Chemistry Notes, Ch 1 & 2 (0620 & 0971, CIE IGCSE)

Here are brief notes for IGCSE Chemistry, syllabus codes 0620 and 0971 to help you ace your exams!

For a set of IGCSE Chemistry past papers, click here.

Chapter 1: States of Matter

🔑 Key Concepts

• Matter exists in three physical states: solid, liquid, and gas.
• The properties of these states are explained by the particle model.
• Changes in state involve changes in the arrangement and energy of particles.

Key Terms	Definitions
Matter	Anything that has mass and takes up space.
Solid	A state of matter with a fixed shape and volume. Particles are tightly packed and vibrate in place.
Liquid	A state of matter with a fixed volume but no fixed shape. Particles are close but can slide past each other.
Gas	A state of matter with no fixed shape or volume. Particles are far apart and move freely.
Particle Model	A theory that explains the properties of solids, liquids, and gases based on the arrangement and movement of particles.
Melting	The change of state from solid to liquid.
Boiling	The rapid change of state from liquid to gas throughout the liquid at its boiling point.
Freezing	The change of state from liquid to solid.
Evaporation	The gradual change of state from liquid to gas at the surface of a liquid below its boiling point.
Condensation	The change of state from gas to liquid.
Sublimation	The change of state directly from solid to gas without passing through the liquid state.
De-sublimation or Deposition	The change of state directly from gas to solid.
Diffusion	The spreading of particles from an area of higher concentration to an area of lower concentration.
Kinetic Theory	A theory that explains how the energy and movement of particles relate to the states of matter.
Compressibility	The ability to be compressed or made smaller in volume. Gases are easily compressible; solids and liquids are not.
Energy of Particles	A measure of the movement of particles. Solids have low energy, liquids have more, and gases have the most.
Intermolecular Forces	Forces between particles that determine how strongly they attract each other. Strong in solids, weaker in liquids, very weak in gases.
Brownian Motion	Random movement of particles suspended in a fluid, evidence for particle movement and existence.

🔬 The Three States of Matter

Property	Solid	Liquid	Gas
Surface boundary	Yes (strong forces of attraction)	Yes (weaker forces of attraction)	No (weakest forces of attraction)
Shape	Fixed	Takes shape of container	Takes shape of container
Volume	Fixed	Fixed	Not fixed (can expand/compress)
Compressibility	Not compressible	Slightly compressible	Easily compressible
Particle arrangement	Tightly packed in fixed positions	Close together but can move	Far apart, move freely
Particle movement	Vibrate around fixed positions	Slide slowly past each other	Move rapidly in all directions
Forces between particles	Very strong	Weak	Very weak
Energy of particles	Low	Moderate	High

⚙️ The Particle Model

• All matter is made of tiny particles (atoms, molecules, or ions).
• The behavior of particles explains the properties of solids, liquids, and gases.
• As temperature increases, particle energy increases, affecting motion and arrangement

🔄 Changes of State

Change of State	Process Name
Solid ➝ Liquid	Melting
Liquid ➝ Solid	Freezing
Liquid ➝ Gas	Boiling/Evaporation
Gas ➝ Liquid	Condensation
Solid ➝ Gas	Sublimation
Gas ➝ Solid	Deposition

Notes for Changes of State:

• Melting Point: The temperature at which a solid turns into a liquid.
• Boiling Point: The temperature at which a liquid turns into a gas throughout the liquid (not just the surface).
• Evaporation: Takes place at the surface of a liquid and at any temperature.

🌡️ Kinetic Theory of Matter

• Describes how particles move depending on temperature and energy.
• Solids: Particles vibrate around fixed positions.
• Liquids: Particles move around each other.
• Gases: Particles move freely and rapidly in all directions.

🔥 Effect of Temperature on the Volume of a Gas

(At constant pressure)

• As temperature increases, gas particles move faster (they gain kinetic energy).
• They collide more often and with more force against the walls of the container.
• To keep pressure constant, the volume increases to allow space for these more energetic collisions.

Conclusion:
🔺 Temperature → 🔺 Volume

This is described by Charles’s Law:

“At constant pressure, the volume of a fixed mass of gas is directly proportional to its absolute temperature (in kelvin).”

🎈 Effect of Pressure on the Volume of a Gas

(At constant temperature)

• Increasing pressure pushes gas particles closer together.
• Since the temperature (and therefore particle energy) remains constant, reducing the space (volume) forces the particles to collide more often in a smaller area.

Conclusion:
🔺 Pressure → 🔻 Volume
🔻 Pressure → 🔺 Volume

This is described by Boyle’s Law:

“At constant temperature, the volume of a fixed mass of gas is inversely proportional to its pressure.”

💨 Diffusion

Definition: The movement of particles from an area of higher concentration to an area of lower concentration.

Examples of Diffusion:

1. In gases: A gas spreads out to fill the entire space available (e.g., perfume scent in a room).
2. In liquids: A drop of ink spreads in water.

Factors affecting diffusion:

• Temperature: Higher temperature = faster diffusion.
• Particle mass: Lighter particles diffuse faster.

