Structure and bonding - GCSE combined science

Why do ionic compounds conduct electricity as a liquid and when dissolved but not as a solid?

As a solid, the ions are not free to move and carry charge. In a liquid/dissolved, the ions are free to move and carry charge

Describe and explain the trend in boiling points of group 7.

Boiling points increase because the size of the molecules increases and therefore the intermolecular forces get stronger and require more energy to break.

Why do ionic compounds (eg. Sodium oxide) have high melting and boiling points?

The ionic compound has a giant ionic structure. There is a strong a electrostatic attraction between positive metal ions and negative non-metal ions in all directions. This requires a lot of energy to overcome.

Describe covalent bonding

Between non-metals.Shared pair/s of electrons between atoms.

Explain why ammonia (simple covalent molecule) has a low boiling point.

Ammonia is a simple covalent molecule with weak intermolecular forces and little energy is needed to break these.

Describe ionic bonding

Transfer of electron/s between metals and non-metals. Electrostatic attraction between oppositely charged ions. They always have a giant structure

Explain why carbon dioxide is a gas at room temperature.

Carbon dioxide is a simple covalent molecule with weak intermolecular forces and little energy is needed to break these.

Why do metals conduct electricity?

Delocalised electrons carry charge through the structure

Why do graphite and graphene conduct electricity?

Delocalised electrons carry charge through the structure

Explain why alloys are harder than pure metals.

In an alloy the atoms are of different sizes, so the layers are distorted, and therefore the layers cannot slide over each other easily

Why is graphite soft and slippery?

Only weak intermolecular forces between layers (no covalent bonds), so the layers can slide over each other easily

Name 3 giant covalent structures

Diamond, graphite, silicon dioxide (SiO2)

Explain why diamond has a high melting point.

Giant structure with only covalent bonds which are strong and therefore lots of energy needed to break them.

Describe how metals conduct thermal energy.

Delocalised electrons free to move and transfer energy through the structure

Explain why metals can be bent and shaped.

They have layers of atoms, which can slide over each other

Describe metallic bonding

Between metals.

Layers of ions surrounded by a sea of delocalised electrons. They always have a giant structure