1. Physical Properties of Metals and Non-metals

Physical Properties of Metals

Metals generally show the following physical properties:

• Metallic lustre: Pure metals usually have a shining surface.
• Hardness: Most metals are hard, although hardness varies. Sodium and potassium are soft enough to be cut with a knife.
• Malleability: Metals can be beaten into thin sheets. Gold and silver are highly malleable.
• Ductility: Metals can be drawn into thin wires. Gold is highly ductile.
• Conductivity: Metals generally conduct heat and electricity well. Silver and copper are among the best conductors of heat.
• Sonority: Metals produce a ringing sound when struck. This is why manufacturers use metals to make bells.
• Physical state: Most metals are solids at room temperature. Mercury is an important exception because it is liquid.

Physical Properties of Non-metals

Non-metals usually show properties opposite to those of metals.

• They may exist as solids or gases at room temperature. Bromine is a liquid non-metal.
• They are generally dull, brittle and non-sonorous.
• They are not malleable or ductile.
• They generally conduct heat and electricity poorly.

2. Chemical Properties of Metals

2.1 Reaction of Metals with Oxygen

Most metals combine with oxygen to form metal oxides. Metal oxides are generally basic in nature.

Magnesium burns in air with a dazzling white flame and forms magnesium oxide.

Copper reacts with oxygen on heating and forms black copper(II) oxide.

Aluminium reacts with oxygen to form aluminium oxide.

Basic and Amphoteric Oxides

Most metal oxides show basic behaviour. However, some metal oxides react with both acids and bases to produce salts and water. These oxides are called amphoteric oxides.

Examples: Aluminium oxide (Al₂O₃) and zinc oxide (ZnO).

Aluminium oxide reacts with hydrochloric acid:

It also reacts with sodium hydroxide:

Some metal oxides dissolve in water to form alkalis.

Why Do Sodium and Potassium Need Careful Storage?

Sodium and potassium react vigorously with oxygen and moisture. They may catch fire when exposed to air. Therefore, we store them under kerosene oil to prevent contact with air and water.

Protective Oxide Layer

Magnesium, aluminium, zinc and lead can develop a thin oxide layer on their surfaces. This layer protects the metal from further oxidation. Aluminium develops a protective aluminium oxide coating. Anodising makes this oxide layer thicker and improves its resistance to corrosion.

2.2 Reaction of Metals with Water

Depending on their reactivity, metals react differently with cold water, hot water or steam. These reactions may produce a metal hydroxide or metal oxide along with hydrogen gas.

Potassium reacts with water as follows:

Sodium reacts with water as follows:

Calcium reacts with water as follows:

Aluminium reacts with steam as follows:

Iron reacts with steam as follows:

3. Reaction of Metals with Acids

Many metals react with dilute acids to form a salt and hydrogen gas.

Magnesium, aluminium, zinc and iron react with dilute hydrochloric acid. The rate of reaction varies with the metal. In the NCERT activity, magnesium reacts most vigorously among the tested metals, followed by aluminium, zinc and iron.

Copper does not react with dilute hydrochloric acid under these conditions because it is less reactive than hydrogen.

Aqua Regia

Aqua regia is a freshly prepared mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio of 3:1. It can dissolve gold and platinum, even though neither acid can dissolve these metals alone.

4. Displacement Reactions and the Reactivity Series

Displacement Reaction

A more reactive metal displaces a less reactive metal from its salt solution. This reaction helps us compare the reactivity of metals.

Iron displaces copper from copper sulphate solution because iron is more reactive than copper.

Zinc displaces iron from iron(II) sulphate solution.

Copper displaces silver from silver nitrate solution.

The Reactivity Series

The reactivity series arranges metals in decreasing order of their chemical activity. A metal near the top is generally more reactive than a metal below it.

5. How Do Metals and Non-metals React?

Atoms tend to attain a stable electronic configuration. Metals generally lose electrons and form positively charged ions called cations. Non-metals generally gain electrons and form negatively charged ions called anions.

Formation of Sodium Chloride

A sodium atom loses one electron and forms a sodium ion. A chlorine atom gains that electron and forms a chloride ion. The oppositely charged ions attract each other and form sodium chloride (NaCl).

Formation of Magnesium Chloride

Magnesium loses two electrons to form Mg²⁺. Each chlorine atom gains one electron, so two chlorine atoms are needed to form MgCl₂.

Compounds formed through electron transfer from metals to non-metals are called ionic compounds or electrovalent compounds.

