Let's walk through sodium chloride (NaCl) — table salt:
• Electron configuration: 2,8,1
• Has 1 electron in outer shell
• Loses this electron to achieve a stable 2,8 configuration (like neon)
• 11 protons, 11 electrons → neutral
• Electron configuration: 2,8,7
• Has 7 electrons in outer shell — one electron short of a stable configuration
• Gains 1 electron to achieve a stable 2,8,8 configuration (like argon)
• 17 protons, 17 electrons → neutral
• Sodium's outer electron jumps to chlorine
• This is a chemical reaction — atoms change!
• Neither atom is neutral anymore
• Sodium: 11 protons, 10 electrons → Na⁺ (positive ion = CATION)
• Chlorine: 17 protons, 18 electrons → Cl⁻ (negative ion = ANION)
• Both now have full outer shells!
• Na⁺ and Cl⁻ are oppositely charged
• Opposite charges attract (electrostatic attraction)
• This attraction IS the ionic bond
• Very strong — takes lots of energy to break!
Why do Group 1 metals form +1 ions? They have 1 outer electron to lose.
Why do Group 2 metals form +2 ions? They have 2 outer electrons to lose.
Why do Group 7 elements form -1 ions? They are 1 electron short of a stable full outer shell.
Why do Group 6 elements form -2 ions? They are 2 electrons short of a stable full outer shell.
The Charge Rule: The charge on an ion = number of electrons lost or gained. Metals lose electrons (positive charge), non-metals gain electrons (negative charge). The number equals how far they are from a full shell!
This deep dive covers Understanding Ionic Bonding Step by Step within Ionic Bonding for GCSE Chemistry. Revise Ionic Bonding in Bonding & Structure for GCSE Chemistry with 35 exam-style questions and 20 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 3 of 16 in this topic. Use this deep dive to connect the idea to the wider topic before moving on to questions and flashcards.
Practice questions for Ionic Bonding
Which combination of elements forms an ionic compound?
Describe the structure of an ionic compound and explain why ionic compounds have high melting points. [3 marks]