Chapter 6 Shape Of Molecules And Intermolecular Forces

Question 1

bond angle

Answer 1

The angle between two bonds at an atom

Question 2

Electron pair repulsion

Answer 2

• Electron pairs repel one another so they are arranged as far apart as possible
• Lone pairs repel more strongly than bonding pairs decreasing the bond angle by 2.5

Question 3

Methane molecule

Answer 3

CH4 
4 bonded pairs
0 Lone pairs
Tetrahedral 
109.5 Bond angle

Question 4

Ammonia molecule

Answer 4

NH3
3 Bonded pairs 
1 Lone pair
Pyramidal 
107 Bond angle

Question 5

Water molecule

Answer 5

H2O
2 Bonded pairs 
2 Lone pairs
Non-linear
104.5 Bond angle

Question 6

Carbon dioxide molecule

Answer 6

CO2
2 Bonding regions
0 Lone pairs 
Linear
180 Bond angle

Question 7

Molecular shapes

Answer 7

> 2 Electron pairs/regions, 180 linear e.g CO2
3 Electron pairs/regions, 120 trigonal planar e.g BF3
4 Electron pairs/regions, 109.5 tetrahedral e.g CH4
6 Electron pairs/regions, 90 octahedral e.g SF6

Question 8

Shape of ions

Answer 8

Ammonium ion - NH4+ 4 bonded pairs 109.5 tetrahedral
Carbonate ion - CO32-, 3 bonding regions 120 trigonal planar
Nitrate ion- NO3-, 3 bonding regions 120 trigonal planar
Sulfate ion - SO42-, 4 bonding regions 109.5 tetrahedral

Question 9

electronegativity

Answer 9

A measure of the attraction of a bonded atom for the pair of electrons in a covalent bond.

Question 10

non-polar

Answer 10

With no charge separation across a bond or in a molecule.

Question 11

polar covalent bond

Answer 11

A bond with a permanent dipole, having δ+ and δ– partial changes on the bonded atoms.

Question 12

dipole

Answer 12

A separation in electrical charge so that one atom of a polar covalent bond, or one end of a polar molecule, has a small positive charge δ+ and the other has a small negative charge δ–.

Question 13

polar (molecule)

Answer 13

With δ+ and δ– charges at different ends of the molecule.

Question 14

polar molecule

Answer 14

A molecule with an overall dipole, having taken into account any dipoles across bonds and the shape of the molecule.

Question 15

permanent dipole

Answer 15

A small charge difference that does not change across a bond, with δ+ and δ– partial changes on the bonded atoms: the result of the bonded atoms having different electronegativities

Question 16

intermolecular force

Answer 16

An attractive force between molecules. Intermolecular forces can be London forces, permanent dipole-dipole interactions or hydrogen bonding.

Question 17

induced dipole–dipole interaction

Answer 17

Attractive forces between induced dipoles in different molecules – also called London Forces.

• larger numbers of electrons mean larger induced dipoles
• more energy is then needed to overcome the intermolecular forces, increasing the boiling point

Question 18

Permanent dipole–dipole interaction

Answer 18

An attractive force between permanent dipoles in neighbouring polar molecules.

Question 19

hydrogen bond

Answer 19

A strong dipole-dipole attraction between an electron-deficient hydrogen atom of –NH, –OH or HF on one molecule and a lone pair of electrons on a highly electronegative atom containing N, O or F on a different molecule.

Question 20

simple molecular lattice

Answer 20

A three-dimensional structure of molecules, bonded together by weak intermolecular forces

Question 21

Ionic or covalent (electronegativity values)

Answer 21

Electronegativity difference
0 - covalent
0-1.8 - polar covalent
greater than 1.8 - ionic