Comprehensive theory, key formulas, diagrams, and memory aids for Materials: Metals and Non-Metals.
All objects around us — from the spoon we use to the pencil we write with — are made of materials, and these materials can be broadly divided into two groups: metals and non-metals. Metals are materials like iron, copper, gold, aluminium and silver that we associate with strength and shine, while non-metals include gases like oxygen and nitrogen, solids like sulphur, carbon and phosphorus, and liquids like bromine. About 118 elements are known today, of which roughly 22 are non-metals and the rest are metals.
We use different materials for different purposes precisely because they behave differently. A copper wire carries electricity, while a plastic covering insulates it; an iron nail is hard and strong, while charcoal (a form of carbon) crumbles easily. The properties that decide how and where a material is used — physical and chemical — are the subject of this chapter. Understanding these properties explains why metals and non-metals are used so differently in everyday life.
Physical properties can be observed without changing the material into a new substance. The important physical properties are:
Chemical properties describe how a material reacts with other substances. The important chemical properties are:
When a metal reacts with a non-metal, an ionic compound is formed. For example, sodium (a metal) reacts with chlorine (a non-metal) to form sodium chloride (common salt). In this reaction, the metal atom loses electrons to become a positively charged ion (cation), and the non-metal atom gains electrons to become a negatively charged ion (anion). The oppositely charged ions are held together by strong electrostatic forces, forming a crystal lattice.
These ionic compounds have characteristic properties: they are usually crystalline solids, have high melting and boiling points, and conduct electricity when dissolved in water or melted. Ordinary salt, calcium oxide (quicklime) and magnesium chloride are all examples of ionic compounds formed by the reaction of metals with non-metals.
Metals and non-metals are used according to their properties:
Uses of metals: - Iron is used for making machines, tools and buildings. - Copper and aluminium are used for electrical wires and cooking utensils because they are good conductors and ductile. - Aluminium is light and is used in aeroplanes, foils and utensils. - Gold and silver are used for jewellery because of their lustre and resistance to corrosion. - Zinc is used for galvanising iron to prevent rusting. - Mercury is used in thermometers.
Uses of non-metals: - Oxygen is essential for breathing and combustion. - Nitrogen is used in fertilisers and to preserve food. - Hydrogen is used in the manufacture of ammonia and rocket fuel. - Carbon (in the form of graphite) is used as a lubricant and in pencil leads, while diamond is used for cutting glass and in jewellery. - Sulphur is used in making sulphuric acid, matches and gunpowder. - Chlorine is used for purifying water.
Metals are not found freely in nature (except less reactive ones like gold and silver); they are obtained from naturally occurring minerals called ores. An ore is a mineral from which a metal can be extracted profitably. For example, haematite is an ore of iron, bauxite is an ore of aluminium, and cinnabar is an ore of mercury.
Many metals react with air and moisture and get damaged over time. Rusting is the slow chemical change in which iron reacts with oxygen and moisture in the air to form a brown, flaky substance called rust. Rusting weakens iron objects. The rusting of iron requires both oxygen and moisture (or water). Methods to prevent rusting include: - Painting the surface to keep air and moisture away. - Applying oil or grease on tools and machine parts. - Galvanisation: coating iron with a layer of zinc. - Tinning: coating iron with tin (as in tin cans). - Coating with plastic or enamel. - Alloying: mixing iron with other metals (making stainless steel).
Sometimes the properties of a metal are not enough, so we mix it with other metals or non-metals to get a more useful material. An alloy is a homogeneous mixture of two or more metals, or a metal and a non-metal. Alloys are usually stronger, harder and more resistant to corrosion than the pure metals.
Alloying is a smart way to combine the best properties of different materials into one.
| Property | Metals | Non-Metals |
|---|---|---|
| State | Solid (except mercury) | Solid, liquid or gas |
| Lustre | Lustrous (shiny) | Dull (except iodine, diamond) |
| Hardness | Generally hard | Generally soft (except diamond) |
| Malleability | Malleable (beat into sheets) | Non-malleable, break when beaten |
| Ductility | Ductile (drawn into wires) | Not ductile |
| Conduction | Good conductors of heat and electricity | Poor conductors (except graphite) |
| Sonority | Sonorous (ringing sound) | Not sonorous |
| Reaction | Metals | Non-Metals |
|---|---|---|
| With oxygen | Form basic oxides | Form acidic or neutral oxides |
| With water | Release hydrogen (some metals) | Generally no reaction |
| With dilute acids | Release hydrogen gas | Generally no reaction |
| With bases | Some release hydrogen | Generally no reaction |
| Alloy | Composition | Uses |
|---|---|---|
| Stainless steel | Iron + chromium + nickel | Utensils, surgical instruments |
| Brass | Copper + zinc | Decorative items, musical instruments |
| Bronze | Copper + tin | Statues, medals |
| Amalgam | Mercury + another metal | Dental fillings |
graph TD
A["Materials: Metals and Non-Metals"] --> B["Physical Properties"]
B --> B1["Lustre, hardness, malleability, ductility"]
B --> B2["Conduction of heat and electricity"]
B --> B3["Sonority, state"]
A --> C["Chemical Properties"]
C --> C1["React with oxygen: basic vs acidic oxides"]
C --> C2["React with water and acids: release hydrogen"]
C --> C3["Reactivity series"]
A --> D["Metals + Non-Metals"]
D --> D1["Ionic compounds (e.g. NaCl)"]
A --> E["Rusting and Prevention"]
E --> E1["Painting, oiling, galvanisation"]
E --> E2["Alloying, tinning"]
A --> F["Alloys"]
F --> F1["Stainless steel, brass, bronze"]
Metals and non-metals differ in almost every physical and chemical property — in lustre, hardness, malleability, ductility, conduction, sonority, and in how they react with oxygen, water and acids. These differences decide their uses: metals for wires, utensils, tools and jewellery, and non-metals for fertilisers, fuels, medicines and water purification. The reaction between a metal and a non-metal produces ionic compounds such as sodium chloride, which make up so many important substances around us. The menace of rusting can be controlled through painting, oiling, galvanisation and alloying. By understanding the properties of materials, we can choose the right material for the right purpose and protect our metal articles for longer.