You are viewing a free preview of this lesson.
Subscribe to unlock all 10 lessons in this course and every other course on LearningBro.
This lesson covers ionic bonding — the transfer of electrons between metals and non-metals to form charged particles called ions — as required by the Edexcel GCSE Combined Science specification (1SC0). You need to understand how ionic bonds form, draw dot-and-cross diagrams, and explain why ions have charges.
Ionic bonding is the electrostatic attraction between oppositely charged ions. It occurs between a metal and a non-metal.
The process involves the transfer of electrons:
Exam Tip: Always state that ionic bonding involves the transfer of electrons, not the sharing of electrons. Sharing is covalent bonding.
Atoms are most stable when they have a full outer electron shell. This is the same electron configuration as a noble gas (Group 0). Atoms achieve this by:
| Atom | Group | Electrons Lost/Gained | Ion Formed | Noble Gas Configuration |
|---|---|---|---|---|
| Sodium (Na) | 1 | Loses 1 electron | Na⁺ | Neon (2, 8) |
| Magnesium (Mg) | 2 | Loses 2 electrons | Mg²⁺ | Neon (2, 8) |
| Aluminium (Al) | 3 | Loses 3 electrons | Al³⁺ | Neon (2, 8) |
| Chlorine (Cl) | 7 | Gains 1 electron | Cl⁻ | Argon (2, 8, 8) |
| Oxygen (O) | 6 | Gains 2 electrons | O²⁻ | Neon (2, 8) |
Exam Tip: The charge on an ion can be predicted from the group number. Group 1 metals form +1 ions, Group 2 form +2 ions, Group 6 non-metals form −2 ions, and Group 7 non-metals form −1 ions.
A dot-and-cross diagram shows how electrons are transferred during ionic bonding. Dots represent electrons from one atom and crosses represent electrons from the other.
graph LR
A["Na atom<br/>2, 8, 1"] -->|"Loses 1 electron"| B["Na⁺ ion<br/>2, 8"]
C["Cl atom<br/>2, 8, 7"] -->|"Gains 1 electron"| D["Cl⁻ ion<br/>2, 8, 8"]
A -->|"1 electron transferred"| C
style A fill:#2980b9,color:#fff
style B fill:#27ae60,color:#fff
style C fill:#e67e22,color:#fff
style D fill:#27ae60,color:#fff
When drawing dot-and-cross diagrams for ionic compounds in the exam:
Exam Tip: Always include square brackets and charges on your dot-and-cross diagrams. Missing brackets or charges will lose marks even if the electron arrangement is correct.
To work out the formula, make sure the total positive charge equals the total negative charge so the compound is neutral overall.
| Positive Ion | Negative Ion | Balancing | Formula |
|---|---|---|---|
| Na⁺ | Cl⁻ | 1 × (+1) + 1 × (−1) = 0 | NaCl |
| Mg²⁺ | Cl⁻ | 1 × (+2) + 2 × (−1) = 0 | MgCl₂ |
| Na⁺ | O²⁻ | 2 × (+1) + 1 × (−2) = 0 | Na₂O |
| Ca²⁺ | F⁻ | 1 × (+2) + 2 × (−1) = 0 | CaF₂ |
| Al³⁺ | O²⁻ | 2 × (+3) + 3 × (−2) = 0 | Al₂O₃ |