IGCSE Chemistry Atoms, elements and compounds topical questions

The list shows four substances: iron, water, air, carbon dioxide.

1. (a)Which substance is an element?[1]
2. (b)Which substances are compounds?[2]
3. (c)Which substance is a mixture?[1]

An atom of carbon-12 has 6 protons and 6 neutrons. State the number of electrons and the number of neutrons in this atom.

Complete the sentences about the particles inside an atom.

1. (a)State the relative charge of a neutron.[1]
2. (b)Name the particle that has a relative mass of approximately zero.[1]
3. (c)Name the particle found in the shells around the nucleus.[1]

Magnesium has proton number 12 and mass number 24.

1. (a)Write the electronic configuration of a magnesium atom.[1]
2. (b)Magnesium forms a 2+ ion. Explain how the ion forms and write its electronic configuration.[2]
3. (c)State the group and the period of magnesium in the Periodic Table.[1]

Chlorine has two isotopes, chlorine-35 and chlorine-37.

1. (a)State the meaning of the term isotope.[1]
2. (b)Explain why the two isotopes have the same chemical properties.[2]

Sodium reacts with oxygen to form sodium oxide, Na₂O.

1. (a)Write the electronic configuration of an oxygen atom (proton number 8).[1]
2. (b)Use electronic configurations to explain why the formula of sodium oxide is Na₂O.[2]
3. (c)Write the formula of the oxide ion, including its charge.[1]

Bromine exists as two isotopes, ⁷⁹₃₅Br and ⁸¹₃₅Br.

1. (a)State the proton number of bromine and explain what it tells you.[2]
2. (b)State the number of neutrons in an atom of each isotope.[1]
3. (c)Explain why the two isotopes have identical chemical properties.[1]

A sample of boron contains 20% boron-10 and 80% boron-11 by abundance.

1. (a)Calculate the relative atomic mass of this sample of boron.[2]
2. (b)Explain why the relative atomic mass is not a whole number.[2]

Two solid forms of carbon are diamond and graphite.

1. (a)Explain, in terms of structure, why diamond is extremely hard.[2]
2. (b)Graphite is soft and conducts electricity. Explain both properties using its structure.[2]

Three substances have these properties. Substance A is a gas at room temperature and never conducts electricity. Substance B melts at 801 °C and conducts when molten but not when solid. Substance C conducts electricity even when solid.

1. (a)State the type of structure and bonding shown by each substance.[3]
2. (b)Explain why substance B conducts when molten.[1]
3. (c)Suggest one substance that could be C.[1]