Classify Metals & Non-Metals

The periodic table is split into two big regions by a zig-zag 'staircase' line that steps down the right-hand side (it runs roughly through boron, silicon, arsenic and tellurium).

• Metals take up the LEFT and CENTRE of the table — Groups 1 and 2, the transition metals in the middle, and most of the bottom-left of Groups 3–4. Most elements are metals.
• Non-metals are crowded into the TOP RIGHT — most of Groups 4–7 above the staircase, plus the Group 0 noble gases.
• The staircase line is the boundary: metals to the left of it, non-metals to the right.

Two special cases to remember.

• Hydrogen is usually drawn above Group 1, but it behaves like a non-metal — it is a colourless gas. Treat it as a non-metal.
• Metalloids (semi-metals) — elements that hug the staircase line, such as silicon (Si), boron (B) and germanium (Ge) — have properties in between metals and non-metals (e.g. silicon is shiny but a poor conductor; it is a semiconductor, the basis of computer chips).

Once you know whether an element is a metal or non-metal, you can predict its physical properties — and examiners love to test this both ways round (give properties → name the type, or give the type → list the properties).

Property	Metals	Non-metals
Appearance	shiny (lustrous)	dull
Conduct electricity?	yes (good)	no (poor) — graphite is the exception
Conduct heat?	yes (good)	no (poor)
Malleable / ductile?	yes — bend into shape, drawn into wires	no — brittle, shatter if solid
Sound when struck	sonorous (ring like a bell)	dull thud
Melting / boiling point	usually high	usually low
Density	usually high	usually low
State at room temperature	nearly all solid (mercury is liquid)	many are gases; some solid; bromine is liquid

Useful exceptions to memorise (examiners reward these):

• Mercury is the only metal that is liquid at room temperature.
• Graphite (a form of carbon, a non-metal) does conduct electricity — the one non-metal that does.
• Group 1 metals are unusually soft and have low density (lithium, sodium and potassium float on water) — but they are still metals chemically.
• Diamond (also carbon) is very hard and has a very high melting point, yet is still a non-metal.

These exceptions are exactly why you should never classify an element from one property alone — look at the overall pattern, and best of all, look at its position in the table.

The deepest difference between metals and non-metals is how they behave in reactions — and this is where the higher marks are.

1. Forming ions.

• Metals LOSE electrons to form POSITIVE ions (cations). They have few outer-shell electrons, so it is easiest to lose them. e.g. Na → Na⁺ + e⁻; Mg → Mg²⁺ + 2e⁻.
• Non-metals GAIN electrons to form NEGATIVE ions (anions). They have nearly-full outer shells, so it is easiest to gain a few. e.g. Cl + e⁻ → Cl⁻; O + 2e⁻ → O²⁻.

So, just from the type, you can predict the sign of the ion charge: metal → +, non-metal → −.

2. Forming oxides (and their acidity).

When elements react with oxygen they form oxides, and the type of oxide depends on the type of element:

• Metal oxides are BASIC (and the soluble ones are alkaline). e.g. Na₂O, MgO, CaO. They react with acids to form a salt and water; soluble ones turn damp litmus/universal indicator blue/purple (pH > 7).
• Non-metal oxides are ACIDIC. e.g. CO₂, SO₂, SO₃, NO₂. They dissolve in water to form acids (CO₂ → carbonic acid; SO₂/SO₃ → sulfurous/sulfuric acid) and turn indicator red/orange (pH < 7). They react with alkalis.

	Metal oxide	Non-metal oxide
Example	Na₂O, MgO, CaO	CO₂, SO₂, NO₂
Acid–base nature	basic / alkaline	acidic
Effect on indicator (if soluble)	blue/purple (pH > 7)	red/orange (pH < 7)
Reacts with…	acids	alkalis

Quick predictor: metal → positive ion → basic oxide; non-metal → negative ion → acidic oxide. Learn that chain and you can answer most spec-1.87 questions in one move.

Spec point 1.87 is all about prediction: given only where an element sits, you should be able to say whether it is a metal or non-metal and describe how it will behave.

The method:

1. Locate the element relative to the staircase line.
2. Left/centre → metal. Right of the staircase → non-metal. (On the line itself → metalloid, with in-between behaviour.)
3. Read off the likely properties from the type:
   • Metal → shiny, conducts heat/electricity, malleable/ductile, high m.p., loses e⁻ → positive ion → basic oxide.
   • Non-metal → dull, poor conductor, brittle/gas, low m.p., gains e⁻ → negative ion → acidic oxide.

Worked logic — element 'E' in Group 2, Period 4.

• Group 2 is on the far left → it is a metal.
• So predict: shiny, good conductor, high m.p./density, forms a 2+ ion (loses 2 outer electrons), forms a basic oxide.

Worked logic — element 'Q' in Group 6, Period 3 (sulfur).

• Group 6 is on the right, above the staircase → non-metal.
• So predict: dull, poor conductor, brittle solid (or a gas), low m.p., forms a 2− ion (gains 2 electrons), forms an acidic oxide (SO₂/SO₃).

This is a high-value skill: a single 'state whether X is a metal or non-metal and give a reason' is worth easy marks, and 'predict two properties' questions follow directly from the type.