Metals and Non-Metals
Chapter 3 · Complete Study Notes · Science Learning Hub
1. Introduction
Metals and non-metals are important parts of our daily lives. Metals such as iron and copper have different properties and uses, while non-metals such as oxygen, carbon and sulphur also have different properties and uses.
Examples: iron, copper, aluminium, gold and silver.
Examples: oxygen, carbon and sulphur.
2. Physical Properties
Physical properties are characteristics of a substance that can be observed without changing its chemical nature.
A. Metals
- Lustre: Metals generally have a shiny and reflective surface called metallic lustre.
- Hardness: Iron and copper are hard at room temperature, whereas sodium is so soft that it can be cut with a knife.
- Malleability: The ability of a metal to be beaten into thin sheets. Gold and silver are among the most malleable metals.
- Ductility: The property by which metals can be drawn into thin wires. Gold is the most ductile metal; about 2 km of wire can be drawn from 1 g of gold.
- Conduction of heat and electricity: Metals are generally good conductors. Silver and copper are the best conductors of heat. Lead and mercury are comparatively poor conductors of heat. Electric wires are coated with PVC or a rubber-like material.
- Sonority: The property of producing a ringing sound when struck against a hard surface.
- Melting and boiling points: Metals generally have high melting points. Gallium and caesium have very low melting points.
B. Non-metals
- Lack of lustre: Most non-metals are dull. Iodine is a lustrous non-metal.
- Poor conduction: Non-metals are generally poor conductors of heat and electricity. Graphite, an allotrope of carbon, conducts electricity.
- Brittleness: Many solid non-metals are brittle; they are neither malleable nor ductile. Sulphur and phosphorus are examples.
- Variety of states: Non-metals occur in all three states at room temperature: oxygen is a gas, bromine is a liquid and sulphur is a solid.
Summary: Metals vs Non-metals
| Property | Metals | Non-metals |
|---|---|---|
| Lustre | Lustrous (shiny surface) | Generally dull; iodine is an exception |
| Hardness and state | Generally hard solids; sodium and potassium are soft; mercury is liquid | May be solids, liquids or gases; solid forms may be brittle |
| Malleability and ductility | Generally malleable and ductile | Generally neither malleable nor ductile |
| Electrical conduction | Good conductors; silver and copper are excellent | Poor conductors; graphite is an exception |
| Melting and boiling points | Generally high; gallium and caesium are exceptions | Generally low; diamond is an exception |
3. Chemical Properties of Metals
Metals can be more clearly distinguished from non-metals on the basis of their chemical properties.
(a) Reaction of metals with air
Metals combine with oxygen in the air to form metal oxides.
- Sodium and potassium react vigorously with air and may catch fire. They are stored under kerosene.
- Magnesium, aluminium, zinc and lead develop a thin oxide layer that prevents further oxidation.
- Iron filings burn vigorously on heating, although a large piece of iron does not burn easily.
- Copper forms copper oxide when heated.
- Silver and gold do not react with oxygen even at high temperatures.
Nature of metal oxides
Most metal oxides are basic. Aluminium oxide and zinc oxide show both acidic and basic behaviour and are called amphoteric oxides. They react with both acids and bases to form salt and water.
(b) Reaction of metals with water
Some metals react with water to form metal hydroxides or metal oxides and hydrogen gas. All metals do not react with water.
Cold water
- Potassium and sodium react violently with cold water. The reaction is highly exothermic, and hydrogen may catch fire.
- Calcium reacts less violently and starts floating because hydrogen bubbles stick to its surface.
- Magnesium does not react appreciably with cold water. It reacts with hot water to form magnesium hydroxide and hydrogen.
Steam
Aluminium, iron and zinc react with steam to form metal oxides and hydrogen.
Lead, copper, silver and gold do not react with water under ordinary conditions.
(c) Reaction of metals with dilute acids
Copper does not react with dilute hydrochloric acid because it is below hydrogen in the reactivity series.
Aqua regia
Aqua regia is a freshly prepared mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio 3:1. It can dissolve gold even though neither acid can dissolve gold separately. Aqua regia is highly corrosive.
(d) Reaction with solutions of other metal salts
A more reactive metal can displace a less reactive metal from its salt solution.
