Chemistry Vocabulary in English

An atom is the smallest unit of a chemical element that still has the chemical properties of that element. Atoms consist of a nucleus (containing protons and neutrons) surrounded by electrons. A molecule is formed when two or more atoms are chemically bonded together. Water (H₂O) is a molecule made of two hydrogen atoms and one oxygen atom. All molecules are made of atoms, but not all atoms are in molecules — noble gases like helium exist as single atoms.

Oxidation is a chemical process in which a substance loses electrons (or gains oxygen). Reduction is the opposite — a substance gains electrons (or loses oxygen). These two processes always occur together in what chemists call a redox reaction: one substance is oxidised while another is reduced simultaneously. The mnemonic OIL RIG is commonly taught in English-speaking schools: Oxidation Is Loss, Reduction Is Gain (of electrons).

pH is a scale from 0 to 14 that measures the acidity or alkalinity (basicity) of a solution. A pH of 7 is neutral (like pure water). Values below 7 are acidic (lemon juice is about pH 2, stomach acid is pH 1–2). Values above 7 are alkaline or basic (baking soda is about pH 9, bleach is pH 12–13). pH matters in medicine, agriculture, water treatment, food science, and swimming pools — all of which require careful pH control.

A compound is a pure substance in which two or more elements are chemically bonded in fixed proportions. The properties of a compound differ from its component elements — water (H₂O) is very different from hydrogen gas and oxygen gas. A mixture contains two or more substances that are physically combined but not chemically bonded. The components of a mixture can be separated by physical means like filtering, evaporation, or distillation.

A catalyst is a substance that increases the rate of a chemical reaction without being permanently consumed in the process. Catalysts work by providing an alternative reaction pathway with a lower activation energy — the energy needed to start the reaction. This allows more molecules to react at a given temperature. Industrial catalysts are crucial in the manufacture of fertilisers, fuels, and plastics. Biological catalysts, called enzymes, drive the reactions of life.

An acid is a substance that donates hydrogen ions (H⁺) in solution and has a pH below 7. Bases (also called alkalis in solution) accept hydrogen ions and have a pH above 7. When an acid and a base react, they neutralise each other to form a salt and water. This neutralisation reaction is important in digestion, environmental science (acid rain), and laboratory chemistry.

Electrolysis uses an electric current to drive a non-spontaneous chemical reaction. In industry, electrolysis is used to extract pure metals from their ores (for example, aluminium from bauxite), to electroplate metals (coating objects with a thin layer of another metal like gold or chrome), and to produce chemicals such as chlorine and sodium hydroxide from salt water. Electrolysis of water produces hydrogen and oxygen gases, which is relevant to hydrogen fuel technology.

A polymer is a large molecule made of many repeating smaller units called monomers, linked together in long chains. Polymers can be natural or synthetic. Natural polymers include DNA, proteins, cellulose (in plant cell walls), and rubber. Synthetic polymers include plastics like polyethylene (plastic bags), PVC (pipes), nylon (clothing), and Teflon (non-stick pans). Understanding polymer vocabulary is useful for chemistry, materials science, and environmental discussions about plastic waste.

Distillation is a separation technique that uses differences in boiling points to purify or separate liquid mixtures. A mixture is heated until one component vaporises; the vapour is then cooled and collected as a liquid. Simple distillation separates a liquid from dissolved solids. Fractional distillation separates mixtures of liquids with different boiling points, such as the components of crude oil in oil refining or the separation of alcohol and water in the spirits industry.

Chemistry and science vocabulary frequently appears in IELTS Academic reading and listening passages about environmental processes, industrial manufacturing, medical research, and food science. Cambridge exams at B2 and C1 levels include texts on topics such as water purification, climate chemistry, and pharmaceutical development. Key terms like catalyst, compound, reaction, solution, and pH appear across many scientific reading texts.