Structure and Properties of materials

Question 1

what are the structure of ionic substances? (2 points)

Answer 1

1.giant ionic crystal lattice structures
2. large numbers of alternating cation and anion held tgt by strong ionic bonds

Question 2

what are the physical properties of ionic substances? (4 points)

Answer 2

1. they have high melting and boiling points
2. hard but brittle
3. soluble in water and insoluble in organic solvents
4. they can conduct electricity in both the liquid and aqueous state due to the presence of mobile ions

Question 3

why do ionic substances have high melting and boiling points? (3 points)

Answer 3

made up of a giant ionic lattice held together by strong electrostatic forces between oppositely charged ions

large amount of energy is required to OVERCOME the electrostatic forces in order to separates the ions during melting or boiling

the stronger the ionic bond, the higher the melting and boiling point

Question 4

why are ionic substance hard but brittle?

Answer 4

It is hard due to the strong electrostatic forces between oppositely charged ions. resulting the structure being hard, meaning it is resistant to force or pressure.

brittle as layers of ions may shift if force is applied to the giant ionic crystal lattice structure. ions with the same charge can be forced next to each other causing like charges to repel. this may result in the structure shattering suddenly

Question 5

what are the structures of simple covalent substances? (3 points)

Answer 5

1. the atoms in simple covalent molecules are held by strong covalent bonds
2. the simple covalent molecules bonds are held tgt by weak intermolecular forces of attraction
3. in solid state, simple covalent molecules such as ice form lattice structures

Question 6

what are the physical properties of simple covalent substances? (4 points)

Answer 6

1. they have low melting and boiling points (opp from ionic)
2. larger molecule have higher melting and boiling points
3. they are insoluble in water but soluble in organic solvents (opp from ionic)
4. most are unable to conduct electricity due to the absence of mobile charge carriers

Question 7

why do simple covalent substances have low melting and boiling points? (3 points)

Answer 7

they are made up of small molecules held together by weak intermolecular forces.

These weak forces do not require much energy to overcome.

As a result, simple covalent substances are usually gases or liquids at room temperature, or solids with low melting points.

Question 8

list the covalent molecules that can dissociate in water to form a solution that can conduct electricity.

Answer 8

Hydrogen chloride

dissociates in water to form mobile H+ and Cl- ions

Question 9

what are the structural properties of giant covalent substances?

Answer 9

1. atoms in giant covalent structure are connected to one another via strong covalent bonds

Question 10

what are allotropes? (give examples)

Answer 10

different forms of the same element in the same physical state, where the atoms are arranged in different structures

example diamond, graphite and graphene are forms of carbon with different giant covalent structures.

Question 11

structures of a diamond (2 points)

Answer 11

1. each carbon atom in diamond forms covalent bonds with four other carbon atoms.
2. has a tetrahedral arrangement

Question 12

structures of graphite ( 3 points)

Answer 12

1. each carbon atom in graphite forms covalent bonds with three other carbon atoms
2. Graphite has a layered structure of hexagonal rings of carbon atoms
3. Between each layer, weak intermolecular forces of attraction are present (hard but brittle)

Question 13

physical properties of graphite

Answer 13

soft and slippery

Question 14

physical properties of giant covalent structures (4 points)

Answer 14

1. giant covalent structures have high melting and boiling points (same as ionic diff from simple)
2. large amounts of energy are required to break the strong covalent bonds
3. giant covalent substances are insoluble in water and organic solvent
   4.graphite can conduct electricity but diamond cannot.

Question 15

why can graphite conduct electricity? (4 points)

Answer 15

in graphite each carbon atom is covalently bonded to 3 other carbon atoms.
here is 1 electron in each carbon atom that is not used in bonding.

this electron is delocalised between the hexagon layers.

these delocalised electrons can conduct electricity.

Question 16

what happens to an electron when it is delocalised?

Answer 16

1. not attached to any atom or bond
2. free to move

Question 17

Properties of Metal (two main points)

Answer 17

metals are malleable ( the ability to be hammered into a shape without the metal cracking)

metals are ductile

Question 18

Properties of alloys (2 points)

Answer 18

Alloys tend to be less malleable and less ductile than the pure metals they are
made from.

Alloys are harder and stronger than pure metals.

Question 19

difference of pure metal and alloys ( 2 main points)

Answer 19

metals: only one element present, fixed melting and boiling point

alloys: more than one element present, a range of melting and boiling points

less malleable and ductile but stronger

Question 20

similarity of metal and alloys

Answer 20

both can conduct electricity

The “sea of delocalised electrons” allow them to conduct electricity.

Question 21

why are alloys stronger than metals? (2 points)

Answer 21

1. different sized atoms in an alloy disrupt the regular arrangement of metal atoms in the structure
2. distorts the layers makes it harder to slide past each other.

Question 22

why do metals have high boiling points?

Answer 22

1. have high melting and boiling points because the metal cations are held together in a lattice by strong metallic bonds

Question 23

why are metals and alloys good conductor of heat?

Answer 23

The delocalised valence electrons allow efficient transfer of thermal energy
throughout the giant metallic lattice.