1.3.4 Bonding & Physical Properties

Question 1

What type of crystal structure do compounds made of metals & non-metals form?

Answer 1

ionic lattice

Question 2

Explain why ionic lattices have high melting points.

Answer 2

→ strong electrostatic forces of attraction
→ between oppositely charged ions
→ require lots of energy to overcome

Question 3

Explain why boiling points of group 6 (covalent) compounds increase down the group. e.g. from H₂S to H₂Te

Answer 3

→ going down, the no. of electrons increase
→ generates bigger temporary dipoles
→ stronger VDW forces

Question 4

Why can metals conduct electricity?

Answer 4

• metallic bonding contains delocalised electrons

- these can move around & carry a charge throughout the structure

Question 5

Explain, in terms of the intermolecular forces present in each compound, why HF has a higher boiling point than HCl.

Answer 5

HF = hydrogen bonding
HCl = (permanent) dipole-dipole bonding
hydrogen bonding is stronger

Question 6

State the meaning of the term electronegativity.

Answer 6

the power of an atom to attract the electron

density in a covalent bond towards itself

Question 7

Explain how the hydrogen bonding arises between two molecules of ammonia.

Answer 7

• large electronegativity difference between N & H
• this creates dipole with 𝛿− N & a 𝛿+ H
• there is an attraction between the lone pair on N & the 𝛿+ H

Question 8

Why is ice less dense than water?

Answer 8

molecules in ice are held further apart than in liquid water due to an extra hydrogen bond

Question 9

Describe the bonding in a metal.

Answer 9

in metallic bonding:

• strong electrostatic forces of attraction between
• positive ions (cations)
• & delocalised electrons

Question 10

Explain why magnesium has a higher melting point than sodium.

Answer 10

• Mg is smaller ion
• with more protons (higher nuclear charge)
• so stronger attraction to delocalised electrons
• metallic bonding is stronger than in Mg

Question 11

Why do diamond and graphite both have high melting points?

Answer 11

• both are giant covalent structures (macromolecular)
• with strong covalent bonds
• that require lots of energy to overcome/break

Question 12

Why is graphite a good conductor of electricity?

Answer 12

• contains delocalised electrons
• that can move & carry a charge through the structure

Question 13

Why is graphite soft?

Answer 13

• layers with weak VDW forces between them

- this allows the layers to slide over each other

Question 14

Explain why the O–H bond in a methanol molecule is polar.

Answer 14

• oxygen is more electronegative than hydrogen
• electrons drawn towards oxygen
• causes higher e– density round oxygen
• forms a polar bond as H is δ+ & O is δ–

Question 15

Deduce why the bonding in nitrogen oxide is covalent rather than ionic.

Answer 15

Small electronegativity difference

Question 16

In terms of atomic structure, explain why the VDW forces in liquid argon are very weak.

Answer 16

• argon particles are single atoms with electrons closer to nucleus
• cannot easily be polarised

Question 17

In terms of structure and bonding, explain why sulfur has a higher melting point than phosphorus.

Answer 17

• sulfur molecules (S₈) are larger than phosphorus (P₄)
• stronger VDW forces between S₈ molecules
• more energy required to overcome these

Question 18

In terms of intermolecular forces, suggest the main reason why phosphine is almost insoluble in water.

Answer 18

• phosphine does not form hydrogen bonds with water

- difference in electronegativity between P & H is too small

Question 19

Van der Waals’ forces exist between all molecules.

Explain how these forces arise.

Answer 19

• random movements of electrons generates a temporary dipole
• induces temporary dipoles in neighbouring molecules
• δ+ end of one dipole attracts δ- in different molecules

Question 20

Describe the structure and bonding of iodine.

Answer 20

→ solid lattice of I2 molecules held together by weak intermolecular forces

Question 21

Describe the diagram used to represent the structure of ice.

Answer 21

→ tetrahedral with central water molecule
→ two H bonds from the lone pairs on oxygen
→ one H bond from each H atom