Iron displaces copper because iron is more reactive than copper.
Copper cannot displace iron because copper is less reactive than iron.
Reactivity Series
The reactivity series is a list of metals arranged in the order of their decreasing chemical activity.
| Symbol | Element | Relative reactivity |
|---|---|---|
| K | Potassium | Most reactive |
| Na | Sodium | High |
| Ca | Calcium | High |
| Mg | Magnesium | Medium |
| Al | Aluminium | Medium |
| Zn | Zinc | Medium |
| Fe | Iron | Medium |
| Pb | Lead | Medium |
| H | Hydrogen | Non-metal reference line |
| Cu | Copper | Low |
| Hg | Mercury | Low |
| Ag | Silver | Least reactive |
| Au | Gold | Least reactive |
4. How do Metals and Non-metals React?
Reactivity is the tendency of an element to attain a stable electronic configuration. Metals generally lose electrons from their valence shell to form positively charged ions called cations. Non-metals generally gain electrons to form negatively charged ions called anions.
Formation of sodium chloride (NaCl)
Sodium has one electron in its outermost shell. It loses this electron and forms Na⁺.
A neutral sodium atom has 11 protons and 11 electrons. After losing one electron, it has 10 electrons.
Chlorine has seven electrons in its outermost shell. It accepts one electron and forms Cl⁻.
A neutral chlorine atom has 17 protons and 17 electrons. After gaining one electron, it has 18 electrons.
The oppositely charged sodium and chloride ions attract one another and form sodium chloride. Sodium chloride exists as a three-dimensional arrangement of oppositely charged ions held together by strong electrostatic forces, not as separate molecules.
Formation of magnesium chloride (MgCl₂)
Magnesium loses two electrons to form Mg²⁺, while each chlorine atom gains one electron to form Cl⁻.
5. Ionic Compounds
Compounds formed by the transfer of electrons from a metal to a non-metal are called ionic compounds or electrovalent compounds.
Properties of ionic compounds
- Physical nature: Generally hard crystalline solids because of strong attraction between oppositely charged ions. They are brittle and may break into fragments when pressure is applied.
- Melting and boiling points: High, because considerable energy is needed to overcome strong inter-ionic attractions.
- Solubility: Generally dissolve in water but do not dissolve in non-polar solvents such as kerosene or petrol.
- Conduction of electricity: Solid ionic compounds do not conduct electricity because their ions are fixed. In the molten state or aqueous solution, ions become free to move and conduct electricity.
6. Occurrence and Extraction of Metals
The earth's crust is the major source of metals. Seawater also contains soluble salts such as sodium chloride and magnesium chloride. Some metals occur in the free state, while others occur as compounds. Gold, silver, platinum and copper can be found in the free state. Copper and silver can also occur in the combined state.
Elements or compounds that occur naturally in the earth's crust.
Minerals that contain a high percentage of a particular metal and from which the metal can be extracted profitably.
Main stages of extraction
- Enrichment of ores: Removal of unwanted impurities (gangue) from the ore.
- Extraction of metals: Conversion of the concentrated ore into the metal.
- Refining of metals: Purification of the extracted metal.
Gangue means unwanted materials such as soil and sand mixed with ores. Enrichment processes are based on differences in physical or chemical properties of the ore and gangue.
Extraction of metals low in the activity series
These metals are very unreactive. Their oxides can be reduced to metals by heating alone.
Extraction of metals in the middle of the activity series
Metals such as iron, zinc, lead and copper have moderate reactivity. Their sulphide and carbonate ores are first converted into oxides.
- Roasting: Sulphide ores are heated strongly in excess air to convert them into oxides.
- Calcination: Carbonate ores are heated strongly in limited air to convert them into oxides.
Metal oxides are reduced using suitable reducing agents such as carbon.
Highly reactive metals such as sodium, calcium and aluminium can displace less reactive metals from their compounds.
Extraction of metals towards the top of the activity series
Highly reactive metals cannot be obtained by heating their oxides with carbon because they have a stronger attraction for oxygen than carbon has. Sodium, magnesium and calcium are obtained by electrolysis of their molten chlorides, whereas aluminium is obtained by electrolytic reduction of aluminium oxide.
