What are inorganic substances?
An element is a substance made of only one kind of atom. Inorganic chemistry studies all elements and the compounds they form, such as salts, oxides, acids and metals. It leaves out most carbon-chain compounds, which are called organic.
To find our way, chemists use the periodic table. It puts elements in columns called groups, and rows called periods. Elements in a group have the same number of outer electrons, so they behave in a similar way.
Main-group elements
Main-group (or representative) elements are in groups 1, 2 and 13 to 18. Their outer electrons fill the s or p shell.
- Group 1, alkali metals (Li, Na, K): soft, light, very reactive. They react with water and give a +1 ion.
- Group 2 (Mg, Ca): harder, less reactive, give a +2 ion.
- Groups 13 to 16: a mix of metals (Al), half-metals (Si) and non-metals (C, N, O, S).
- Group 17, halogens (F, Cl, Br, I): reactive non-metals. They gain one electron and make salts with metals.
- Group 18, noble gases (He, Ne, Ar): full outer shell, so they hardly react.
Going down a group, metals get more reactive; non-metals get less reactive.
Transition elements
Transition elements are in groups 3 to 12, from scandium to zinc in period 4. They fill the d shell, so they are called d-block elements.
- Hard, dense metals with high melting points (Fe, Cu, Ni).
- Conduct heat and electricity well.
- Form coloured ions: Cu²⁺ is blue, Fe²⁺ green, Fe³⁺ yellow-brown, MnO₄⁻ purple.
- Show more than one charge: iron is Fe²⁺ or Fe³⁺.
- Work as catalysts: iron in making ammonia, vanadium oxide in making sulphuric acid.
Zinc is placed in the block but has a full d shell. Its ion is colourless and has only one charge, so it is a special case.
Main group against transition: side by side
| Property | Main group (s and p blocks) | Transition (d block) |
|---|---|---|
| Hardness | Group 1 is soft | Hard |
| Charges | Usually one fixed charge | Often several |
| Ion colour | Mostly colourless | Often coloured |
| Catalyst | Rare | Common |
Try it
Open the 3D. At step 4 change nothing, just look at the tubes. Then ask: "Which tube would be colourless if it held a group 1 ion like Na⁺?" Predict first, then press the Group 1 button and read the facts. At home, look at a blue copper-sulphate crystal or a rusty iron nail and say which block each element belongs to.
Key formulas and definitions
- Group 1 ion: M⁺; Group 2 ion: M²⁺; Group 17 ion: X⁻
- Main group: groups 1, 2, 13–18; Transition: groups 3–12
- Iron ions: Fe²⁺ (green), Fe³⁺ (yellow-brown)
Worked examples
1. Is sodium (Na) a main-group or a transition element? Which group?
Sodium is in group 1, an alkali metal, so it is a main-group element.
2. Copper sulphate solution is blue. Which type of element makes a coloured ion like this?
Copper is a transition element. Transition ions often have partly filled d shells and are coloured.
3. Why does neon not make compounds easily?
Neon is in group 18. Its outer shell is full, so it does not need to gain or lose electrons.
Common mistakes
- Thinking every element in the middle of the table is a transition element. Check the group numbers 3 to 12.
- Saying all main-group elements are non-metals. Groups 1 and 2 are all metals.
- Forgetting that iron can be Fe²⁺ or Fe³⁺. Transition metals can have more than one charge.
- Believing noble gases never react. They hardly react, but a few compounds exist.