Year 9 Science: Waves, Thermal Energy, Atomic Structure, and Chemical Reactions

Vocabulary practice flashcards covering Year 9 Physics (sound waves, wave equations, thermal energy transfer, and energy transformations) and Chemistry (atomic structure, electron configuration, radioactivity, and chemical reactions).

Wave Motion

The transfer of energy from one point to another without the transfer of matter.

Mechanical Wave

A wave that requires a physical medium (matter) through which to travel, such as sound waves.

Transverse Wave

A wave in which the particles oscillate vertically (up and down) at right angles (perpendicular) to the direction of wave travel.

Longitudinal Wave

A wave in which the particles oscillate back and forth parallel to (in the same direction as) the movement of the wave.

Amplitude ($a$)

The distance measured from the centre rest line to the peak of a crest or the trough of a wave.

Wavelength ($\lambda$)

The distance from any point on one wave to the identical point on the adjacent wave (such as crest to crest or trough to trough), measured in metres ($\text{m}$).

Frequency ($f$)

The number of complete waves that pass a fixed reference point per unit time (usually one second), measured in hertz ($\text{Hz}$ or $\text{s}^{-1}$).

Period ($T$)

The time it takes for one complete wave cycle or wavelength to pass a point, measured in seconds ($\text{s}$) and defined by the formula $T = \frac{1}{f}$.

Compression

A high-pressure region in a longitudinal wave where medium particles are bunched closely together.

Rarefaction

A low-pressure region in a longitudinal wave where medium particles are spread farther apart.

Wave Speed Equation

The formula $v = f\lambda$, where wave speed ($v$) equals the product of wave frequency ($f$) and wavelength ($\lambda$).

Medium

The substance or material (solid, liquid, or gas) through which a wave travels. Sound travels fastest through solids, slower through liquids, and slowest through gases, and cannot travel through a vacuum.

Heat

Thermal energy that is transferred between physical systems or substances as a result of a temperature difference.

Temperature

A physical measurement of the average kinetic energy of the vibrating particles within a substance.

Methods of Heat Transfer

The three mechanisms by which thermal energy moves between systems: conduction, convection, and radiation.

Conduction

The direct transfer of thermal energy between adjacent particles in solids through particle collisions, involving no bulk matter movement or wave motion.

Convection

The transfer of thermal energy through fluids (liquids and gases) via bulk movement, wherein warmer, less dense fluid rises and cooler, denser fluid sinks.

Thermal Radiation

The transfer of heat via transverse electromagnetic waves (such as infrared) that does not require particles and can travel across a vacuum.

Electromagnetic Spectrum

The continuous range of electromagnetic waves travelling at the speed of light ($\approx 300\,000\,\text{km/s}$) in space, ordered by decreasing wavelength from radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, to gamma rays.

Thermal Conductivity

A material property measuring how effectively thermal energy is conducted through a substance; low values represent insulators (e.g., foam at $0.02\,\text{W/m}\cdot\text{K}$) and high values represent conductors.

Kinetic Energy

The energy possessed by an object due to its motion, depending directly on both the mass and the velocity of the object.

Potential Energy

Stored energy possessed by an object, which can exist as elastic, chemical, or gravitational potential energy ($\text{GPE}$).

Law of Conservation of Energy

The fundamental law stating that the total energy of an isolated system remains constant; energy cannot be created or destroyed, only transferred or transformed.

Energy Transfer

The process by which energy moves from one object or location to another without changing its form.

Energy Transformation

The process in which one form of energy is converted into one or more different forms of energy.

Energy Efficiency

The percentage of total input energy converted into useful output energy, calculated using the formula: $\text{Efficiency} = \left(\frac{\text{useful energy output}}{\text{total energy input}}\right) \times 100\%$.

Atom

The fundamental building block of all matter, consisting of a dense, positively charged nucleus surrounded by an electron cloud.

Element

A pure chemical substance composed entirely of one single type of atom, classified by atomic number on the periodic table.

Compound

A substance formed when atoms of two or more different chemical elements are chemically bonded together.

Crystal Lattice

A large, repeating grid-like three-dimensional structure formed by billions of bonded atoms in elements or compounds (e.g., silicon dioxide).

Proton

A subatomic particle in the nucleus possessing a relative electrical charge of $+1$, an atomic mass of $1\,\text{amu}$ ($1.673 \times 10^{-27}\,\text{kg}$), and whose total count determines the atomic number ($Z$).

