Year 9 Exam Revision - Chemistry and Physics

What is an atom?

The smallest particle of an element that retains the properties of that element. Made up of protons, neutrons and electrons.

What is the atomic number?

The number of protons in the nucleus. Identifies the element.

What is the mass number?

The total number of protons and neutrons.

Where are protons found?

In the nucleus. Charge = +1, Relative mass = 1.

Where are neutrons found?

In the nucleus. Charge = 0, Relative mass = 1.

Where are electrons found?

In electron shells around the nucleus. Charge = -1, Relative mass = 1/1836.

What are isotopes?

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

What is an ion?

An atom that has gained or lost electrons and therefore has an electrical charge.

What is a cation?

A positive ion formed when electrons are lost.

What is an anion?

A negative ion formed when electrons are gained.

What is an ionic compound?

A compound formed when a metal transfers electrons to a non-metal. Opposite charges attract.

What is a chemical reaction?

Bonds between atoms are broken and new bonds form, producing at least one new substance. Atoms are rearranged but not created or destroyed.

What are the signs of a chemical reaction?

Permanent colour change, gas produced, temperature change, precipitate formed, light emitted, change in physical properties.

What is activation energy?

The minimum amount of energy needed to start a chemical reaction.

Sources of activation energy?

Heat, light, electricity, flame.

What is an exothermic reaction?

A reaction that releases energy to the surroundings. Heat energy EXITS the system.

Memory trick for exothermic reactions?

EXO = EXIT.

What is an endothermic reaction?

A reaction that absorbs energy from the surroundings. Heat energy ENTERS the system.

Memory trick for endothermic reactions?

ENDO = ENTER.

What is an acid?

A substance that donates hydrogen ions (H+).

Properties of acids?

Sour, corrosive, conduct electricity, pH less than 7.

What is a base (alkali)?

A substance that accepts hydrogen ions (H⁺).

Properties of bases?

Bitter, slippery, conduct electricity, pH greater than 7.

What is neutralisation?

A reaction between an acid and a base that produces salt and water.

What is a dilute solution?

A solution containing a small amount of solute and a large amount of solvent.

What is a concentrated solution?

A solution containing a large amount of solute and a small amount of solvent.

What does the pH scale measure?

The strength of acids and bases on a scale from 0–14.

What does a change of 1 pH unit represent?

A tenfold change in acidity.

What is radioactivity?

The spontaneous decay of unstable nuclei to become more stable.

What is alpha radiation?

A particle consisting of 2 protons and 2 neutrons. Charge = +2. Stopped by paper.

What is beta radiation?

A fast-moving electron. Charge = -1. Stopped by aluminium.

What is gamma radiation?

Electromagnetic radiation with no mass and no charge. Stopped by thick lead or concrete.

What is half-life?

The time taken for half of the radioactive atoms in a sample to decay.

What is energy?

The ability to do work or cause change.

State the law of conservation of energy.

Energy cannot be created or destroyed. It can only be transferred or transformed.

What is energy transfer?

The movement of energy from one object or place to another.

What is energy transformation?

The conversion of energy from one form to another.

What is kinetic energy?

The energy of movement.

What is gravitational potential energy?

Energy stored because of an object's height above the ground.

What is elastic potential energy?

Energy stored when an object is stretched or compressed.

What is chemical energy?

Energy stored in chemical bonds.

What is thermal energy?

Energy associated with the movement of particles.

What is electrical energy?

Energy carried by moving electric charges.

What is sound energy?

Energy carried by vibrations.

What is light energy?

Energy carried by electromagnetic waves.

What is conduction?

Heat transfer through direct contact without movement of matter.

What is convection?

Heat transfer by the movement of fluids.

What is a convection current?

Circular movement in fluids caused by differences in density. Warm fluid rises and cool fluid sinks.

How do convection currents transfer heat?

Warm fluid rises, cool fluid sinks, creating a continuous cycle.

What is radiation?

