Ionic bonding and structure

Nature of science:

Use theories to explain natural phenomena—molten ionic compounds conduct electricity but solid ionic compounds do not. The solubility and melting points of ionic compounds can be used to explain observations. (2.2)

• Positive ions (cations) form by metals losing valence electrons.
• Negative ions (anions) form by non-metals gaining electrons.
• The number of electrons lost or gained is determined by the electron configuration of the atom.
• The ionic bond is due to electrostatic attraction between oppositely charged ions.
• Under normal conditions, ionic compounds are usually solids with lattice structures.

Applications and skills:

• Deduction of the formula and name of an ionic compound from its component ions, including polyatomic ions.
• Explanation of the physical properties of ionic compounds (volatility, electrical conductivity and solubility) in terms of their structure.

Guidance:

• Students should be familiar with the names of these polyatomic ions: NH₄⁺ ,OH^-, NO₃^-, HCO₃^-, CO₃^2-, SO₄^2- and PO₄^3-

• General rules in chemistry (like the octet rule) often have exceptions. How many exceptions have to exist for a rule to cease to be useful?
• What evidence do you have for the existence of ions? What is the difference between direct and indirect evidence?

Utilization:

• Ionic liquids are efficient solvents and electrolytes used in electric power sources and green industrial processes.
  • Syllabus and cross-curricular links:
  • Topic 3.2—periodic trends
  • Topic 21.1 and Option A.8—use of X-ray crystallography in structural determinations
  • Physics topic 5.1—electrostatics

Aims:

• Aim 3: Use naming conventions to name ionic compounds.
• Aim 6: Students could investigate compounds based on their bond type and properties or obtain sodium chloride by solar evaporation.
• Aim 7: Computer simulation could be used to observe crystal lattice structures.