Metals & Non-Metals

Most elements are metals, a smaller set are non-metals, and a handful sit on the dividing line showing properties of both.

• Non-metals are dull, brittle and poor conductors, such as carbon, sulphur, oxygen and nitrogen.
• Metalloids show properties of both metals and non-metals, for example silicon, germanium, arsenic and boron.
• About 78% of all known elements are metals, so metals far outnumber non-metals in the periodic table.
• In the periodic table, metals lie on the left and centre, non-metals on the upper right, with metalloids along the staircase line between them.

Metals share a distinctive set of physical properties that come from their tightly packed atoms and free-moving electrons.

• Malleable — metals can be beaten into thin sheets; gold and silver are the most malleable metals.
• Ductile — metals can be drawn into thin wires; gold is the most ductile metal.
• Metals are good conductors of heat and electricity; silver is the best conductor, followed by copper.
• Sonorous — metals produce a ringing sound when struck, which is why bells are made of metal.
• Metals generally have high density and high melting points, e.g. tungsten has the highest melting point of any metal.
• Metals are solids at room temperature, except mercury, which is the only metal that is liquid.

Non-metals are, in almost every respect, the opposite of metals in their physical character.

• Non-metals are brittle and break easily; they are neither malleable nor ductile.
• Non-metals are poor conductors of heat and electricity, the great exception being graphite, which conducts electricity.
• Non-metals generally have low melting and boiling points and low density.
• Non-metals are not sonorous — they do not ring when struck.
• Non-metals exist as solids, liquids and gases; bromine is the only non-metal that is liquid at room temperature.

A direct comparison brings out how each physical property of a metal is mirrored by the opposite property in a non-metal.

The chemistry of metals and non-metals differs most clearly in the nature of the oxides they form.

• Basic metal oxides turn red litmus blue and react with acids to form salt and water.
• Non-metals react with oxygen to form acidic oxides, e.g. carbon dioxide (CO₂) and sulphur dioxide (SO₂).
• Acidic non-metal oxides turn blue litmus red and react with bases to form salt and water.
• Some metal oxides are amphoteric, reacting with both acids and bases — for example aluminium oxide (Al₂O₃) and zinc oxide (ZnO).

At the atomic level, metals and non-metals behave oppositely when they form chemical bonds.

• Non-metals gain electrons to form negative ions (anions), e.g. Cl + e⁻ → Cl⁻; non-metals are therefore electronegative.
• Metals are reducing agents because they donate electrons.
• Non-metals are oxidising agents because they accept electrons.

• Metals react with dilute acids to release hydrogen gas, e.g. Zn + H₂SO₄ → ZnSO₄ + H₂↑.
• Non-metals generally do not react with dilute acids to displace hydrogen.

Metals can be arranged in order of how readily they react — their reactivity — and this single list explains a great deal of metal chemistry.

• The standard order is:

K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au > Pt.

• Potassium (K) and sodium (Na) are the most reactive metals, sitting at the very top.
• Gold (Au) and platinum (Pt) are the least reactive (noble) metals, sitting at the bottom.
• Hydrogen (H) is placed in the series as a reference; metals above it can displace hydrogen from dilute acids, while metals below it cannot.

The reactivity series directly predicts which metal can push another out of its compound.

• Example: Fe + CuSO₄ → FeSO₄ + Cu — iron (more reactive) displaces copper, and the blue colour of copper sulphate fades.
• Example: Zn + CuSO₄ → ZnSO₄ + Cu — zinc displaces copper from copper sulphate.
• A less reactive metal cannot displace a more reactive one, so copper cannot displace iron from FeSO₄.
• Metals above hydrogen displace hydrogen gas from dilute acids, while gold, silver and copper (below H) do not.

A pure metal is often too soft or too easily corroded, so it is mixed with other elements to improve its properties.

• Alloying is done to increase strength, hardness, or resistance to corrosion, or to lower cost.
• Steel is an alloy of iron and carbon — adding carbon makes soft iron hard and strong.
• An amalgam is any alloy in which one of the metals is mercury.

Each well-known alloy has a fixed combination of metals chosen for a specific job, and these are heavily tested.

• Bell metal = Copper + Tin (a bronze with more tin), used to cast bells.
• Gun metal = Copper + Tin + Zinc, used for gears, bearings and castings.
• Magnalium = Aluminium + Magnesium, light and used in aircraft parts.

Metals exposed to air and moisture slowly deteriorate, and preventing this is a major use of alloying and coatings.

• Rusting of iron forms hydrated iron(III) oxide (Fe₂O₃·xH₂O), a reddish-brown layer, and needs both air (oxygen) and water.
• Silver tarnishes (black) and copper forms a green coating over time.

• Galvanisation is coating iron with a layer of zinc to protect it from rusting.
• Painting, greasing, oiling, and electroplating also prevent corrosion by keeping out air and moisture.
• Making stainless steel (with chromium and nickel) makes iron rust-resistant.

Most metals occur in nature combined with other elements, and extracting them from the earth is the science of metallurgy.

• An ore is a mineral from which a metal can be extracted profitably (economically).
• All ores are minerals, but not all minerals are ores.
• Metallurgy is the overall process of extracting a metal from its ore and refining it for use.
• Gangue is the unwanted earthy impurity present in an ore.

Getting a pure metal from its ore follows a general sequence, with the key step depending on whether the ore is a sulphide or a carbonate.

• Roasting heats a sulphide ore strongly in the presence of air to convert it to an oxide, e.g. 2ZnS + 3O₂ → 2ZnO + 2SO₂.
• Calcination heats a carbonate ore strongly in the absence (or limited supply) of air to convert it to an oxide, e.g. ZnCO₃ → ZnO + CO₂.
• Reduction converts the metal oxide to the free metal, often by heating with carbon (e.g. ZnO + C → Zn + CO).
• Refining purifies the extracted metal, commonly by electrolysis.

A number of elements break the usual metal/non-metal rules, and these exceptions are among the most frequently asked facts.

• Bromine is the only non-metal that is liquid at room temperature.
• Gallium and caesium are metals that melt just above room temperature, e.g. gallium melts at about 30°C and can melt in the palm of the hand.
• Graphite is the only non-metal that conducts electricity well (used in electrodes), because of its free electrons.
• Diamond is the hardest natural substance**, yet it is a non-metal (a form of carbon) and does not conduct electricity.
• Graphite is one of the softest substances while diamond is the hardest — both are allotropes of carbon.
• Iodine is a non-metal that has a metallic lustre, an exception to the "non-metals are dull" rule.
• Hydrogen is a non-metal placed at the top of the periodic table but behaves like the alkali metals in some reactions.