- During electrolysis, the metal is deposited at the cathode (negatively charged electrode).
- Chlorine gas is liberated at the anode (positively charged electrode).
Key metallurgy terms
| Term | Meaning |
|---|---|
| Gangue | Unwanted impurities such as soil and sand present in an ore. |
| Roasting | Converting sulphide ores into oxides by heating strongly in excess air. |
| Calcination | Converting carbonate ores into oxides by heating strongly in limited air. |
| Reduction | Converting metal oxide into metal using a reducing agent such as carbon. |
Refining of metals
Metals produced by reduction contain impurities. A widely used method is electrolytic refining, used for copper, zinc, tin, nickel, silver and gold.
- Anode: Impure copper metal.
- Cathode: Thin strip of pure copper metal.
- Electrolyte: Acidified copper sulphate solution.
When electric current passes through the electrolyte, copper from the impure anode dissolves into the solution and an equivalent amount of pure copper is deposited on the cathode. Soluble impurities go into solution, while insoluble impurities settle at the bottom as anode mud.
7. Corrosion
The surface of some metals, such as iron, is corroded when exposed to moist air for a long period. This phenomenon is known as corrosion.
Examples of corrosion
- Silver: Becomes black when exposed to air because it reacts with sulphur compounds to form a coating of silver sulphide.
- Copper: Reacts with moist carbon dioxide in air and develops a green coating of basic copper carbonate.
- Iron: Exposed to moist air develops a brown, flaky coating called rust.
Prevention of corrosion
Rusting of iron can be prevented by painting, oiling, greasing, galvanising, chrome plating, anodising or alloying.
Galvanisation: Protecting iron and steel from rusting by coating them with a thin layer of zinc. The galvanised article is protected against rusting even if the zinc coating is broken.
Alloying: Mixing a metal with other elements in suitable proportions to improve its properties.
8. Alloys
An alloy is a homogeneous mixture of two or more metals, or of a metal and a non-metal. To prepare an alloy, the main metal is melted, other elements are added in suitable proportions and the mixture is cooled.
Pure iron is soft and stretches easily when heated. Adding a small amount of carbon (about 0.05%) makes it hard and strong. Adding nickel and chromium produces stainless steel, which is hard and resistant to rust.
| Alloy / Material | Composition | Properties and uses |
|---|---|---|
| Steel / hardened iron | Iron + 0.05% carbon | Hard and strong compared to soft pure iron |
| Stainless steel | Iron + nickel + chromium (+ carbon) | Hard and highly resistant to rust |
| Brass | Copper + zinc | Lower electrical conductivity than pure copper |
| Bronze | Copper + tin | Lower electrical conductivity than pure copper |
| Solder | Lead + tin | Low melting point; used for joining electrical wires |
| Amalgam | Metal + mercury | Mercury-based alloy mixture |
Electrical conductivity and purity of gold
- Alloys generally have lower electrical conductivity and lower melting points than the pure metals from which they are made. Brass and bronze are poorer conductors than pure copper. Solder has a low melting point and is used for joining electrical wires.
- Pure gold is called 24-carat gold. It is very soft and malleable, making it unsuitable for jewellery. It is alloyed with silver or copper to increase hardness.
- In India, 22-carat gold is commonly used for ornaments; it contains 22 parts of pure gold and 2 parts of silver or copper.
Quick Revision – Important Points
Malleability, ductility, lustre, sonority and conductivity.
Aluminium oxide (Al₂O₃) and zinc oxide (ZnO).
More reactive metals displace less reactive metals from salt solutions.
Metals form cations by losing electrons; non-metals form anions by gaining electrons.
Both air and water are required for rusting of iron.
Homogeneous mixtures of metals, or a metal and a non-metal.
Important formulae and reactions
- Metal + oxygen → metal oxide
- Metal + dilute acid → salt + hydrogen
- Metal + water → metal hydroxide / oxide + hydrogen
- Metal A + salt solution of metal B → salt solution of metal A + metal B (when A is more reactive)
- Fe₂O₃ + 2Al → 2Fe + Al₂O₃ + heat (thermite reaction)
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