Metals: Physical & Chemical Properties and Reactivity

Metals are the elements that conduct heat and electricity, shine when polished, and can be hammered into sheets or drawn into wires. About 80 of the 118 known elements are metals, from iron and copper to gold and aluminium. Their behaviour comes from a shared internal structure: a lattice of positive ions swimming in a sea of free-moving electrons.

Metals matter because modern civilisation is built on them — wires, buildings, vehicles, coins and surgical tools. Their chemical reactivity also decides how we extract them, why some corrode and others do not, and which ones are safe for cooking or implants. The reactivity series of metals is one of the most examined topics in school chemistry.

Key Concepts

• Malleability: can be hammered into thin sheets (gold into leaf); ductility: can be drawn into wires (copper into cables).
• Conductivity: free electrons carry electric current and heat quickly; silver is the best conductor, copper the practical choice.
• Lustre: the characteristic shine of a freshly cut metal surface; sonorous: metals ring when struck.
• Reactivity series: K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Ag > Au > Pt — a more reactive metal displaces a less reactive one from its compounds.
• Metal oxides: most are basic (Na2O, CaO turn red litmus blue); some like Al2O3 and ZnO are amphoteric, reacting with both acids and bases.
• Alloy: a homogeneous mixture of a metal with other elements, made to improve hardness or corrosion resistance — steel, brass, bronze.

How It Works

The sea-of-electrons model explains both physical and chemical behaviour:

1. Why they conduct: delocalised electrons flow freely through the lattice, carrying charge and thermal energy.
2. Why they bend: layers of positive ions can slide over each other without shattering, because the electron sea re-bonds instantly — hence malleability and ductility.
3. Reaction with oxygen: most metals burn or tarnish to form oxides; reactivity decides the violence (sodium bursts into flame, gold does nothing).
4. Reaction with water: K, Na and Ca react even with cold water; Mg reacts with steam; Fe and Zn react only with steam slowly; Cu, Ag and Au do not react at all.
5. Reaction with acids: metals above hydrogen in the series displace hydrogen gas from dilute acids; metals below hydrogen (Cu, Ag, Au) cannot.

Worked Example

Compare the volumes occupied by 100 g of aluminium and 100 g of iron, using densities of 2.70 g/cm³ for aluminium and 7.87 g/cm³ for iron.

1. Volume = mass ÷ density.
2. Aluminium: 100 ÷ 2.70 = 37.0 cm³.
3. Iron: 100 ÷ 7.87 = 12.7 cm³.
4. The same mass of aluminium takes up nearly three times the volume — which is why aluminium feels light and is chosen for aircraft bodies.
5. Note both are far denser than water (1 g/cm³), so both sink — a typical metallic trait, though a few metals like sodium (0.97 g/cm³) float.

Common Misconceptions

• "All metals are hard solids." Mercury is a liquid at room temperature, and sodium is soft enough to cut with a knife. Gallium even melts in your hand at about 30°C.
• "All metals react with acids to give hydrogen." Only metals above hydrogen in the reactivity series do. Copper, silver and gold sit below hydrogen and simply do not react with dilute hydrochloric or sulphuric acid.
• "Rusting happens to every metal." Rust specifically means hydrated iron(III) oxide on iron. Other metals corrode differently — aluminium forms a protective oxide skin, copper develops a green patina, silver tarnishes black.

Real-World Applications

• Electrical wiring: copper's ductility and conductivity make it the standard for household wiring worldwide.
• Aircraft and vehicles: aluminium alloys give strength at low weight, cutting fuel use.
• Coins and jewellery: copper, nickel, silver and gold resist corrosion, keeping coins and ornaments bright for decades.
• Construction: steel (iron + carbon) frames skyscrapers and bridges because of its unmatched strength per cost.

Metals conduct, shine, bend and ring because of their sea of free electrons, and they react according to the reactivity series — with oxygen, water and acids in predictable ways. Learn the series order cold, remember the exceptions like mercury and sodium, and both the physical and chemical questions about metals become straightforward.