Properties of Ionic Compounds

1. Physical nature: Ionic compounds are generally solid, hard and brittle.
2. Melting and boiling points: They usually have high melting and boiling points because strong electrostatic forces hold their ions together.
3. Solubility: They are generally soluble in water and insoluble in solvents such as kerosene and petrol.
4. Electrical conductivity: They do not conduct electricity in the solid state because their ions cannot move freely. They conduct electricity when molten or dissolved in water, where their ions can move.

6. Occurrence and Extraction of Metals

Minerals, Ores and Gangue

• Minerals: Naturally occurring elements or compounds found in the Earth's crust.
• Ores: Minerals that contain a sufficiently high percentage of a metal for profitable extraction.
• Gangue: Unwanted impurities such as soil and sand found mixed with ores.
• Metallurgy: The process of extracting metals from their ores and refining them for use.

Extraction Depends on Reactivity

The reactivity of a metal determines the method used to extract it from its ore.

Enrichment of Ores

Ores contain gangue, which must be removed before extracting the metal. The method depends on differences between the physical or chemical properties of the ore and the impurities.

Roasting

Roasting converts sulphide ores into oxides by heating them strongly in excess air.

Calcination

Calcination converts carbonate ores into oxides by heating them strongly in limited air.

Reduction of Metal Oxides

We can reduce some metal oxides using carbon. For example, zinc oxide reacts with carbon to produce zinc.

The Thermit Reaction

Aluminium can reduce iron(III) oxide to iron. This highly exothermic reaction releases enough heat to produce molten iron. The thermit reaction can join railway tracks and repair cracked machine parts.

Electrolytic Reduction

Highly reactive metals such as sodium, magnesium, calcium and aluminium cannot be extracted from their oxides by heating with carbon. Their compounds require electrolytic reduction.

During the electrolysis of molten sodium chloride:

7. Electrolytic Refining of Metals

Metals obtained after extraction may contain impurities. Electrolytic refining removes these impurities and produces purer metal.

In copper refining, impure copper forms the anode, a thin strip of pure copper forms the cathode, and acidified copper sulphate solution acts as the electrolyte.

8. Corrosion and Its Prevention

Corrosion occurs when metals slowly react with substances in their surroundings, such as air and moisture. Corrosion can damage metal objects and change their appearance.

• Rusting of iron: Iron develops a brown, flaky coating when exposed to moist air over time.
• Tarnishing of silver: Silver reacts with sulphur compounds in the air and develops a black coating of silver sulphide.
• Green coating on copper: Copper reacts with moist carbon dioxide in air and develops a green coating of basic copper carbonate.

Conditions Required for Rusting

The NCERT activity compares iron nails in three test tubes. Nails exposed to both air and water rust, while nails kept away from air or moisture do not rust under the test conditions.

Methods to Prevent Corrosion

• Painting: Keeps air and moisture away from the metal.
• Oiling and greasing: Create a protective barrier.
• Galvanisation: Coats iron or steel with zinc.
• Chrome plating: Provides a protective surface coating.
• Anodising: Thickens the protective oxide layer on aluminium.
• Alloying: Changes a metal's properties to improve resistance to corrosion.

Galvanisation protects iron and steel from rusting by coating them with zinc. The zinc layer can continue to protect the iron even if the coating gets scratched, because zinc is more reactive than iron.

9. Alloys

An alloy is a homogeneous mixture of two or more metals, or of a metal and a non-metal. Manufacturers prepare alloys to improve properties such as strength, hardness and resistance to corrosion.

Pure iron is relatively soft and stretches easily when hot. Adding a small amount of carbon makes it harder and stronger. Adding chromium and nickel produces stainless steel, which resists rusting.

Gold Alloys

Pure gold, or 24-carat gold, is soft and is not ideal for making jewellery. Adding copper or silver makes it harder. The NCERT chapter explains that 22-carat gold contains 22 parts pure gold mixed with 2 parts of another metal.

Amalgam

An alloy that contains mercury is called an amalgam.

10. Chemical Properties of Non-metals

Non-metals show chemical behaviour that differs from metals. They generally gain electrons when they react with metals and form negatively charged ions.

Reaction with Oxygen

Most non-metals form acidic or neutral oxides when they combine with oxygen. For example, sulphur burns in oxygen to form sulphur dioxide.

Sulphur dioxide dissolves in water and forms an acidic solution. The NCERT activity asks students to test this solution with red and blue litmus paper.

Non-metals do not generally displace hydrogen from dilute acids. They can react with hydrogen to form hydrides.

11. Important Chemical Equations for Quick Revision