Ionic bonding — AQA GCSE Chemistry
Test yourself on Ionic bonding with AQA GCSE practice questions.
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Ionic bonding explained
Non-metal atoms have outer shells that are closer to full, so gaining electrons is energetically favourable and produces a negative ion.
Read the full explanation
For example, a chlorine atom has the electronic structure 2,8,7; gaining one electron gives Cl⁻ with the structure 2,8,8, the same as argon. The number of electrons gained is usually 8 minus the group number for Groups 6 and 7, so oxygen (2,6) gains two electrons to form O²⁻ and chlorine gains one to form Cl⁻. The charge is written as a superscript after the symbol, and the size of the negative charge equals the number of electrons gained. This electron gain is the second half of ionic bonding and explains the anions in compounds such as NaCl and MgO.
Your focus
- State that non-metal atoms gain electrons to form negative ions.
- Deduce the charge on a non-metal ion from its group number.
- Write the symbol and charge of a non-metal ion correctly using superscript notation.
Ionic bonding exam tips
Marking Points
- Non-metal atoms gain electrons into their outermost shell until that shell is full.
- The number of electrons gained is 8 minus the group number for Groups 6 and 7.
- Gain of electrons produces a negative ion because the number of electrons now exceeds the number of protons.
- The charge on the ion is written as a superscript, for example O²⁻, F⁻ and Cl⁻.
- The electronic structure of the ion formed is that of the nearest noble gas, for example Cl⁻ is 2,8,8 like argon.
Examiner Tips
- 💡Count the electrons needed to complete the outer shell before writing the ion.
- 💡Use the group number to work out the charge quickly: Group 7 forms 1⁻ ions and Group 6 forms 2⁻ ions.
- 💡Check that the superscript charge is negative and matches the number of electrons gained.
Common Mistakes
- Writing the charge on the baseline, such as Cl1⁻, instead of using a superscript: the correct form is Cl⁻.
- Saying that non-metal atoms lose electrons to become negative ions: non-metals gain electrons, and losing electrons would make the ion positive.
- Miscounting the electrons gained, for example giving oxygen a single negative charge when it gains two electrons to form O²⁻.