Chapter 6 - Shapes of Molecules and Intermolecular Forces

Question 1

How does electronegativity change in the periodic table?

Answer 1

Electronegativity increases up the periodic table and across to the right.

Question 2

Rank the different bonds in their strength

Answer 2

1. Covalent bonds (strongest)
2. Hydrogen bonds
3. Permanent dipole - dipole interactions
4. Induced dipole - dipole interactions (London forces) (weakest)

Question 3

How is an induced dipole formed (London forces)?

Answer 3

1. Movement of electrons produces a changing dipole in a molecule
2. At any instant, an instantaneous dipole will exist, but its position is constantly shifting
3. The instantaneous dipole induces a dipole on a neighbouring molecule
4. The induced dipole induces further dipoles on neighbouring
   molecules, which then attract each other

Question 4

What effect is there on London forces if there are more electrons in a molecule?

Answer 4

-There will be a larger instantaneous and induced dipole
-meaning greater induced dipole - dipole interactions
-Meaning stronger London forces between molecules
-This means more energy is required to overcome the intermolecular forces so the boiling point is higher

Question 5

What is a simple molecular substance?

Answer 5

A substance made up of simple molecules , e.g H2

Question 6

What structure do simple molecules form when solid?

Answer 6

A simple molecular lattice, held together by weak intermolecular forces, but the atoms within each molecule are strongly bonded with covalent bonds

Question 7

What are the properties of simple molecular substances?

Answer 7

-Low melting and boiling point - they contain weak intermolecular forces which does not require a large amount of energy to overcome. The covalent bonds between atoms do not break as they are much stronger.
-Do not conduct electricity - there are o charged particles

Question 8

What is a hydrogen bond?

Answer 8

A type of permanent dipole - dipole interaction

Question 9

What must molecules contain in order to form a hydrogen bond with hydrogen?

Answer 9

Nitrogen
Oxygen
Fluorine

Question 10

State and explain the anomalous properties of water

Answer 10

-Solid ice is less dense than water - hydrogen bonds hold water in a lattice structure, when water freezes the water molecules become further apart. This provides an insulating layer
-High melting and boiling point - water contains both London forces and hydrogen bonding meaning a large amount of energy is required to overcome these bonds

Question 11

What is the definition for electronegativity?

Answer 11

The ability of an atom to attract electrons in a covalent bond

Question 12

What is a hydrogen bond?

Answer 12

A hydrogen bond is an attraction between a lone pair of electrons on an electronegative atom in one molecule and a hydrogen atom in another molecule attached to an electronegative atom