Topic 2 + 13A - Structure and bonding

Question 1

Define an ionic bond

Answer 1

Electrostatic attraction between two oppositely charged ions in an ionic compound. Formed by the transfer of electrons from one atom to another.

Question 2

What are the properties of an ionic compound?

Answer 2

• Giant lattice structure
• Conduct electricity when molten or in solution because ions are free to move and carry charge
• high melting points because of strong electrostatic forces between oppositely charge ions

Question 3

How does the charge of an ion affect melting point in ionic compound?

Answer 3

The larger the charge, the higher the charge density.
Therefore stronger forces of attraction, so more energy is required to overcome, so increased melting point

Question 4

How does the size of an ion affect melting point in ionic compounds?

Answer 4

The larger the ion, the lower the charge density.
Therefore weaker forces of attraction, less energy required to overcome forces, lower melting point.

Question 5

Explain the trend in ionic radius down a group

Answer 5

• increases down a group
• number of shells increases so valance electron further from nucleus
• increased shielding
• higher nuclear charge but this is outweighed by increased distance and shielding so ion gets larger

Question 6

Define a covalent bond

Answer 6

The linkage of two atoms held together by the electrostatic attraction between positive nuclei and the negative charge on the shared pair of electrons.

Question 7

What are the properties of diamond?

Answer 7

• giant covalent structure
• very high mpt due to strong COVALENT bonds
• does not conduct electricity as no free ions or delocalised electrons
• rigid structure allows good heat conduction

Question 8

What are the features of graphite?

Answer 8

• layers slide over each other use to weak IMF between layers
• high mpt due to strong covalent bonds
• conducts electricity due to delocalised electrons

Question 9

What is a dative covalent bond?

Answer 9

Where both the shared electrons come from the same atom.

Question 10

Using the example of ammonia, NH3, how would you answer the Q: “state and explain the shape of a molecule”

Answer 10

1. State the number of electron pairs.
   e.g. N has 3 bond pairs and 1 lone pair so 4 electron pairs.
2. State the shape this is based on and why
   e.g The electron pairs want to maximise separation to minimise repulsion so this shape is based on tetrahedral (4 electron pairs)
3. Explain lone pair repulsion
   e.g Lone pairs repel more than bond pairs which decreases the angle between the bonds.
4. State name of shape and bond angle
   e.g. the bond angle is reduced from 109.5 to 107 and the shape name is pyramidal

Question 11

Shape name and bond angle: 2 bond pairs, 0 lone pairs

Answer 11

linear, 180 degrees

Question 12

shape name and bond angle: 3 bond pairs, 0 lone pairs

Answer 12

trigonal planar, 120 degrees

Question 13

shape name and bond angle: 4 bond pairs, 0 lone pairs

Answer 13

tetrahedral, 109.5 degrees

Question 14

shape name and bond angle: 5 bond pairs, 0 lone pairs

Answer 14

trigonal bipyramidal, 90 degrees and 120 degrees

Question 15

shape name and bond angle: 6 bond pairs, 0 lone pairs

Answer 15

octahedral, 90 degrees

Question 16

shape name and bond angle: 3 bond pairs, 1 lone pairs

Answer 16

(trigonal) Pyramidal, 107 degrees

Question 17

shape name and bond angle: 2 bond pairs, 2 lone pairs

Answer 17

v-shaped/ bent, 104.5 degrees

Question 18

Define electronegativity

Answer 18

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

Question 19

Define a metallic bond

Answer 19

Electrostatic attractive force between the positively charged metallic ions and the delocalised electrons in a metallic lattice.

Question 20

Describe an experiment which can be done to prove the existence of ionic bonding

Answer 20

Electrolysis: Ions migrate to the oppositely charged electrodes. e.g. when done with copper (II) chromate (VI), the solution next to the negative electrode turns blue, and the solution next to the positive electrode turns yellow

Question 21

Name the three types of intermolecular forces

Answer 21

London forces
Permanent dipole-dipole forces
Hydrogen bonds

Question 22

How do the boiling points differ between two isomers: one branched, one unbranched (e.g. hexane vs 2,3-dimethylbutane)

Answer 22

The branched isomer has a lower boiling point because there is less surface contact between the molecules. So there are fewer London forces between the chains which take less energy to overcome compared to the straight chain.

Question 23

Why does CCl4 have a higher boiling point than CF4?

Answer 23

CCl4 has more electrons than CF4
Stronger London Forces in CCl4
Both compounds have polar bonds so there are permanent dipole-dipole forces between molecules
The dipole-dipole forces are stronger in CF4

However the London forces are stronger so CCl4 has the higher bpt

Question 24

Why does HF have a higher boiling point than HCl

Answer 24

Both have london forces - stronger in HCl as it has more electrons
Both have permanent dipole-dipole forces
HF has hydrogen bonding between molecules. Strongest IMF so takes a lot of energy to overcome so bpt higher for HF