Colourful Solutions > Models of bonding and structure > The ionic model

Introduction

Ionic bonding takes place between metal and non-metal atoms. The basic process involves several steps:

Syllabus reference S2.1.1
Syllabus reference S2.1.2
Syllabus reference S2.1.3

Structure 2.1.1 - When metal atoms lose electrons, they form positive ions called cations. When non-metal atoms gain electrons, they form negative ions called anions.

  • Predict the charge of an ion from the electron configuration of the atom.

Guidance

  • The formation of ions with different charges from a transition element should be included.

Tools and links

  • Structure 3.1 - How does the position of an element in the periodic table relate to the charge of its ion(s)?
  • AHL Structure 1.3 - How does the trend in successive ionization energies of transition elements explain their variable oxidation states?

Structure 2.1.2 - The ionic bond is formed by electrostatic attractions between oppositely charged ions.

  • Deduce the formula and name of an ionic compound from its component ions, including polyatomic ions.
  • Binary ionic compounds are named with the cation first, followed by the anion. The anion adopts the suffix “ide”.
  • Interconvert names and formulas of binary ionic compounds.

Guidance

  • The following polyatomic ions should be known by name and formula: ammonium NH4+, hydroxide OH–, nitrate NO3–, hydrogencarbonate HCO3–, carbonate CO32–, sulfate SO42–, phosphate PO43–.

Tools and links

  • Reactivity 3.2 - Why is the formation of an ionic compound from its elements a redox reaction?
  • AHL Structure 2.2 - How is formal charge used to predict the preferred structure of sulfate?
  • AHL Reactivity 3.1 - Polyatomic anions are conjugate bases of common acids. What is the relationship between their stability and the conjugate acid’s dissociation constant, Ka?

Structure 2.1.3 - Ionic compounds exist as three-dimensional lattice structures, represented by empirical formulas.

  • Explain the physical properties of ionic compounds to include volatility, electrical conductivity and solubility.

Guidance

  • Include lattice enthalpy as a measure of the strength of the ionic bond in different compounds, influenced by ion radius and charge.

Tools and links

  • Tool 1, Inquiry 2 - What experimental data demonstrate the physical properties of ionic compounds?
  • Structure 3.1 - How can lattice enthalpies and the bonding continuum explain the trend in melting points of metal chlorides across period 3?