Types of substance (Extended Response)

Question 1

Sodium chloride is an ionic compound produced in the reaction between sodium and chlorine.

Use the information below to explain, in terms of structure and bonding, the differences in the ability to conduct electricity.

sodium: conducts
chlorine: does not conduct
sodium chloride: does not conduct

Answer 1

(describe structure of metal, and explain the conductivity)

• sodium is a metal
• regular lattice of positively charged sodium ions
• attracted to sea of negative delocalised electrons
• electrons are free to move, so can carry electrical charge
• sodium can therefore conduct electricity

(contrast with chlorine)

• chlorine is a non-metal and a simple molecular substance
• molecules are attracted by weak intermolecular forces
• molecules are free to move, but uncharged
• there are no free, moving electrons to carry electrical charge
• chlorine does not conduct
• sodium chloride is an ionic compound
• contains oppositely charged ions held together strongly in a regular lattice
• contains charged particles, but they are not free to move, so can’t carry an electrical current
• therefore does not conduct electricity

Question 2

Mercury is a metal and paraffin oil is a simple molecular compound.
Both exist as liquids at room temperature.
Zinc chloride exists as a liquid above 290C.
Paraffin oil does not conduct electricity but the other 2 liquids do.

Explain, in terms of structure and bonding, the differences in the ability to conduct electricity.

Answer 2

• mercury is a metal
• lattice of positive mercury ions and a sea of negative delocalised electrons
• as it is liquid the lattice is not regular
• electrons are free to move
• electrons can carry electrical charge
• therefore mercury conducts electricity
• paraffin oil is a simple molecular compound
• molecules held together by weak intermolecular forces
• free to move but not charged
• can’t carry an electrical current
• therefore paraffin does not conduct electricity
• liquid zinc chloride is an ionic compound
• in a solid state it consists of a regular lattice of positive and negative ions held together by electrostatic attraction
• as a liquid the ions are free to move as the lattice is not regular, and can carry an electrical current
• therefore it can conduct electricity as a liquid