Heat transfer by electromagnetic waves. No particles are needed.

What is evaporation?

The change from liquid to gas, transferring energy into the atmosphere.

How do winds transfer energy?

Energy moves with moving air.

How do ocean currents transfer energy?

Energy moves with moving water around Earth.

What is a wave?

A disturbance that transfers energy without transferring matter.

What is a crest?

The highest point of a transverse wave.

What is a trough?

The lowest point of a transverse wave.

What is amplitude?

The maximum displacement from equilibrium. Greater amplitude = louder sound.

What is wavelength?

The distance between two corresponding points on a wave.

What is frequency?

The number of waves passing a point each second.

What is 1 hertz (Hz)?

One cycle per second.

What is a transverse wave?

A wave that vibrates at right angles to the direction of travel.

Examples of transverse waves?

Light and electromagnetic waves.

What is a longitudinal wave?

A wave that vibrates parallel to the direction of travel.

Example of a longitudinal wave?

Sound.

What are compressions?

Regions where particles are close together.

What are rarefactions?

Regions where particles are spread apart.

What is a mechanical wave?

A wave that requires a medium.

What is an electromagnetic wave?

A wave that does not require a medium and can travel through space.

What is electromagnetic radiation (EMR)?

Energy that travels through space as electromagnetic waves.

How are electromagnetic waves produced?

Changing electric fields create magnetic fields, and changing magnetic fields create electric fields.

Why are radio waves useful for communication?

They travel at the speed of light, have long wavelengths, diffract around obstacles and can be reflected by the ionosphere.

Uses of radio waves?

Radio, television, GPS, mobile networks.

Uses of microwaves?

Wi-Fi, satellite TV, satellite communication and 5G networks.

What is a geostationary satellite?

A satellite that remains above the same point on Earth. Height = 35,800 km, orbit time = 24 hours.

Uses of geostationary satellites?

TV broadcasts, weather observations, navigation.

What is a Low Earth Orbit (LEO) satellite?

A satellite that orbits close to Earth at 160-2000 km and takes 90-120 minutes to orbit.

Uses of LEO satellites?

Satellite internet, satellite phones and Earth imaging.

How do fibre-optic cables send information?

Infrared light travels along optical fibres by reflection and information is carried as digital pulses.

Why are fibre-optic cables reliable?

Signals are transmitted as ON/OFF pulses and are less affected by noise.

Compare fibre internet and satellite internet.

Fibre is faster, more reliable and has lower delay. Satellite works in remote areas but has higher delay.

What is electric current?

The flow of electric charge. Symbol = I. Unit = Ampere (A).

What is voltage?

The energy transferred per unit charge that pushes charges around a circuit. Unit = Volt (V).

What is resistance?

Opposition to current flow. Unit = Ohm (Ω).

What is a conductor?

A material that allows electrons to move easily. Examples: copper, aluminium, gold.

What is a closed circuit?

A complete path with no breaks so current can flow.

What is an open circuit?

A circuit containing a break so current cannot flow.

What is Direct Current (DC)?

Current that flows in one direction. Used in batteries and electronics.

What is Alternating Current (AC)?

Current that changes direction repeatedly. Used in homes and businesses.

What is a hypothesis?

A prediction that can be tested through investigation.

What is an independent variable?

The variable changed by the scientist.

What is a dependent variable?

The variable measured in an investigation.

What are controlled variables?

Variables kept the same to ensure a fair test.

What is accuracy?

How close a measurement is to the true value.

What is precision?

How close repeated measurements are to one another. It measures consistency.

What is an error?

The difference between a measured value and the true value.

What is a random error?

An error with no pattern. Can be reduced by repeating measurements and averaging.

What is a systematic error?

An error that follows a pattern and consistently shifts results too high or too low.

What is reliability?

The ability to obtain the same results when an investigation is repeated.

What is repeatability?

Obtaining the same results when the same person repeats an experiment.

What is reproducibility?

Obtaining the same results when a different person repeats an experiment.