1.5 - Solid Structures

Question 1

What is the crystal coordination number of NaCl - Why?

Answer 1

6,6
Each Na+ is surrounded by 6 Cl- ions and vice versa

Question 2

What is the crystal coordination number of CsCl - Why?

Answer 2

8,8
Each Cs+ is surrounded by 8 Cl- ions and vice versa

Question 3

Why is there a difference in crystal coordination numbers between CsCl and NaCl

Answer 3

Cs+ ion is larger than the Na+ ion -
Therefore more Cl- ions can fit around the Cs+ ion

Question 4

What kind of structure is NaCl and CsCl

Answer 4

Giant Ionic

Question 5

What are the Physical Properties of Giant Ionic Structures - Why?

Answer 5

HIGH MELTING POINT - Lots of strong ionic bonds which require high heat energy to break.
INSULATING - Cannot conduct when solid, no mobile ions or electrons
CONDUCTS WHEN MOLTEN OR AQUEOUS - Ions become mobile
HARD but BRITTLE - Ions can repel shattering the structure
SOLUBLE - Dissolves in water as the hydration energy of the ions is larger than the lattice energy.

Question 6

Why are Giant Ionic Structures Soluble?

Answer 6

SOLUBLE - Dissolves in water as the hydration energy of the ions is larger than the lattice energy.

Question 7

Properties of graphite

Answer 7

High Melting Point - Strong covalent bonds between carbons in the layers, high energy to break
LUBRICANT - Weak Van der Waals allow the layers to slide over eachother.
CONDUCTOR - Delocalised electrons are free to move along the layers, so can carry current.
DENSITY - Low density, there is relatively large amount of space between layers. Covalent bonds are much shorter than the Van der Waals forces

Question 8

Name 5 carbon allotropes

Answer 8

DIAMOND
GRAPHITE
GRAPHENE
BUCKMINSTERFULLERENE
NANOTUBES

Question 9

Structures of graphite

Answer 9

• Layers of Hexagonal Rings
  -Each carbon is bonded to three other carbons - The fourth electron delocalises across the layer.
  -Layers are held together by weak Van der Waal’s froces

Question 10

Structure of Diamond

Answer 10

-Each carbon is covalently bonded to 4 other carbons
- Tetrahedral shape, bonding forces are uniform throughout the structure.
-No free electrons

Question 11

Properties of Diamond

Answer 11

VERY HIGH MELTING POINT - Strong covalent bonds require very high energy to break
POOR CONDUCTOR - No free electrons or ions to carry current
VERY HARD - Due to the strength of covalent bonds and the rigidity of the 3-D structure
INSOLUBLE - No ions to attract the polar water molecules

Question 12

Intramolecular and intermolecular forces in Iodine?

Answer 12

Iodine molecules are diatomic - Held together by strong covalent bonds

Iodine molecules are bonded to eachother by weak Van der Waals forces and are arranged in a regular pattern.

Question 13

PROPERTIES OF SIMPLE COVALENT MOLECULES - i.e. Iodine

Answer 13

INSOLUBLE - Cannot form hydrogen bonds to water, therefore insoluble
LOW MELTING POINT - Weak Van der Waals forces require little heat energy to break
POOR CONDUCTOR - No free electrons or ions to carry current

Question 14

When is water at its maximum density?

Answer 14

4°C

Question 15

Why does ice float on water?

Answer 15

Ice is less dense than water and takes up a greater volume.
This is due to hydrogen bonding between water molecules.
The hydrogen bonds stay rigid when water freezes creating a large open structure.
This open structure means that ice is less dense than water and therefore floats.

Question 16

Structure of Metallic Structures

Answer 16

Metals consist of a regular pattern; a lattice of metal cations and a sea of delocalised electrons.
Metallic bonding is the electrostatic force of attraction between the positively charged nucleus of the cations and the negatively charged sea of electrons.

Question 17

Difference in structure of Sodium and Magnesium

Answer 17

Sodium only has one valence electron and magnesium has two - More electrons per atom
The 2+ charge on magnesium is greater than the + charge of sodium - Bonds will be stronger in magnesium

Question 18

Properties of metals

Answer 18

GOOD CONDUCTORS - Both when solid and molten, the delocalised valence electrons can carry current when potential difference is applied
GOOD THERMAL CONDUCTOR - Delocalised electrons can pass kinetic energy to each other
HIGH MELTING POINT - A large energy is needed to overcome the electrostatic force of attraction
Melting point is affected by the no. of delocalised electrons per atom and the charge of the positive cation
MALLEABLE AND DUCTILE - Can be bent into shape and stretched into wires
When a force is applied the layers slide over each other. The delocalised electrons move with the cation to prevent repulsion between layers.