4.9 Comparison of General Physical Properties of Metals and Non-Metals

This topic compares the general physical properties of metals and non-metals, focusing on thermal conductivity, electrical conductivity, malleability and ductility, and melting and boiling points.

Definition

Metals are elements that tend to lose electrons and form positive ions (cations). They are found on the left and middle of the periodic table.

Non-metals are elements that tend to gain or share electrons. They are found on the right side of the periodic table.

Simple explanation: Metals are on the left; non-metals are on the right. They have very different physical properties.

Main Idea

The book compares metals and non-metals based on four physical properties:

• Thermal conductivity
• Electrical conductivity
• Malleability and ductility
• Melting and boiling points

Simple explanation: Metals and non-metals differ in how they conduct heat, conduct electricity, can be shaped, and melt/boil.

Core Concept

Comparison Table

Detailed Explanation

1. Thermal Conductivity

Metals generally have high thermal conductivity, which means they can conduct heat easily.

Non-metals tend to have poor conductivity, making them less efficient at conducting heat.

Simple explanation: Metals are good at carrying heat; non-metals are not.

• Metals: Copper, aluminium, silver — used in cooking pans.
• Non-metals: Wood, plastic, rubber — used as heat insulators.

2. Electrical Conductivity

Metals are good conductors of electricity because they have free electrons that can move freely in the metal lattice.

Non-metals, with few exceptions such as graphite, are poor conductors of electricity because they lack free electrons.

Simple explanation: Metals have free electrons that carry electric current; most non-metals do not.

• Metals: Copper, silver, gold — used in electrical wiring.
• Non-metals: Sulfur, phosphorus, iodine — insulators.
• Exception: Graphite (a non-metal) conducts electricity because it has delocalized electrons.

3. Malleability and Ductility

• Malleable → can be hammered into thin sheets.
• Ductile → can be drawn into wires.

This property is due to metallic bonds, which allow atoms to exchange easily under pressure.

Non-metals are neither malleable nor ductile — rather, they are brittle.

Simple explanation: Metals can be shaped; non-metals break when hit.

• Metals: Gold leaf (malleable), copper wires (ductile).
• Non-metals: Sulfur, phosphorus — break easily when hit.

4. Melting Points and Boiling Points

Metals generally have high melting points and boiling points due to strong metallic bonds that require a lot of energy to break.

• covalent bonds
• van der Waals bonds
• hydrogen bonds

These require less energy to break.

Simple explanation: Metals have strong bonds → high melting/boiling points. Non-metals have weaker forces → lower melting/boiling points.

• Metals: Iron (1538 °C), Tungsten (3422 °C).
• Non-metals: Sulfur (115 °C), Iodine (114 °C).

Intermediate Level

Why Metals Conduct Electricity

Metals have free (delocalized) electrons that can move freely through the metal lattice. When a voltage is applied, these electrons flow, carrying electric current.

Non-metals generally lack free electrons (their electrons are tightly held in covalent bonds), so they do not conduct electricity.

Exception: Graphite (a non-metal) has delocalized electrons between its layers, so it does conduct electricity.

Why Metals Are Malleable and Ductile

In metals, atoms are held together by metallic bonds — a "sea" of delocalized electrons surrounding positive metal ions.

• When a force is applied, the layers of atoms can slide over each other.
• The metallic bond is not broken — the delocalized electrons hold the atoms together.
• So metals can be shaped without breaking.

Non-metals are brittle because their atoms are held by directional covalent bonds — when a force is applied, these bonds break, and the material shatters.

Why Metals Have High Melting Points

Metals have strong metallic bonds — the attraction between positive metal ions and delocalized electrons.

• These bonds are strong.
• A lot of energy is needed to break them.
• So metals have high melting and boiling points.

• Covalent bonds within molecules are strong.
• But intermolecular forces (van der Waals, hydrogen bonds) are weak.
• So less energy is needed to melt/boil them.
• Hence non-metals have lower melting/boiling points.

Exception — Graphite

Graphite is a non-metal that conducts electricity and heat because it has delocalized electrons between its layers. This is an important exception to the general rule.

Exception — Diamond

Diamond is a non-metal with a very high melting point (~3550 °C) because it has a giant covalent structure with strong covalent bonds throughout. This is another exception.

Important Points

• - Metals: high thermal conductivity, good electrical conductivity, malleable and ductile, high melting/boiling points.
• - Non-metals: poor thermal conductivity, poor electrical conductivity (except graphite), brittle, lower melting/boiling points.
• - Metals conduct electricity because of free electrons.
• - Non-metals generally lack free electrons.
• - Metals are malleable and ductile because of metallic bonds.
• - Non-metals are brittle because of directional covalent bonds.
• - Metals have high melting/boiling points due to strong metallic bonds.
• - Non-metals have lower melting/boiling points due to weaker intermolecular forces.
• - Exceptions: Graphite (conducts electricity), diamond (very high melting point).

Remember

• - Metals: good conductors, malleable, ductile, high melting/boiling points.
• - Non-metals: poor conductors (except graphite), brittle, lower melting/boiling points.
• - Metals conduct because of free electrons.
• - Metals are malleable/ductile because of metallic bonds.
• - Non-metals are brittle because of covalent bonds.
• - Metals have high melting points because of strong metallic bonds.
• - Non-metals have lower melting points because of weaker intermolecular forces.
• - Exception: Graphite conducts electricity.

Common Mistakes

• 1. Thinking all non-metals are poor conductors. Graphite is a non-metal that conducts electricity.
• 2. Thinking all metals have the same melting point. They vary widely (mercury is liquid at room temperature).
• 3. Thinking non-metals are always gases. Some are solids (sulfur, phosphorus, iodine).
• 4. Confusing malleability and ductility. Malleable = can be hammered into sheets; ductile = can be drawn into wires.
• 5. Thinking non-metals are always brittle. Some non-metals (like diamond) are very hard, though still brittle.
• 6. Forgetting the role of metallic bonds. Metallic bonds explain why metals conduct and are malleable.

Quick Revision

• Thermal conductivity: metals high; non-metals poor.
• Electrical conductivity: metals good (free electrons); non-metals poor (except graphite).
• Malleability and ductility: metals malleable and ductile (metallic bonds); non-metals brittle.
• Melting and boiling points: metals generally high (strong metallic bonds); non-metals generally lower (weaker intermolecular forces).
• Exceptions: graphite conducts electricity; diamond has a very high melting point.

60-Second Revision

• Metals: good conductors, malleable, ductile, high melting points.
• Non-metals: poor conductors (except graphite), brittle, lower melting points.
• Metals conduct because of free electrons.
• Metals are malleable because of metallic bonds.
• Warning: graphite is a non-metal that conducts electricity — an exception.