dense than water. why

Answer 11

because hydrogen bonds formed between water molecules breaks easily in liquid due to movement of molecules. however the hydrogen bonds holds the water molecules apart in a fix position in a n open lattice so it is less dense.

Question 12

hydrogen bonds have high bp and mp. why

Answer 12

because they are much stronger than other intermolecualr forces.

Question 13

trends in bp in noble gases

Answer 13

the bp increases down the group in noble gases because there are many electrons and a temporary dipole is created due to electron distortion. so more electrons = more distortion = more surface area = stronger van der waals force = high bp.

Question 14

h20 , hf and nh3

Answer 14

have higher boiling point than other hydrides because they contain hydrogen bonds.

Question 15

h20 has higher bp than hf

Answer 15

each water molecule is involved in attraction hydrogen bonds to 4 molecules but hf and nh3 only two each.

Question 16

how does a permanent dipole force arise

Answer 16

permanent dipole forces arise when there is acharge difference between molecules. there is a slighty positive and slightly negative end.

Question 17

bp increases in alkanes

Answer 17

as a;kane chain gets longer, electron number increases , stronger van der waals force.