STRUCTURES AND FORMULAS

Question 0

describe the structure of a crystal of sodium chloride (2)

Answer 0

• it is one giant ionic lattice (which is why salt crystals are usually cuboid in shape)
• the Na+ and Cl- ions are held together in a regular lattice

Question 1

list the properties of a giant ionic compound (5)

Answer 1

• strong electrostatic forces of attraction between oppositely charged ions= high melt/boil point
• when the ions can move (solid) they don’t conduct electricity/heat
• when melted/dissolved in solution the ions can move, and they then carry an electric current
• it is a giant lattice structure made up of regular lattice structures

Question 2

name the two types of covalent substances (2)

Answer 2

• simple molecular substances

- giant covalent structures

Question 3

what are the properties of a simple molecular structure (4)

Answer 3

• the atoms have very strong covalent bonds to form small molecules
• but the intermolecular forces are very weak, which means that they have very low melting/boiling points
• (the intermolecular forces are broken when melted/boiled, not the strong covalent bonds)
• do not conduct electricity because they have no ions (no electrical charge)

Question 4

what are the properties of a giant covalent structure (2)

Answer 4

• ALL atoms bonded by strong covalent bonds which gives them high melting/boiling points
• they do not conduct electricity, even when molten (except graphite) because they have no charged ions

Question 5

describe the properties of diamond (2)

Answer 5

• each carbon atom forms 4 covalent bonds in a very rigid covalent structure
• this structure makes diamond the hardest natural substance (used for drill tips)

Question 6

describe the structure of silicon dioxide (silica) (2)

Answer 6

• it is what sand is made of

- each grain of sand is one giant structure of silicon and oxygen

Question 7

describe the structure of graphite (4)

Answer 7

• each carbon atom forms only 3 covalent bonds (2 sideways, 1 vertically)
• this creates layers which are free to slide over each other, making graphite soft and slippery
• layers held so loosely they can be rubbed off on paper (pencil), this is because the intermolecular forces between layers are so weak
• the only non-metal that is a good conductor of heat and electricity, because each carbon has 1 delocalised electron

Question 8

what are the properties of a metallic structure (5)

Answer 8

• metals consist of 1 giant structure
• metallic bonds involve delocalised electrons, which is where most of its properties come from:
• the electrons are free to move=good conductors of heat and electricity
• they hold the atoms together in a regular structure because of the strong electrostatic attraction between positive and negative electrons
• they also allow the layers of atoms to slide over each other, making metals malleable

Question 9

chemical formula of ammonia

Answer 9

NH_3

Question 10

chemical formula of methane

Answer 10

CH_4

Question 11

chemical formula of hydrochloric acid

Answer 11

HCl