Structure and Bonding

Question 1

What are van der waals forces?

Answer 1

Weakest type of intermolecular force
All species have this
The only force for non polar species

Question 2

How do van der waal forces come about?

Answer 2

Temporary induced dipole
Arises from an uneven distribution of the e- cloud

Question 3

What makes van der waals stronger?

Answer 3

The more e- in a species the stronger the van der waals

Question 4

What species can have dipole dipole forces?

Answer 4

Polar molecules

Question 5

How do dipole dipoles come about?

Answer 5

Attraction between a partial positive charge on one molecule and a partial negative charge on another molecule

Question 6

What forces are stronger
Dipole dipole or van der waals?

Answer 6

Dipole dipole

Question 7

What is hydrogen bonding?

Answer 7

Special case of dipole dipole force
Strongest intermolecular force

Question 8

How does hydrogen bonding come about?

Answer 8

H bonded directly to N O or F
Attraction between the delta+ H on one molecule and a lone pair on N O or F from another molecule

Question 9

What is an example of a species with hydrogen bonding?

Answer 9

Water
Ammonia
Methanol

Question 10

How does a polar bond come about?

Answer 10

Shared pair of e-
If one of the atoms is more electronegative then it will exert a greater force on the electron pair
The bond won’t be symmetric so it is a polar bond
A small difference in charge represented by a delta+ and a delta-

Question 11

Why is the melting point of I2 higher than HI?

Answer 11

Both simple molecular structure with weak im forces and covalent bonds
HI has van der waal and dipole dipole
HI is polar
Dipole dipole is usually stronger
I2 has more e- so the van der waals are stronger so therefore outweighs the dipole dipole forces