Year 9 Science: Chemistry, Atomic Bonds, Climate Change, and Energy Efficiency

Comprehensive practice flashcards defining core terms in chemistry, chemical bonding, organic compounds, climate systems, and electrical energy efficiency.

Hydrocarbon

A chemical compound consisting of only carbon and hydrogen atoms.

Alkane

The simplest class of hydrocarbons, characterized by single covalent bonds between carbon atoms with each carbon atom bonded to four other atoms.

Alkene

A hydrocarbon containing at least one double covalent bond between carbon atoms.

Alkyne

A hydrocarbon containing at least one triple covalent bond between carbon atoms.

Complete Combustion

A reaction occurring when there is plenty of oxygen, allowing every carbon and hydrogen atom to fully oxidize, producing carbon dioxide ($CO_2$) and water ($H_2O$) while releasing maximum energy.

Incomplete Combustion

A reaction occurring when oxygen supply is limited, preventing full oxidation and producing carbon monoxide ($CO$), unburnt carbon powder called soot ($C$), water ($H_2O$), and reduced energy.

Intermolecular Forces

Electrostatic forces existing between separate molecules that are much weaker than intramolecular bonds and govern physical state transitions such as melting and boiling points.

Net Dipole Moment

The overall vector sum of all individual bond dipoles in a molecule, reflecting an asymmetric charge distribution where one end is partially positive and the other partially negative.

London Dispersion Forces

Weak intermolecular attractions present in non-polar molecules arising from momentary, instantaneous dipole moments caused by the constant motion of electrons.

Dipole-Dipole Forces

Intermolecular forces in polar molecules originating from electrostatic attractions between the partially positive pole of one molecule and the partially negative pole of an adjacent molecule.

Alcohol

An organic compound derived from a hydrocarbon where a hydrogen atom is replaced by a hydroxyl group ($-OH$), designated with the suffix -ol.

Hydration of Alkenes

A chemical reaction where water adds across the carbon-carbon double bond of an alkene to produce an alcohol.

Hydroformylation

Also called the oxo reaction, a chemical process in which an alkene reacts with synthesis gas (a mixture of carbon monoxide and hydrogen) in the presence of a catalyst to produce an aldehyde.

Aldehyde

An organic compound featuring a carbonyl carbon atom bonded to a hydrogen atom, double-bonded to an oxygen atom, and single-bonded to another atom or group of atoms.

Dehydration of Alcohols

A reversible reaction where an alcohol is converted into an alkene and water using an acid catalyst such as sulfuric or phosphoric acid, exhibiting a reactivity order of $3^\circ > 2^\circ > 1^\circ$.

Isomer

Compounds that share the identical molecular formula but have different structural arrangements of their atoms.

Addition Polymerisation

A reaction process wherein monomer molecules containing double bonds add sequentially to reactive centres without forming by-products, producing high-molecular-mass polymers.

Free Radical

A highly reactive atom, molecule, or ion containing at least one unpaired valence electron.

Thermosoftening Plastics

Plastics (such as polyethene) that can be repeatedly melted down and reshaped using heat and pressure due to their high molecular mass polymer chains.

Thermosetting Plastics

Plastics formed through an irreversible chemical process that cannot be melted or reshaped once cured, such as epoxy resin.

Benzene

An aromatic hydrocarbon with the molecular formula $C_6H_6$, structured as a planar hexagon with bond lengths of $140\,pm$, bond angles of $120^\circ$, $sp^2$ hybridized orbitals, and a delocalized pi electron system.

Plum Pudding Model

An atomic model proposed by J.J. Thomson in which negatively charged electrons are embedded throughout a uniform sphere of positive charge.

Rutherford Alpha Particle Scattering Experiment

An experiment where alpha particles were directed at thin gold foil; most passed through undeflected while a small fraction experienced substantial deflection, proving the atom has a tiny, dense, positively charged nucleus.

Bohr Atomic Model

The 1913 model by Niels Bohr proposing that electrons travel around the atomic nucleus in fixed orbits of defined energy levels, analogous to planets orbiting the Sun.

Neutron

An uncharged subatomic particle discovered in 1932 by Thomas Chadwick by bombarding beryllium with alpha particles, possessing approximately the same mass as a proton.

Octet Rule

The chemical principle that atoms gain, lose, or share electrons during bonding to obtain a stable valence shell of 8 electrons (or 2 in the first shell).

Ionic Bond

A chemical bond resulting from the electrostatic attraction between oppositely charged ions formed through the complete transfer of valence electrons from a metal to a non-metal.

Cation

A positively charged ion formed when a neutral atom loses one or more valence electrons.

Anion

A negatively charged ion formed when a neutral atom gains one or more valence electrons.

Polyatomic Ion

A covalently bonded group of two or more atoms that carries an overall net electrical charge and acts as a single chemical unit in reactions.

