Metals and Non-metals

1. Physical Properties of Metals and Non-metals

Metals

Most metals are lustrous, hard, malleable, ductile, sonorous and good conductors of heat and electricity. They generally have high melting and boiling points.

Non-metals

Non-metals are generally brittle in the solid state, non-lustrous and poor conductors. They are not malleable or ductile and are usually non-sonorous.

2. Chemical Properties of Metals and Non-metals

2.1 Reaction with oxygen

Metals generally react with oxygen to form metal oxides.

Metal oxides are generally basic, although some are amphoteric. Aluminium oxide and zinc oxide react with both acids and bases.

Non-metals generally form acidic or neutral oxides.

2.2 Reaction with water

Different metals react with water with different intensities.

2.3 Reaction with acids

Metals above hydrogen in the reactivity series generally react with dilute acids to form salt and hydrogen.

Metals below hydrogen, such as copper, generally do not liberate hydrogen from dilute non-oxidising acids.

2.4 Reaction with bases

Some metals react with strong bases. Zinc reacts with sodium hydroxide to form sodium zincate and hydrogen.

2.5 Displacement reactions

A more reactive metal displaces a less reactive metal from its salt solution.

Copper cannot displace zinc from zinc sulphate because copper is less reactive than zinc.

2.6 Reaction of non-metals with oxygen and water

Non-metals react with oxygen to form non-metal oxides. Some non-metals may react with water or other substances under suitable conditions, but their general chemical behaviour differs from metals.

3. Reactivity Series

The reactivity series arranges metals in decreasing order of their reactivity.

Metals near the top lose electrons more readily and are more reactive. Metals below hydrogen generally do not displace hydrogen from dilute acids.

Using the series

• Predict whether a metal can displace another metal from its salt solution.
• Predict whether a metal can liberate hydrogen from a dilute acid.
• Understand why extraction methods differ for different metals.

4. How Do Metals and Non-metals Form Ionic Compounds?

Metals tend to lose electrons and form positive ions (cations), while non-metals tend to gain electrons and form negative ions (anions). The electrostatic attraction between oppositely charged ions forms an ionic compound.

Formation of sodium chloride

Sodium has one valence electron and chlorine needs one electron to complete its outer shell. Transfer of the electron forms Na⁺ and Cl⁻.

Properties of ionic compounds

• Usually hard and solid.
• Generally have high melting and boiling points due to strong electrostatic forces.
• Generally soluble in water and insoluble in many organic solvents.
• Conduct electricity in molten state or aqueous solution because ions are free to move.
• Do not conduct electricity well in solid state because ions are fixed in position.

5. Occurrence of Metals

Metals occur in the earth's crust in the form of minerals. A mineral from which a metal can be extracted profitably is called an ore.

Minerals and ores

All ores are minerals, but all minerals are not ores. Ores often contain unwanted earthy materials called gangue.

Metals at the top and bottom of the activity series

Very reactive metals such as potassium, sodium, calcium, magnesium and aluminium are commonly found in combined form. Less reactive metals may occur in free/native form.

6. Extraction of Metals

Basic steps of metallurgy

6.1 Concentration of ores

Ore is separated from gangue by physical or chemical methods. The aim is to increase the proportion of the useful mineral.

6.2 Extraction based on reactivity

Highly reactive metals

Potassium, sodium, calcium, magnesium and aluminium cannot be obtained by reducing their oxides with carbon. Their extraction commonly involves electrolysis.

Moderately reactive metals

Metals such as zinc, iron, lead and copper are often obtained by converting ores into oxides and then reducing the oxides using carbon or carbon monoxide.

Roasting: sulphide ores are heated strongly in excess air.

Calcination: carbonate ores are heated strongly in limited or no air.

Reduction of metal oxide:

Thermite reaction

Aluminium can reduce certain metal oxides because it has a strong affinity for oxygen. The highly exothermic thermite reaction is used for welding railway tracks and repairing cracked machine parts.

Low-reactivity metals

Metals such as mercury can be obtained from their ores by heating. Silver and gold may occur in the native state and require comparatively less extraction processing.

7. Refining of Metals

The metal obtained after extraction may contain impurities. Refining removes these impurities to obtain a purer metal.

Electrolytic refining of copper

• Anode: impure copper
• Cathode: thin sheet of pure copper
• Electrolyte: acidified copper sulphate solution
• Copper from the anode dissolves and pure copper is deposited on the cathode.
• Insoluble impurities collect below the anode as anode mud.

8. Corrosion and Its Prevention

Corrosion is the gradual deterioration of metals due to reaction with substances in the environment. Rusting of iron requires oxygen and water.

Prevention methods

• Painting
• Oiling or greasing
• Galvanisation — coating iron/steel with zinc
• Electroplating
• Alloying

Rusting experiment idea

Iron nails kept in different conditions show that both air and moisture are important for rust formation. Boiled water covered with oil limits oxygen contact, while dry air with a drying agent limits moisture.

9. Alloys

An alloy is a homogeneous mixture of two or more metals, or of a metal and a non-metal. Alloys are often made to improve hardness, strength, corrosion resistance or other useful properties.

Why alloy gold? Pure gold is very soft, so it is alloyed with other metals to make jewellery harder and more durable. The purity of gold is often expressed in carat; 24-carat gold is considered pure gold.

10. Quick Revision & Exam Focus

Must-learn equations