Cambridge IGCSE Chemistry – Chapters 1-3 Core Concepts

Flashcards covering key principles from Chapters 1 (States of matter), 2 (Atomic structure) and early Chapter 3 (Chemical bonding). Use them to test definitions, calculations, periodic trends, bonding types, mole concepts and Green Chemistry ideas.

What are the three states of matter?

Solid, liquid and gas.

Define a fluid.

A substance that can flow – i.e. a liquid or a gas.

What name is given to the temperature at which a solid turns into a liquid?

Melting point.

What happens to temperature during melting or boiling?

It stays constant until the change of state is complete.

Give the term for a solid turning directly into a gas.

Sublimation.

Why does solid carbon dioxide appear ‘dry’?

It sublimes directly to CO₂ gas without forming a liquid.

State the kinetic particle theory’s view of gases.

Gas particles are far apart, move randomly at high speed, and exert pressure by colliding with container walls.

What is diffusion?

The spreading of particles from a region of higher concentration to one of lower concentration.

Why does bromine vapour fill a gas jar left undisturbed?

Because gas particles move randomly and diffuse until evenly spread.

Which factor most affects the rate of diffusion of a gas?

Relative molecular mass – lighter molecules diffuse faster.

Name the three sub-atomic particles.

Proton, neutron and electron.

What are the relative charges of proton, neutron and electron?

+1, 0, –1 respectively.

Where are protons and neutrons found?

In the nucleus.

Define proton (atomic) number.

The number of protons in the nucleus of an atom.

Define mass (nucleon) number.

The total number of protons plus neutrons in the nucleus.

What is an isotope?

Atoms of the same element with the same proton number but different numbers of neutrons.

State two physical properties that differ between isotopes of an element.

Mass/density and rate of diffusion (some isotopes may also be radioactive).

Why do all isotopes of chlorine have identical chemical properties?

They have the same electronic configuration (same outer electrons).

What is the standard atom for relative atomic mass?

The carbon-12 isotope (¹²C).

Write the nuclear symbol for an atom of carbon-14.

₆¹⁴C

What does relative atomic mass (Ar) represent?

The weighted average mass of the naturally occurring atoms of an element on a scale where ¹²C = 12 exactly.

Calculate the Ar of chlorine if ³⁵Cl is 75% and ³⁷Cl is 25%.

(35×0.75)+(37×0.25)=35.5

State the maximum number of electrons in the first and second shells.

First shell 2; second shell 8.

Give the electronic configuration of magnesium.

2,8,2

Which period and group is magnesium in?

Period 3, Group II (2).

Why are noble gases unreactive?

Their atoms have full outer electron shells (stable configuration).

Define covalent bond.

A shared pair of electrons between two non-metal atoms.

Draw the molecular formula of water.

H₂O (two H atoms covalently bonded to one O).

How many shared electron pairs hold an O₂ molecule?

Two (a double bond).

Explain why simple molecular substances have low melting points.

They have weak intermolecular forces that require little energy to overcome.

Define ionic bond.

The strong electrostatic attraction between oppositely charged ions.

What ions are present in Na₂O?

Na⁺ and O²⁻.

Why do ionic compounds conduct electricity when molten but not solid?

Ions are free to move in the liquid but fixed in the solid lattice.

Describe metallic bonding.

Positive metal ions in a lattice attracted to a ‘sea’ of delocalised electrons.

Why are metals malleable?

Layers of ions can slide over each other while the delocalised electrons maintain bonding.

Give two giant covalent substances.

Diamond and graphite (also SiO₂).

State one use of diamond and explain why.

Cutting tools – diamond is very hard due to its 3-D network of strong covalent bonds.

Why does graphite conduct electricity?

Each carbon has one delocalised electron that moves between layers.

What is the empirical formula?

The simplest whole-number ratio of atoms in a compound.

Determine the empirical formula of a compound with 75% C and 25% H by mass.

CH₄

Define relative molecular mass (Mr).

Sum of the relative atomic masses of all atoms in a molecule.

Calculate the Mr of Ca(OH)₂ (Ca=40, O=16, H=1).

40+(2×16)+(2×1)=74

State Avogadro’s constant.

6.02 × 10²³ particles per mole.

How many moles are in 12 g of carbon-12?

1 mole.

Write the formula linking moles, mass and molar mass.

n = mass (g) ÷ M (g mol⁻¹).

What is the molar volume of any gas at r.t.p.?

24 dm³ per mole.

How many moles of gas occupy 120 dm³ at r.t.p.?

120 ÷ 24 = 5 mol.

Define concentration in mol dm⁻³.

Moles of solute per cubic decimetre of solution.

Give the equation linking moles, concentration and volume (cm³).

n = (C × V) / 1000

Explain the term ‘limiting reactant’.

The reactant that is completely used up first and thus limits the amount of product formed.

What is percentage yield?

(Actual yield ÷ theoretical yield) × 100%.

Why might percentage yield be less than 100%?

Incomplete reaction, losses in separation/transfer, side reactions.

State two principles of Green Chemistry related to stoichiometry.

Maximise atom economy; prevent waste by high percentage yield.