RBSE Secondary Science key terms

A reaction in which two or more substances join to form a single new product, such as calcium oxide combining with water to give slaked lime, usually releasing heat.

A reaction in which one compound breaks down into two or more simpler substances, often driven by heat, light, or electricity, as when calcium carbonate is heated to give lime and carbon dioxide.

A reaction in which a more reactive element pushes a less reactive element out of its compound, for example iron nails turning copper sulphate solution green as copper is displaced.

A reaction in which two ionic compounds swap partners to form two new compounds, often producing an insoluble precipitate, as when sodium sulphate solution meets barium chloride solution.

A reaction in which one substance loses electrons (oxidation) while another gains them (reduction) at the same time, such as copper oxide being reduced by hydrogen to copper.

The loss of electrons by a substance, or its gain of oxygen, during a chemical change; burning magnesium in air and rusting of iron are everyday examples of this process.

A numbered scale from 0 to 14 that expresses how acidic or basic a solution is, with values below 7 acidic, 7 neutral, and above 7 basic.

The reaction between an acid and a base that produces a salt and water and brings the pH towards 7, as when hydrochloric acid is added to sodium hydroxide solution.

A dye or substance that changes colour according to whether the solution it is added to is acidic or basic, helping to detect the endpoint of a titration.

A ranking of metals in order of how readily they lose electrons and react, from potassium and sodium at the top down to gold at the bottom, used to predict displacement reactions.

A metal oxide that behaves as both an acid and a base depending on what it reacts with; aluminium oxide and zinc oxide dissolve in acids and in alkalis alike.

A mixture of a metal with one or more other elements, made to improve properties such as hardness or resistance to corrosion; brass, bronze, and steel are common examples.

The slow wearing away of a metal by chemical attack from its surroundings, most familiar as the rusting of iron in moist air, which needs both oxygen and water.

A family of carbon compounds with the same general formula and similar chemical properties, in which successive members differ by one CH2 unit, as in alkanes or alcohols.

The particular atom or group of atoms within a carbon compound that determines its characteristic reactions and properties, such as the –OH group of alcohols or –COOH of carboxylic acids.

One of two or more compounds that share the same molecular formula but have different arrangements of atoms and therefore different properties, such as ethanol and dimethyl ether.

The principle that the properties of elements are a periodic function of their atomic masses; Mendeleev arranged elements by mass and left gaps for elements not yet discovered.

A chart arranging elements in order of increasing atomic number so that elements with similar properties fall into the same vertical group and show repeating trends across each period.

A mode of feeding in which an organism makes its own food from simple inorganic substances using light energy, as green plants do through photosynthesis in their chloroplasts.

Tiny pores, mainly on the underside of leaves, that open and close to let carbon dioxide in and oxygen and water vapour out, controlled by surrounding guard cells.

The breakdown of glucose with oxygen inside cells to release energy, producing carbon dioxide and water; it supplies most of the energy used by animals and plants.

Millions of tiny balloon-like air sacs at the ends of bronchioles in the lungs, where their thin, moist, richly supplied walls allow efficient exchange of oxygen and carbon dioxide with blood.

The microscopic filtering unit of the kidney; each one filters blood under pressure and reabsorbs useful substances such as glucose and water, leaving urine behind.

A rapid, automatic response to a stimulus that does not wait for a decision from the brain, such as pulling your hand away from a hot object through a spinal reflex arc.

The tiny gap between the end of one nerve cell and the start of the next, across which a chemical signal diffuses to pass the impulse onward.

A plant hormone produced in the growing tips of shoots that makes cells elongate; it moves towards the shaded side, bending the shoot towards light in a phototropic response.

The transfer of pollen grains from the anther of a flower to the stigma, carried by wind, water, or animals, and a necessary step before fertilisation can occur.

The fusion of a male gamete with a female gamete to form a zygote, which is the first cell of a new individual in both plants and animals.

The form of a characteristic that appears in a hybrid organism even when only one copy of its gene is present, masking the recessive form of the same trait.

The particular combination of genes an organism carries for a characteristic, written as pairs of letters, which together with the environment produces the visible trait.

The process by which individuals better suited to their surroundings survive and leave more offspring, so helpful inherited variations become more common in later generations.

The formation of a new species when populations become reproductively isolated and accumulate different variations over many generations until they can no longer interbreed.

The bending of light as it passes at an angle from one transparent medium into another of different optical density, caused by a change in the speed of light.

A number expressing how much a medium slows light compared with a vacuum, equal to the ratio of the speed of light in vacuum to that in the medium.

A lens thicker in the middle than at the edges that converges a parallel beam of light to a focus, forming real images used in cameras and in correcting long sight.

Short-sightedness, a defect in which distant objects look blurred because the eye lens focuses images in front of the retina; corrected by a concave lens of suitable power.

The statement that the current through a metallic conductor is directly proportional to the potential difference across it, provided its temperature stays constant.

The opposition a conductor offers to the flow of electric current, measured in ohms; it increases with length and temperature and decreases with greater cross-sectional area.

A circuit in which components are connected one after another in a single path, so the same current flows through each and the supply voltage divides between them.

The production of a potential difference in a conductor when the magnetic field around it changes, the principle behind dynamos and electric generators.

A device in which a current-carrying coil in a magnetic field experiences forces that turn it, converting electrical energy into the mechanical energy of rotation.

A long coil of insulated wire that produces a strong, uniform magnetic field along its axis when current flows, behaving like a bar magnet with two poles.

The warming of the Earth because gases such as carbon dioxide and methane trap outgoing heat radiation, a natural process now strengthened by human emissions from burning fuels.

The thinning of the ozone layer in the upper atmosphere by gases such as chlorofluorocarbons, allowing more harmful ultraviolet radiation to reach the Earth's surface.

A natural resource that is naturally replenished within a human lifetime, such as sunlight, wind, flowing water, or biomass, unlike coal and petroleum which are finite.

Meeting present needs without compromising the ability of future generations to meet theirs, by using resources wisely, reducing waste, and protecting ecosystems.

A factor in an experiment that is deliberately kept the same across all trials so that any change in the results can be attributed to the variable being tested.

A testable, predictive statement about how two variables are related, framed before the experiment and then checked against the evidence collected.

Information gathered directly through the senses or instruments during an investigation, recorded exactly as it appears before any interpretation is made.