Deck 8

Question 1

Why do ions form a giant structure?

Answer 1

Each ion attracts oppositely charged ions from all directions

• Each ion is surrounded by oppositely charged ions
• The ions attract each other, forming a giant ionic lattice

Question 2

Note:

Answer 2

All ionic compounds are solids at room temperature.

Question 3

Why do ionic compounds have high melting and boiling points?

Answer 3

A large amount of energy is needed to break the strong electrostatic forces that hold oppositely charged ions together in the solid lattice.

Question 4

Why does MgO have a higher melting point than NaCl?

Answer 4

-The charges on the Mg2+ and O2- ions are greater than Na+ and Cl-. The greater the charge, the stronger the electrostatic forces between the ions and the greater the amount of energy required to break up the ionic lattice during melting.

Question 5

Why do ions not conduct in a solid lattice?

Answer 5

• The ions are in a fixed position and no ions can move.

- The ionic compound is a non-conductor of electricity.

Question 6

Explain why an ionic compound can conduct electrcity when dissolved in water or melted.

Answer 6

• The solid lattice breaks down and the ions are free to move.
• The ionic compound is now a conductor of electrcity.

Question 7

How does water dissolve ionic compounds?

Answer 7

The polar water moleules break down the lattice by surrounding each ion to form a solution.

Question 8

Describe what happens when NaCl is dissolved in water.

Answer 8

• Water molecules attract Na+ and Cl- ions.
• The ionic lattice breaks down as it dissolves.Water molecules surround the ions.
• Na+ attracts negative charges on the oxygen atoms of the water molecules.
• Cl- attracts the positive charges on the H atoms of the water molecules.

Question 9

What sort of solvents do ions dissolve in?

Answer 9

Polar ones only.

Question 10

Define simple molecular lattice

Answer 10

A simple molecular lattice is a three-dimensional structure of molecules, bonded together by weak intermolecular forces.

Question 11

When a solid I2 changes state what happens to its bonds?

Answer 11

• The covalent bonds between them remain intact

- The weak van der Waals’ forces between the I2 molecules break.

Question 12

Why do simple molecular structures have low melting and boiling points?

Answer 12

-The intermolecular forces are weak van der Waals’ forces, so a relatively small amount of energy is needed to break them.

Question 13

Why do simple molecular structures not conduct?

Answer 13

• Simple molecular structures are non-conductors of electricity because there are no charged particles free to move.

Question 14

Why are simple molecular structures soluble in non-polar solvents, such as hexane?

Answer 14

This is because van der Waals’ forces form between the simple molecular structure and the non-polar solvent.
- The formation of these van der Waals’forces weakens the lattice structure

Question 15

Do simple molecular structures dissolve in polar solvents?

Answer 15

No

Question 16

Define giant covalent lattice.

Answer 16

A giant covalent lattice is a three-dimensional structure of atoms, bonded together by strong covalent bonds.

Question 17

Why do giant covalent structures have high melting and boiling points?

Answer 17

High temperatures are needed to break the strong covlanet bonds in the lattice.

Question 18

Why are giant covalent structures non-conductors of electricity?

Answer 18

There are no free charged particles except in graphite.

Question 19

Why are giant covalent structures insoluble in both polar and non-polar solvents?

Answer 19

• The covalent bonds in the lattice are too strong to be broken by either polar or non-polar solvents.

Question 20

What is the structure, electrical conductivity and hardness of diamond?

Answer 20

1) Tetrahedral structure
2) Poor conductivity - No delocalised electrons
3) Hard - Tetrahedral shape allows external forces to by spread throughout the lattice.

Question 21

What is the structure,electrical conductivity and hardness of graphite?

Answer 21

1) Strong hexagonal layer structure, but with weak van der Waals’ forces between the layers.
2) Good conductivity - There delocalised elctrons between laters.Electrons are free to move parallel to the layers when a voltage is applied.
3) Bonding within each layer is strong but there are weak forces between layers, allowing layers to slide easy.