IGCSE Chemistry Inorganic Chemistry Notes
The periodic table organises elements by proton number. Elements in the same group have similar properties because they have the same number of outer electrons.
Key concepts
- Group
- A vertical column; all members have the same number of outer-shell electrons.
- Period
- A horizontal row; across a period, elements go from metals to non-metals.
- Group 1 (alkali metals)
- Soft, reactive metals that form 1+ ions; reactivity increases down the group.
- Group 7 (halogens)
- Reactive non-metals forming 1− ions and diatomic molecules; reactivity decreases down the group.
- Transition metals
- Hard, dense metals with high melting points, coloured compounds and variable oxidation states.
- Group 1 metals react vigorously with water to give hydrogen and an alkaline hydroxide.
- Halogen displacement: a more reactive halogen displaces a less reactive one from its salt.
- Noble gases (Group 0) are unreactive because they have full outer shells.
- Metals lose electrons in reactions; non-metals tend to gain them.
Worked example
Predict the products when lithium reacts with water and write a balanced equation.
- 1Group 1 metal + water → metal hydroxide + hydrogen
- 22Li + 2H₂O → 2LiOH + H₂
- 3Solution turns universal indicator purple (alkaline).
Answer: 2Li + 2H₂O → 2LiOH + H₂ (fizzing, floats, gives an alkaline solution)
Common mistakes
✗ Saying Group 1 metals get less reactive down the group.
✓ They get more reactive — outer electron is further from the nucleus and lost more easily.
✗ Confusing Group 7 trend with Group 1.
✓ For Group 7, reactivity decreases down the group (harder to gain an electron).
✗ Writing halogens as single atoms.
✓ Halogens exist as diatomic molecules: Cl₂, Br₂, I₂.
Quick check
Try these, then reveal the answers.
Why do all Group 1 elements have similar reactions?Reveal answer
They all have 1 electron in their outer shell.
Which is more reactive: chlorine or iodine?Reveal answer
Chlorine — reactivity decreases down Group 7.
Give one property that distinguishes transition metals from Group 1 metals.Reveal answer
Higher density / higher melting point / coloured compounds / variable oxidation states.
Exam tips
- For trends, always explain in terms of electron shells and nuclear attraction.
- Write halogens as X₂ molecules in equations.
- Learn one full observation (fizzing, floats, moves, disappears) for Group 1 + water.
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Frequently asked questions
Why is Group 0 unreactive?+
Noble gases already have full outer shells, so they do not need to gain or lose electrons.
What is a displacement reaction?+
A reaction where a more reactive element takes the place of a less reactive one in a compound.
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