Neutron

An electrically neutral ($0$ charge) subatomic particle located in the nucleus with a mass of $1\,\text{amu}$ ($1.675 \times 10^{-27}\,\text{kg}$).

Electron

A negatively charged ($-1$) subatomic particle orbiting the nucleus in energy levels, having a mass of approximately $\frac{1}{1800}\,\text{amu}$ ($9.109 \times 10^{-31}\,\text{kg}$).

Atomic Number ($Z$)

The number of protons found in the nucleus of an atom, defining the identity and chemical properties of an element.

Mass Number ($A$)

The total count of protons and neutrons combined in the nucleus of an atom ($\text{Mass Number} = \text{protons} + \text{neutrons}$).

Nuclear Symbol Notation

The standard scientific notation $^A_Z\text{X}$, where $\text{X}$ is the element symbol, $A$ is the superscript mass number, and $Z$ is the subscript atomic number.

Electron Shell

An energy level surrounding the nucleus where electrons orbit; each shell $n$ holds a maximum capacity of $2n^2$ electrons (first shell holds $2$, second holds $8$, third holds $18$, fourth holds $32$).

Aufbau Principle

The rule stating that electrons fill orbital shells of the lowest available energy levels closest to the nucleus before occupying higher, outer levels.

Valence Electrons

The electrons located in the outermost electron shell (valence shell) of an atom that participate directly in chemical bonding.

Excited State

The state of an atom when an electron absorbs energy (from heat or light) and jumps to a higher shell; when returning to its ground state, it releases that energy as light of a specific wavelength.

Isotope

Atoms of the exact same chemical element that contain identical numbers of protons but different numbers of neutrons in their nuclei (e.g., carbon-12, carbon-13, and carbon-14).

Radioactive Decay

The spontaneous process by which an unstable atomic nucleus releases particles or electromagnetic energy to achieve a more stable configuration.

Alpha Radiation ($\alpha$)

A form of particulate radiation consisting of two protons and two neutrons (a helium-4 nucleus) with low penetrating ability, travelling only a few centimetres in air and stopped by skin or paper.

Beta Radiation ($\beta$)

A nuclear decay emission consisting of a high-speed electron ejected when a neutron in the nucleus converts into a proton, stopped by thin sheets of aluminium.

Gamma Radiation ($\gamma$)

High-frequency electromagnetic ionizing radiation emitted by an unstable nucleus that possesses high penetrating power, requiring dense lead or thick concrete shielding.

Penetrating Ability of Radiation

The relative capacity of nuclear emissions to pass through matter: alpha particles are stopped by paper/skin, beta particles penetrate through skin but are stopped by aluminium, and gamma rays penetrate aluminium but are attenuated by lead or concrete.

Half-Life

The time required for half the radioactive nuclei in a given sample of a radioisotope to decay into more stable products (e.g., $5730\,\text{years}$ for carbon-14).

Irradiation

The process of exposing objects or biological tissue to beams of radiation to sterilise instruments or destroy cancerous tumor cells.

Chemical Reaction

A process where bonds between atoms in reactant substances are rearranged to form chemically distinct new products.

Reactants

The starting materials that undergo chemical change during a reaction, written on the left side of a chemical equation.

Products

The new substances formed as the outcome of a chemical reaction, written on the right side of a chemical equation.

State Symbols

Letters written in parentheses indicating the physical state of substances in a chemical equation: $(s)$ for solid, $(l)$ for liquid, $(g)$ for gas, and $(aq)$ for aqueous solution.

Composition Reaction

A chemical reaction in which two or more simpler reactants combine together to synthesize a single compound ($\text{A} + \text{B} \rightarrow \text{AB}$).

Decomposition Reaction

A chemical reaction in which a single compound breaks down into two or more smaller product molecules or elements ($\text{AB} \rightarrow \text{A} + \text{B}$).

Law of Conservation of Mass

A fundamental principle of chemistry stating that mass is neither created nor destroyed in a chemical reaction; the total mass and the number of each kind of atom in the reactants must equal those in the products.

Coefficient and Subscript

In a balanced chemical equation, coefficients are the full-sized numbers placed in front of formulas to balance atom totals across the reaction, whereas subscripts are fixed small numbers showing the internal atom ratios of chemical compounds.