Covalent Bond

A chemical bond formed when two non-metal atoms achieve complete outer electron shells by sharing pairs of valence electrons.

Metallic Bond

The electrostatic attraction between positively charged metal cations and a surrounding, delocalized 'sea' of freely moving valence electrons shared across the lattice.

Combination Reaction

A chemical reaction in which two or more reactants combine to form a single product ($A + B \rightarrow AB$), such as the Haber process ($N_2(g) + 3H_2(g) \rightarrow 2NH_3(g)$).

Decomposition Reaction

A chemical reaction in which a single reactant breaks down into two or more distinct products ($AB \rightarrow A + B$).

Law of Conservation of Mass

The law stating that mass is neither gained nor lost in a closed system, meaning the total number and mass of atoms remain constant throughout a chemical reaction.

Single Displacement Reaction

A chemical reaction in which a single uncombined element replaces another element in a compound ($AB + C \rightarrow CB + A$), such as copper displacing silver in aqueous silver nitrate.

Climate

The long-term average atmospheric conditions—including temperature, precipitation, wind, and humidity—recorded in a given region over an extended period, typically 30 years.

Weather

The day-to-day mix of atmospheric phenomena—including air pressure, wind speed, temperature, and humidity—occurring at a particular time and place in the troposphere.

Troposphere

The lowest layer of Earth's atmosphere, located closest to the surface, in which almost all weather events occur.

Convection Cell

A large-scale atmospheric circulation loop where warm air rises at regions of low pressure and cool dry air descends at regions of high pressure, with three cells operating per hemisphere.

Ozone Layer

A concentrated region of ozone ($O_3$) in the stratosphere that absorbs all short-wave UV-C radiation, $90\%$ of medium-wave UV-B, and transmits roughly $50\%$ of long-wave UV-A.

Chlorofluorocarbons (CFCs)

Synthetic compounds formerly used in refrigeration and aerosols that deplete stratospheric ozone by reacting with $O_3$ to yield oxygen ($O_2$) and chlorine monoxide ($ClO$).

Enhanced Greenhouse Effect

The intensified warming of Earth's lower atmosphere and surface caused by increased concentrations of greenhouse gases emitted by human activities such as burning fossil fuels.

Carbon Sink

Any natural reservoir or process—such as oceans or terrestrial vegetation—that absorbs and stores carbon dioxide from the atmosphere.

Ice Cores

Cylindrical samples drilled from ice sheets in Greenland and Antarctica containing trapped air bubbles used by scientists to reconstruct past atmospheric gas concentrations and historical temperatures.

Ocean Conveyor Belt

A global system of interconnected warm surface currents and cold deep density-driven currents connecting four of the five oceans, completing a full cycle in approximately $1,000\text{ years}$.

Ocean Salinity

The concentration of dissolved salts in ocean water, averaging $35\,g/kg$, which along with temperature governs seawater density.

Ocean Waterfalls

Massive sinking flows of cold, dense, saline water in the North Atlantic and Southern Ocean triggered by winter sea ice formation, which drives deep global ocean circulation.

Circuit Component Symbols

Standard schematic diagrams used to represent electrical parts in circuit drawings, such as switches, thermistors, lamps, cells, ammeters, voltmeters, diodes, inductors, batteries, resistors, and light-dependent resistors.

Open System

A thermodynamic system capable of freely exchanging both matter and energy across its boundaries with the surrounding environment.

Closed System

A thermodynamic system that allows energy to be transferred into or out of its surroundings, but prevents any exchange of matter.

Isolated System

A thermodynamic system bounded such that neither energy nor matter can enter or leave, maintaining a constant total internal energy.

Energy Efficiency

A calculated measure of the proportion of total input energy successfully transformed into useful output energy, expressed as $\text{efficiency } (\%) = \frac{\text{useful output energy}}{\text{total input energy}} \times 100$.

Ohm's Law

The physical law stating that current ($I$) through a conductor is directly proportional to applied voltage ($V$) and inversely proportional to resistance ($R$), expressed as $V = I \times R$.

Sankey Diagram

A flow diagram illustrating energy transfers where arrow widths reflect energy proportions, showing total energy input entering on the left, useful outputs travelling horizontally, and wasted energy descending downward.

Watt

The standard unit of electrical power measuring energy transformation at a rate of one joule per second ($1\,W = 1\,J/s$).

Kilowatt-hour (kWh)

A unit of electrical energy representing the total energy transformed by a one-kilowatt ($1000\,W$) appliance operating continuously for one hour.

Series Circuit

An electrical circuit configuration offering only a single linear pathway for current flow, where voltage is shared among components and any break opens the entire circuit.

Parallel Circuit

An electrical circuit configuration containing multiple branches, where each branch receives full supply voltage, total current divides across branches, and a break in one path does not interrupt current in others.