Learning focus
Develop precise chemical language, connect particle and bonding models to observations, interpret diagrams and data, and apply ideas to unfamiliar examples.
Formation of ions
Ionic bonding usually occurs between a metal and non-metal. The metal loses outer electrons and the non-metal gains them. The resulting ions have opposite charges and often noble-gas electron configurations.
Definition of ionic bond
An ionic bond is a strong electrostatic attraction between oppositely charged ions. The bond is not the transferred electron; transfer creates ions, and attraction between the ions is the bonding force.
Sodium chloride
Sodium 2,8,1 loses one electron to form Na+ 2,8. Chlorine 2,8,7 gains the electron to form Cl- 2,8,8. A 1:1 ratio gives the neutral formula NaCl.
Magnesium chloride
Magnesium loses two electrons to form Mg2+. Two chlorine atoms each gain one electron to form two Cl-. Charge balance gives MgCl2.
Dot-and-cross diagrams
Use different symbols for electrons from different atoms. Put brackets and charges around ions and show complete outer shells. The diagram must conserve the total number of electrons transferred.
Practical or data skill
Construct dot-and-cross diagrams for NaCl, MgO, MgCl2 and CaF2. Check the total charge is zero.
Examination tip
Describe electron transfer first, then define the electrostatic attraction.
Review questions and suggested answers
Question 1
Define an ionic bond.
Suggested answer
Strong electrostatic attraction between oppositely charged ions.
Question 2
Why is MgCl2 the formula?
Suggested answer
One Mg2+ balances two Cl- ions.
Question 3
Which type of element forms a cation?
Suggested answer
Usually a metal.
