Chemistry - Structures and Properties

Question 1

What is the melting and boiling point of ionic compounds?

Answer 1

• Very high melting and boiling points (solids at room temp)
• There is strong mutual electrostatic attraction between oppositely charged ions

Question 2

What is the hardness of ionic compounds?

Answer 2

• Tend to be hard, as attractive forces cause the ions to resist motion
• When enough force is applied, the ions move away from lattice positions –> ions of same charge approach each other –> repulsive force overcomes attractive force –> structure shatters
• Hard but brittle

Question 3

What is the solubility of ionic compounds?

Answer 3

Some are soluble in water, insoluble in organic solvents. Dissolved in water –> aqueous

Question 4

What is the electrical conductivity of ionic compounds?

Answer 4

When the compound is molten/aqueous, the IONS are mobile and can conduct electricity. Cannot conduct in solid state –> not mobile

Question 5

What are the structural properties of simple covalent molecules?

Answer 5

Atoms in molecule held by strong covalent bonds. Molecules held by weak intermolecular forces of attraction. Form lattices at low temperatures.

Question 6

What is the melting and boiling point of simple covalent molecules?

Answer 6

Low melting and boiling points. Some are volatile. Weak intermolecular forces of attraction are easily overcome (overcome during boiling) with a small amount of energy.
Larger molecule –> higher melting + boiling points

Question 7

What is the solubility of simple covalent molecules?

Answer 7

Insoluble in water, soluble in organic solvents.

Question 8

What is the electrical conductivity of simple covalent molecules?

Answer 8

Usually exist as neutral molecules, no mobile charge carriers. However, some dissolve in water and become an electrical conductor.

Question 9

What are allotropes?

Answer 9

Different forms of the same element with different structural arrangements of atoms.

Question 10

What is the structure of diamond, graphite and silicon dioxide?

Answer 10

Diamond: Each carbon atom bonds with four others. 3D network structure in a tetrahedral arrangement.
Graphite: Each carbon atom bonds with three others. Layered structure of hexagonal rings of carbon atoms.
Silicon Dioxide: Silicon:Oxygen –> 1:2

Question 11

What are the structural properties of graphite?

Answer 11

Strong covalent bonds within layers, weak intermolecular forces of attraction between the layers.

Question 12

What is the hardness of diamond and graphite?

Answer 12

Diamond is hard. Large amount of energy required to break structure apart.
Graphite is soft and slippery, the layers can slide over each other easily.

Question 13

What is the melting and boiling point and solubility of giant covalent structures?

Answer 13

Resistant to heat due to numerous bonds. Large amounts
of energy are required to break the strong covalent bonds within the molecule. Solids at room temperature, high melting and boiling points.
Insoluble in water and organic solvents.

Question 14

What is the electrical conductivity of giant covalent structures?

Answer 14

Those will no electrons, e.g. diamond and silica, are insulators. However, each carbon atom in graphite is bonded to three others, leaving one unbonded electron per atom, which is free and mobile and can conduct electricity.

Question 15

What are macromolecules?

Answer 15

Polymers are macromolecules –> consists of many covalent molecules joined together into chains of much larger molecules.

Question 16

What is the melting and boiling point, solubility and electrical conductivity of macromolecules?

Answer 16

Range of sizes, hence no fixed points. Typically soften over a range of temperatures when weaker intermolecular forces of attraction are overcome by the molecular vibrations with higher kinetic energy.
Insoluble in water, soluble in organic solvents.
Most do not conduct electricity.

Question 17

What is the structure of metals and alloys?

Answer 17

Metals in in the solid state have strong metallic bonds. Alloy formed when mixed with one or more others elements.
Irregular lattice arrangement in alloys –> difference in properties between alloys and pure metals

Question 18

What are the structural properties of metals and alloys?

Answer 18

Metals
- Layers in pure metals can slide over each other easily if enough force is applied.
- Malleable (flattened easily when hammered)
- Ductile (pulled into wire without breaking)
The sea of delocalised electrons hold the metal ions together.
- Alloy –> atoms of diff sizes –> irregular lattice arrangement –> larger force needed –> harder and stronger

Question 19

What is the melting and boiling point and electrical conductivity of metals and alloys?

Answer 19

Metals –> high melting and boiling points (strong metallic bonds)
Alloys –> range of temperatures
Both are good conductors of heat (electrons allow effective transfer of thermal energy) and electricity.