Exam practice

Both come from the same cause: the layers of atoms can slide over one another while the free electrons hold them together.

In a metal, the atoms are held together by metallic bonds: positive ions sit in a sea of free electrons that belong to the whole piece of metal. When the metal is hammered or pulled, layers of ions slide over one another, but the free electrons move with them and keep holding them together. So the metal changes shape without breaking: it is malleable and ductile.

The atoms of a metal are held together by strong attractive forces (metallic bonds). To melt the metal, or to boil it, a lot of energy must be supplied to overcome these forces, so the metal must be heated to a high temperature.

A child may bite and break the glass. The sharp glass can cut the mouth, and the mercury inside is poisonous: its vapor is absorbed through the lungs and damages the brain, nerves and kidneys, and children are the most easily harmed. A digital thermometer is safer, or the thermometer can be held under the arm.

1. Metals have a shine (luster).
2. They are mostly hard.
3. They are good conductors of heat and electricity.
4. They are sonorous: they ring when struck.
5. They are malleable: they can be beaten into sheets.
6. They are ductile: they can be drawn into wires.
7. They mostly have high melting and boiling points.
8. They are solid at room temperature (except mercury).

Make a simple circuit with a dry cell, a torch bulb in a holder and connecting wires, leaving a gap between two bare ends A and B. Place different things across the gap one at a time: a copper wire, an aluminium wire, an iron nail, a coin, and then a piece of wood, paper, sulphur and coal.

Observation: the bulb glows when the copper wire, aluminium wire, iron nail or coin is placed across the gap, but not with wood, paper, sulphur or coal.

Conclusion: current flows through the metals and completes the circuit, but not through the non-metals. So metals are good conductors of electricity. (They conduct because they contain free electrons, which can flow.)

1. Metals react with oxygen to form basic oxides:

2Mg + O₂ → 2MgO
2. Reactive metals react with dilute acids to form a salt and hydrogen gas:

Zn + H₂SO₄ → ZnSO₄ + H₂
3. Very reactive metals react with water to form a metal hydroxide (an alkali) and hydrogen gas:

2Na + 2H₂O → 2NaOH + H₂

Mercury:

1. It damages the brain and nervous system (trembling, memory loss), especially in children.
2. It damages the kidneys and lungs, and can harm a baby in the womb, as it crosses the placenta.

Lead:

1. It slows the development of a child’s brain, causing learning problems and changes in behavior.
2. It causes anemia; and stored in the bones in place of calcium, it weakens them and interferes with the making of blood cells.