⚠️ Diffusion is evidence for:

• The existence of small particles.
• The movement of particles.

🧪 Experiments Demonstrating States of Matter

1. Bromine Gas Diffusion
   • A gas jar of bromine is placed above a gas jar of air.
   • Over time, the bromine diffuses down, showing gas particles move.
2. Potassium Permanganate in Water
   • A few crystals added to water spread through the liquid, showing diffusion in liquids.

🔍 Summary of Chapter 1

• All substances are made of particles which are constantly in motion.
• The arrangement, movement, and energy of particles differ across solids, liquids, and gases.
• Diffusion supports the particle theory of matter.
• Changing state involves gaining or losing energy, not creating or destroying particles.

Chapter 2: Atoms, Elements and Compounds

🔑 Key Concepts

• Structure of atoms
• Elements, compounds and mixtures
• Writing formulas and equations
• Ionic and covalent bonding basics
• Oxidation and reduction
• Isotopes and relative atomic mass

Key Terms	Definitions
Atom	The smallest part of an element that can take part in chemical reactions.
Element	A substance made of only one type of atom. It cannot be broken down into simpler substances by chemical means.
Compound	A substance formed when two or more elements are chemically bonded together.
Mixture	A combination of two or more substances that are not chemically bonded and can be separated by physical methods.
Proton	A positively charged subatomic particle found in the nucleus of an atom.
Neutron	A subatomic particle with no charge found in the nucleus of an atom.
Electron	A negatively charged subatomic particle that orbits the nucleus in shells.
Nucleus	The dense center of an atom that contains protons and neutrons.
Relative Mass	A comparison of the mass of subatomic particles (proton = 1, neutron = 1, electron ≈ 0).
Relative Charge	The electric charge relative to a proton (+1).
Proton Number (Atomic Number)	The number of protons in the nucleus of an atom; it defines the element.
Nucleon Number (Mass Number)	The total number of protons and neutrons in the nucleus of an atom.
Isotope	Atoms of the same element that have the same number of protons but different numbers of neutrons.
Relative Atomic Mass (Aᵣ)	The weighted average mass of an atom of an element compared with one-twelfth of the mass of a carbon-12 atom.
Electronic Structure	The arrangement of electrons in shells (energy levels) around the nucleus.
Ion	A charged particle formed when an atom gains or loses electrons.
Cation	A positively charged ion (formed when an atom loses electrons).
Anion	A negatively charged ion (formed when an atom gains electrons).
Ionic Bond	A strong electrostatic attraction between oppositely charged ions.
Covalent Bond	A bond formed when two atoms share a pair of electrons.
Molecule	Two or more atoms covalently bonded together.
Empirical Formula	The simplest whole-number ratio of atoms of each element in a compound.
Molecular Formula	The actual number of atoms of each element in a molecule.
Chemical Formula	A representation showing the elements in a compound and the ratio of atoms.
Word Equation	A representation of a chemical reaction using names of substances.
Symbol Equation	A representation using chemical symbols and formulas.
State Symbols	Indicators showing physical states: (s), (l), (g), (aq).
Oxidation	Gain of oxygen or loss of electrons.
Reduction	Loss of oxygen or gain of electrons.
Redox Reaction	A chemical reaction in which oxidation and reduction occur simultaneously.
Oxidising Agent	A substance that causes oxidation by accepting electrons.
Reducing Agent	A substance that causes reduction by donating electrons

What is an Element?

• A pure substance made of only one type of atom.
• Cannot be broken down into simpler substances by chemical means.
• Each element is represented by a unique chemical symbol (e.g. H for hydrogen, O for oxygen, C for carbon).
• All elements are listed in the Periodic Table.

🧠 Example:
Oxygen (O) is an element because it contains only oxygen atoms.

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🔹 What is an Atom?

The smallest part of an element that can take part in chemical reactions.

🧬 Atomic Structure

• Atoms are neutral overall and made of subatomic particles:
  • Nucleus: Contains protons (positive) and neutrons (neutral).
  • Electrons: Negatively charged particles that orbit the nucleus in shells.

Relative Masses and Charges in an Atom

Particle	Relative Mass	Relative Charge	Location
Proton	1	+1	Nucleus
Neutron	1	0	Nucleus
Electron	~0 (1/1836)	-1	Shells around nucleus

🔢 Atomic and Mass Numbers

• Proton Number (top): Number of protons; defines the element. There are 6 protons in Carbon (element symbol = C)
• Nucleon Number/Atomic Mass (bottom): Total number of protons + neutrons. There are 12 protons and nucleons in Carbon. To derivce the number of nuetrons, subtract total protons from Atomic Mass, i.e. 12 – 6 protonos = 6 neutrons

📊 Table 2.1 – Classification of Elements

Property	Metals	Non-metals
Physical state at room temperature	Solid (except mercury)	Solid, liquid (bromine only), or gas
Malleability	Good	Poor (usually soft or brittle)
Ductility	Good	Poor (usually soft or brittle)
Appearance	Shiny (lustrous)	Usually dull
Melting and boiling point	Usually high	Usually low
Density	Usually high	Usually low
Electrical and thermal conductivity	Good	Poor (except graphite)