choose resources and process information from secondary sources to construct and discuss the limitations of models of ionic lattices, covalent molecules and covalent and metallic lattices

This model is of a metallic substance

Advantages – shows lattice structure which indicates to us that it must be hard as well as have high mp, bp. Strong electrostatic attraction shows us that it will be able to change shape (malleable + ductile).

Limitations – Doesn’t show sea of delocalised electrons which doesn’t tell us that it is a good heat and electrical conductor. Also since it doesn’t show us those electrons, we cannot tell that it is lustrous.

Na + Cl - This is a model of an ionic substance

Advantages – Shows us the simplest ration of the elements, which indicates to us that there is one sodium atom per one chlorine. Also shows us the respective charges of each of the ions in the substance, this indicates to us that it is an ionic bond due to the electrostatic bonding.

Limitations – Doesn’t show us the actual lattice structure of the substance, rather shows it as an individual molecule, which it is not. Also doesn’t show electrical conductivity in molten state.

This is also a model of an ionic substance.

Advantages – Shows us the lattice structure of an ionic substance. Shows us the charges of each ion, shows us the electrostatic bonding, shows us the ratio of ions present in the substance, shows us that it will not conduct electricity in solid state as all the ions are tightly packed in the lattice. Also since lattice (high mp, bp)

Limitations – Doesn’t show us that it will conduct electricity in molten state (when the ions are free to move).

explain the relationship between the properties of conductivity and hardness and the structure of ionic,

covalent molecular and covalent network structures.

This has already been covered in previous dot points on pages 12, 16-18. Below is a summary:

Property Metallic Crystal Ionic Crystal Covalent Network Crystal

Covalent molecular crystal

Chemical Bonding Metallic Ionic Covalent Covalent

Melting Point High High Very high Low

Electrical Conductivity

Solid: highLiquid: high

Solid: nilLiquid: high

- -

Other Properties MalleableDuctileLustrous

HardBrittle

Very HardBrittle

Soft, brittle

Examples CopperAluminium

Sodium ChlorideZinc Oxide

Silicon dioxideSilicon carbide

IceSucrose