5. Structure

Question 1

Give examples of different chemical structures

Answer 1

Giant ionic lattice, metallic lattice, giant covalent, molecular covalent

Question 2

Describe giant ionic lattice structure

Answer 2

• Ions are arranged in a giant repeating pattern - a lattice

- An ionic bond which holds the ions together are strong since neighbouring ions have opposite charges

Question 3

What are the properties of ionic compounds?

Answer 3

• crystalline solids at room temp - regular lattice of +ve and -ve ions that pack closely together
• high melting/boiling point - large amount of heat energy required to separate the strong electrostatic interactions between oppositely charged ions
• conduct electricity when molten/aqueous, don’t in solid state - when melted or dissolved in water the strong electrostatic interactions are overcome and the ions are free to move and carry the current. This is due to the number of polar water molecules

Question 4

Define delocalised electrons

Answer 4

Outer electrons in metallic bonding that don’t have fixed positions but move freely

Question 5

Describe the properties of metals

Answer 5

• Malleable and ductile - if stress is applied it can change shape without fracturing as the metal ions can ‘slide’ over each other in their regular lattice layers
• hardness - metallic lattice is held together by strong forces of attraction between the metal ions and the delocalised electrons.
• melting point - high temps are needed to provide enough energy to pull an atom away from the attraction of the positive ions and delocalised electrons
• electrical conductivity - delocalised electrons can move and carry charge through the metal

Question 6

Describe the properties of molecular covalent structures

Answer 6

• usually soft and brittle - weak intermolecular forces between the molecules permit them to be separated easily
• low melting/boiling point - weak intermolecular forces mean they can be separated easily
• insoluble in water - polar liquids like water have strong attractions between water molecules. These attractions are stronger than iodine-iodine or iodine-water attractions.
• don’t conduct electricity - contain neither delocalised electrons nor ions so no particles to carry current

Question 7

Give examples of giant covalent structure

Answer 7

The allotropes of carbon - graphite and diamond

Silicon dioxide

Question 8

Describe the properties of diamond

Answer 8

• extremely hard - each carbon is covalently bonded to four others in a tetrahedral arrangement. Rigid 3D structure combined with strong covalent bond
• doesn’t conduct electricity - all electrons are strongly localised in the covalent bonds - 4 is full carbon valency

Question 9

Describe the properties of graphite

Answer 9

• acts as a lubricant - layers held with weak VdW forces can slide over each other
• conducts electricity - each carbon is covalently bonded to 3 others in a layered hexagonal structure - delocalised electrons can move and carry charge

Question 10

Give general giant covalent structure properties

Answer 10

• high melting points - large amount of energy needed to break the large number of strong covalent bonds between the atoms in a giant covalent structure. Consequently they will have very high melting and boiling points
• insoluble in water or organic solvents - bonds in a giant covalent structure are very strong and no solvent is able to break up the structure