Structure and Physical Properties of Materials (D)

Question 1

How does magnesium and oxygen chemically combine to make Magnesium Oxide?

Describe ionic bonds.

Answer 1

• Each magnesium atom loses 2 electrons and transfers it to the oxygen atom.
• Each oxygen atom gains 2 electrons from the magnesium atom.
• There are strong electrostatic forces of attraction between the magnesium cation and the oxygen anion.

Question 2

How does carbon and oxygen chemically combine to form carbon dioxide?

Describe covalent bonds.

Answer 2

• Each Carbon atom shares 4 electrons oxygen. (to obtain a stable noble gas structure of neon)
• Each oxygen atom shares 2 electrons with carbon. (to obtain a stable noble gas structure of neon)
• There are strong covalent bonds formed between carbon atoms and oxygen atoms in the carbon dioxide covalent compound

Question 3

Describe the bonding and structure of an ionic compound.

Answer 3

• Has a giant ionic crystal lattice
• three-dimensional network of cations and anions
• held by strong electrostatic forces of attraction between cations and anions

Question 4

Describe the bonding and structure of a simple covalent compound.

Answer 4

• Has a simple molecular structure
• Exist as small discrete molecules(individual molecules)
• held by weak intermolecular forces of attraction between molecules

Question 5

Describe the bonding and structure of a metal.

Answer 5

• Has a giant metallic structure
• With a lattice of cations surrounded by ‘sea’ of delocalised electrons
• strong electrostatic attraction between positive ions (cations)and delocalised electrons

Question 6

Why can’t an ionic compound conduct electricity in its solid state?

Answer 6

• Ions are held in fixed positions by strong ionic bonds.
• No free moving ions to conduct electricity.

Question 7

Why can an ionic compound conduct electricity in molten or aqueous state?

Answer 7

• Giant crystal lattice structure breaks down.
• Ions are able to move freely to conduct electricity

Question 8

Why does a simple covalent compound not conduct electricity in all states?

Answer 8

• Covalent compounds exists as molecules. → No free moving ions to conduct electricity.
• All valence electrons used up for bonding. → No free moving electrons to conduct electricity.

No mobile charge carriers.

Question 9

Why can a metal conduct electricity?

Answer 9

• Presence of delocalised electrons which can move freely throughout the metallic structure (when a potential difference is applied)

Question 10

Describe the structure and bonding of a polymer.

Answer 10

• Made of large molecules / macromolecules held together by intermolecular forces of attraction
• Polymer has a bigger molecular mass than an individual molecule (Simple Covalent Substance)

Question 11

Why does a polymer have a higher m.p and b.p than an simple covalent compound?

Answer 11

• Polymer has a larger molecular mass than a simple covalent compound.
• Hence the intermolecular forces of attraction are stronger than those between molecules in simple covalent compounds

Question 12

Describe structure and bonding of silicon dioxide.

Answer 12

• Giant molecular structure consisting of a giant network of silicon and oxygen atoms in a 3D tetrahedral structures
• **Held by strong covalent bonds **between silicon and oxygen atoms

Question 13

Describe structure and bonding of diamond

Answer 13

• Giant molecular structure consisting of a giant network of carbon atoms in a 3D tetrahedral structures
• Held by numerous strong covalent bonds between carbon atoms

Question 14

Describe structure and bonding of Graphite

Answer 14

• Giant molecular structure consisting of a huge network of atoms with layers of carbon atoms
• Held by weak intermolecular forces of attraction between the layers

Question 15

Why can graphite be used as a lubricant?

Answer 15

• Layers of carbon atoms are held by weak intermolecular forces of attraction
• Layers can slide over one another easily

Question 16

Why can’t silicon dioxide and diamond conduct electricity?

Answer 16

• All the atoms are bonded to each other
• All valence electrons are used for bonding
• No free moving electrons to conduct electricity

Question 17

Why can graphite conduct electricity

Answer 17

• Each carbon atom is bonded to 3 other carbon atoms, one valence electron for each carbon atom is not used up for bonding.
• Hence, there is free moving electrons to conduct electricity that move along the layers

Question 18

What is an alloy

Answer 18

An alloy is a mixture of a metal and one or more other elements (metals or non-metals)

Question 19

Why are pure metals soft?

Answer 19

• Atoms in pure metals are of the same size and are orderly arranged.
• The layer of atoms can slide over one another when a force is applied.

Question 20

Why are alloys harder than pure metals?

Answer 20

• The atoms of different elements have different sizes.
• This disrupts the orderly arrangement of pure metal atoms
• Makes it much harder for the layers to slide over one another.