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Ionic bonds form when electrons transfer from metal atoms to non-metal atoms, so Group 2 ions are +2 and Group 6 ions -2. Free notes and 9 questions answered.
How ionic bonds form through electron transfer is part of Chemical bonds, ionic, covalent and metallic in GCSE AQA Higher Chemistry.
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Ionic bonds form when electrons transfer from metal atoms to non-metal atoms, so Group 2 ions are +2 and Group 6 ions -2. Free notes and 9 questions answered.
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Use this lesson to stay inside Chemical bonds, ionic, covalent and metallic while connecting the detail back to the wider Topic 2: Bonding, structure, and the properties of matter topic.
Read the core explanations from How ionic bonds form through electron transfer before testing yourself from memory.
Picture sodium metal reacting with chlorine gas - there's a flash of light and suddenly you have table salt. What just happened at the atomic level? The answer lies in electron transfer, and it's all about atoms trying to become more stable.
Atoms are most stable when their outer shell is full of electrons, just like the noble gases in Group 0. But most atoms don't start with full outer shells. Metal atoms have just a few electrons in their outer shell, whilst non-metal atoms are nearly full but missing a few electrons.
Here's the key insight: it's easier for a sodium atom to lose its one outer electron than to gain seven more. Similarly, it's easier for chlorine to gain one electron than to lose seven. This is why electron transfer happens from metals to non-metals, never the other way round.
When sodium meets chlorine, something remarkable happens. The sodium atom has 11 electrons arranged as 2,8,1. That single electron in the outer shell is easily lost. The chlorine atom has 17 electrons arranged as 2,8,7 - just one electron short of a full outer shell.
Worked example: Sodium and Chlorine Electron Transfer
Show how sodium and chlorine atoms form ions through electron transfer
Answer: Na⁺ and Cl⁻ ions are formed, both with stable noble gas electron arrangements
Here's where the periodic table becomes your best friend. The group number tells you exactly how many electrons an atom has in its outer shell. This makes predicting ionic charges straightforward once you know the pattern.
Group 1 metals have 1 outer electron, so they lose 1 electron to form +1 ions. Group 2 metals have 2 outer electrons, so they lose 2 electrons to form +2 ions. Group 6 non-metals have 6 outer electrons, so they gain 2 electrons to form -2 ions. Group 7 non-metals have 7 outer electrons, so they gain 1 electron to form -1 ions.
Worked example: Predicting Ion Charges
Predict the charges on ions formed by: lithium (Group 1), magnesium (Group 2), oxygen (Group 6), and fluorine (Group 7)
Answer: Li⁺, Mg²⁺, O²⁻, F⁻ - all with noble gas structures
You might wonder why atoms 'want' to have noble gas structures. The answer is stability. Noble gases are incredibly unreactive because their electron arrangements are so stable. When other atoms achieve the same electron arrangement, they become much more stable too.
This explains why ionic compounds are so stable. The sodium ion Na⁺ has the same electron arrangement as neon (2,8). The chloride ion Cl⁻ has the same electron arrangement as argon (2,8,8). Both are much more stable than the original atoms.
Exam questions on ionic bonding often test whether you can predict charges correctly and explain the electron transfer process. The key is being systematic and showing your working clearly.
The biggest mistake students make is confusing ionic and covalent bonding. Remember: ionic bonding involves complete electron transfer between metals and non-metals. Covalent bonding involves electron sharing between non-metals only.
Master this topic and you'll find the rest of ionic bonding much easier. The key insight is that electron transfer creates stable ions with noble gas structures, and these oppositely charged ions attract each other strongly.
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Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.
Metal atoms have just a few outer electrons, while non-metal atoms are nearly full. It is easier for a sodium atom to lose its one outer electron than to gain seven, and easier for chlorine to gain one electron than to lose seven, so electrons transfer from metals to non-metals.
Group 2 ions have a charge of +2, because Group 2 metals have 2 outer electrons and lose both. For example, magnesium forms Mg²⁺, which has the electron arrangement 2,8, like neon.
Group 6 ions have a charge of -2, because Group 6 non-metals have 6 outer electrons and gain 2 more to fill their outer shell. For example, oxygen forms O²⁻, with the electron arrangement 2,8, like neon.
Electron transfer is the movement of electrons from metal atoms to non-metal atoms during chemical bonding. It creates oppositely charged ions that attract each other, forming an ionic bond.
The group number gives the number of outer electrons. Group 1 metals lose 1 electron to form +1 ions and Group 2 metals lose 2 to form +2 ions, while Group 6 non-metals gain 2 electrons to form -2 ions and Group 7 non-metals gain 1 to form -1 ions.
Ions form with noble gas structures because a full outer shell is very stable, like the unreactive Group 0 elements. Na⁺ has the same arrangement as neon (2,8) and Cl⁻ the same as argon (2,8,8), so the ions are much more stable than the original atoms.
Lithium (Group 1) forms Li⁺, magnesium (Group 2) forms Mg²⁺, oxygen (Group 6) forms O²⁻ and fluorine (Group 7) forms F⁻. Li⁺ has the arrangement 2, like helium, while Mg²⁺, O²⁻ and F⁻ are all 2,8, like neon.
A sodium ion has a positive charge because it has more protons than electrons: Na → Na⁺ + e⁻, so Na⁺ has 11 protons and 10 electrons. A chloride ion is negative because it has gained an electron, with 17 protons and 18 electrons.
Sodium loses one electron instead of gaining seven because it is much easier to lose a single outer electron than to gain seven more. Similarly, chlorine gains one electron rather than losing seven, so electron transfer goes from metals to non-metals.