The periodic table · Contrast
Metals and non-metals
Two grey solids, both dull, both heavy, and both of them conduct electricity. One is a metal and one is not — so which single test tells them apart?
Start here
Two grey solids on the bench. One is lead. One is a lump of graphite from a pencil.
Both are dull grey. Both are heavy for their size. Both mark paper if you press hard enough, and — the awkward part — both conduct electricity when you wire them into a circuit with a bulb.
Which single test would separate them?
Hit them. The lead flattens; the graphite shatters into black dust. Metals are malleable — they change shape without breaking, because their atoms can slide past each other and stay held together. Non-metal solids are brittle and crack. Conducting electricity was never going to settle it: graphite is the one non-metal that conducts, and it is the reason no single property can be trusted on its own.
About three-quarters of the elements are metals. They are shiny when freshly cut, conduct heat and electricity, bend rather than break, and nearly all of them are solid at room temperature with high melting points.
Non-metals are the opposite on every count: dull, poor conductors, brittle if solid at all, and many are gases. There are only about twenty of them — and they include the ones life is made of.
Reference · keep this one open
The two lists, side by side
- AppearanceShiny when freshly cut or polishedDull, or transparent, or invisible as a gas
- Hit with a hammerFlattens — malleableShatters — brittle
- ElectricityConducts, all of themInsulates, except graphite
- HeatConducts well — a metal spoon in tea gets hotInsulates — a wooden one does not
- Melting pointUsually high; iron melts at 1538 °CUsually low; most are gases at room temperature
- SoundRings when struck — sonorousThuds or cracks
Every row has an exception somewhere in the table. That is not a flaw in the list — it is the reason you judge an element on several properties rather than one.
Your turn · six unlabelled samples
Read the data. Metal or non-metal?
0 of 6 decided
Sample A
solid
- Silvery and shiny where it has been cut
- Bends around a former without cracking
- Conducts electricity; melts at 660 °C
Metal
Aluminium. A metal on every count — shiny, malleable, conducting, high melting point. Every property agrees, which is what an easy identification looks like.
Sample B
solid
- Dull grey and marks paper
- Shatters into flakes when hit
- Conducts electricity
Non-metal
Graphite — carbon, and a non-metal. The conducting is the exception; the brittleness and the dullness are the rule. Three properties against one settles it.
Sample C
liquid
- Silvery and mirror-bright
- Conducts electricity
- Freezes solid at −39 °C
Metal
Mercury — a metal, and the one that is liquid at room temperature. Its melting point breaks the pattern; everything else about it is metallic.
Sample D
solid
- Bright yellow and crumbly
- Does not conduct electricity
- Melts at 115 °C and burns with a blue flame
Non-metal
Sulfur, a non-metal. Dull, brittle, insulating and low-melting — non-metallic on every count and the easiest sample here.
Sample E
solid
- Cuts with a knife like hard cheese
- Floats on water and reacts with it violently
- Shiny on the freshly cut surface, then dulls in seconds
Metal
Sodium — a metal, and one you will meet again. Soft enough to cut and light enough to float, which is nothing like the metals in a toolbox. The shine on the cut surface is the giveaway.
Sample F
gas
- Colourless and has no smell
- Does not conduct electricity
- Boils at −196 °C
Non-metal
Nitrogen, a non-metal, and three-quarters of the air in the room. No element that is a gas at room temperature is a metal.
Three of those broke a rule and were still what they were.
Mercury is a metal that is liquid. Graphite is a non-metal that conducts. Sodium is a metal soft enough to cut with a knife and light enough to float. If you had judged any of them on one property you would have got them wrong — and if you had judged them on four, you would have got them right.
Key fact
Metals are shiny, malleable conductors with high melting points. Non-metals are dull, brittle insulators, and many are gases. Judge an element on the whole set, never on one property.
Six words
Say your answer out loud before you turn each card over. If you cannot say it, you do not know it yet.
Think again
“If it conducts electricity it must be a metal.”
Conducting is the property everyone reaches for first. Commit before you read on.
Graphite conducts electricity as well as some metals do, and it is carbon — one of the most thoroughly non-metallic elements there is. It is brittle, it has no shine worth the name, and it forms the acidic oxide that made your limewater go milky.
Which is why classification uses a set of properties and not a single test. One property is a clue. Four agreeing properties is an identification. The same logic runs through the whole of chemical analysis.
Mastery ladder
Not started yet.
Rungs 3 and 4 you mark yourself.
Rung 1 · Recall
Which set of properties describes a typical metal?
Rung 2 · The one that catches people
An unknown element is a liquid at room temperature. What can you conclude?
Rung 3 · Explain
A student is given an unknown solid element. Describe the tests you would carry out to decide whether it is a metal or a non-metal, and explain why one test alone would not be enough.
Rung 4 · Take it somewhere new
Saucepans are made of metal but the handles are usually plastic or wood. Explain the choice of each material in terms of the properties in this lesson, and say what would go wrong if the two were swapped.
Key note
Metals are shiny, malleable, sonorous, and good conductors of heat and electricity, with high melting and boiling points. Non-metals are dull, brittle when solid, poor conductors, and often gases. Exceptions exist for every single property — mercury, graphite, sodium — so elements are classified on the whole pattern rather than one test.
Going further
The dividing line on the periodic table runs as a staircase down the right-hand side, and the elements sitting on it refuse to choose. Silicon is shiny like a metal and brittle like a non-metal; it conducts, but only a bit, and only under some conditions. That halfway behaviour is the reason it is in every computer ever built — a semiconductor is useful precisely because it can be persuaded to conduct or not.
The properties are not a list to be memorised; they all follow from one thing. In a metal, the outer electrons are not tied to individual atoms — they move freely through the whole structure. Free electrons carry charge, which makes metals conduct; they carry energy, which makes metals conduct heat; and they let layers of atoms slide over each other and stay bonded, which makes metals bend instead of shatter. One idea, five properties.
Before this lesson
Next in this unit
At GCSE this becomes
- Metallic bonding and the sea of delocalised electrons, and how position in the table predicts whether an oxide is acidic or basic.
Where to next
- Next: Mendeleev and the table that predicted
- Previous: Measuring a temperature change
Energy changes in reactions
Ask Mr Badmus AI
Still unsure why graphite breaks the rule?
Sample E is sodium and is a teacher demonstration, behind a screen, with the smallest piece that can be cut. Mercury is not handled in a school laboratory at all — the sample on this bench is data, not a bottle on a shelf.
Lesson content © MrBadmusAI.