Lesson focus: Metals and non-metals often react by electron transfer, forming ionAn atom (or group of atoms) that has an electric charge because it has gained or lost electrons. whose charges determine the formula of the product.
Use outer-electron patterns and ion charges to explain metal–non-metal reactions and construct simple ionic formulae.
Build on earlier learning
The elements of Group 7Group 7 atoms were described as gaining electrons. This lesson links that pattern to metals losing electrons and forming ionic compounds.
You will be successful when you can…
- Distinguish metal and non-metal ion formation.
- Explain ionic attraction.
- Construct neutral formulae from ion charges.
- Avoid treating ionic compounds as molecules.
Words that carry the science
- ion
- A charged particle formed when an atom or group gains or loses electrons.
- cation
- A positively charged ion.
- anion
- A negatively charged ion.
- ionic bond
- The electrostatic attraction between oppositely charged ions.
- formula unit
- The simplest whole-number ratio of ions in an ionic compound.
- oxidation
- Loss of electrons; at this level it can also describe reaction with oxygen in a narrower context.
Track electron transfer and conserve overall charge
01Metals lose electrons and non-metals gain them
Group 1 metals form 1+ ions, Group 2 metals form 2+ ions, and Group 7 non-metals form 1− ions in simple models. Sodium transfers one electron to chlorine, producing Na⁺ and Cl⁻.
Electron transfer changes electron arrangements but does not change the number of protons in each nucleus, so the elements retain their identities.
02Opposite charges attract in a giant lattice
Positive and negative ions attract in all directions, forming a giant ionic latticeA huge, regular 3D arrangement of positive and negative ions held together by strong electrostatic attraction, as in sodium chloride.. Sodium chloride is written NaCl because its ions combine in a 1:1 ratio, not because separate NaCl molecules normally exist in the solid.
Magnesium chloride needs two chloride ions for each magnesium ion: Mg²⁺ + 2Cl⁻ gives MgCl₂. The formula is chosen so total positive and negative charge is zero.
03Reactions can be energetic and hazardous
Metal–non-metal reactions can release substantial energy. Burning magnesium gives intense white light and hot magnesium oxide; reactive metals with halogens require specialist demonstrations or simulations.
Observations support that a reaction occurred, but flame colour alone does not reveal the complete bonding model. Particle models are explanations tested against several properties and measurements.
Construct magnesium chloride
Write the formula formed from Mg²⁺ and Cl⁻.
- One magnesium ion contributes +2 charge.
- Each chloride ion contributes −1 charge.
- Two chloride ions provide −2 in total.
- The neutral formula unitThe simplest group of ions in an ionic compound, such as one sodium ion and one chloride ion in NaCl. is MgCl₂.
How to make the reasoning visible: Use the smallest whole-number ratio that makes the total charge zero.
Balance ion charges
Use the stated common ion charges; do not alter the ions themselves.
| Cation | Anion | Charge balance | Formula | Name |
|---|---|---|---|---|
| Na⁺ | Cl⁻ | 1+ and 1− | NaCl | Sodium chloride |
| Mg²⁺ | O²⁻ | 2+ and 2− | MgO | Magnesium oxide |
| Mg²⁺ | Cl⁻ | 2+ and two 1− | MgCl₂ | Magnesium chloride |
| Al³⁺ | O²⁻ | two 3+ and three 2− | Al₂O₃ | Aluminium oxide |
Why is magnesium oxide MgO rather than Mg₂O₂?
Why is solid sodium chloride not described accurately as separate NaCl molecules?
Check your understanding
Answer from memory, then check against the suggested answer.
What charge does a Group 1 metal ion usually have?
What is an ionic bond?
Why is MgCl₂ neutral?
Predict the formula of aluminium chloride from Al³⁺ and Cl⁻.
Explain why electron transfer alone is not the complete definition of an ionic bond.
Exam Question Practice
Exam Question Practice
Mark points shown after marking
Magnesium reacts with chlorine to form magnesium chloride, MgCl₂.
Describe the electron transfer that forms the ions.
(3)Explain the bonding and the formula MgCl₂.
(2)Total for this question: 5 marks
Command word: For explainA command word: say how or why something happens, giving reasons with words like "because" or "so"., track electrons and charges explicitly, then connect the balanced ion ratio to the formula.