Chemistry is a subject loaded with complex words and phrases. This might seem a little overwhelming. In fact, getting to grips with all the scientific vocabulary might be the thing that is putting you off opening your textbooks in the first place.

Luckily, with this handy guide to the most important general chemistry terms, you should start feeling more comfortable in no time. They are worth knowing not only for chemists themselves, or for the professors and engineers who use them. Rather, everyone should know these words and definitions, as they help to unlock that world of fizzing experiments, laboratories, and flaming reactions that is chemistry.

So, if you are studying for your GCSEs, or if you need a refresh before your A Level exams, take a look at this introductory chemistry dictionary and learn something!

If you reckon you know it all already, check out our other articles with everything you need to know about chemistry.

Fundamental Terms in Chemistry: The Small Stuff

Let’s start small. Chemistry, basically, is the study of atoms, elements, compounds, and molecules. These are four terms to get you going. But what do they mean? It’s an important question, as these four things (and the stuff of which they themselves are made) make up everything in the universe.

An element – iron, say, or oxygen – is a pure substance or something that you cannot break down into another substance. You can only break it down into atoms, or the smallest bits of the element that you can still recognise as this or that element. An element is only lots of the same atom.

How about molecules and compounds? These are slightly different.

  • Molecules, simply, are two (or more) atoms joined – or bonded – together. So, whilst an oxygen atom is not a molecule, if two oxygen atoms bond together, then that is a molecule (what we would call O²).
  • Compounds are molecules that have bonds between two different types of atom. In this case, if you add a carbon atom to O², you get CO². This is carbon dioxide, and this is a compound.

If you're interested, we've also published a piece on wicked chemistry facts. Check it out!

Even Smaller: Further Terms in Basic Chemistry

To understand how these atoms bond together, we need to go smaller still. As you may know from your chemistry lessons, atoms are made of particles, which either clump in the atom’s nucleus or spin around that nucleus. These particles have a charge that is either positive, neutral, or negative. The nucleus (the centre of the atom) holds the protons, which have a positive charge, and the neutrons, which are neutral. The negatively-charged electrons, meanwhile, orbit the nucleus.

These are key to understanding how molecules and compounds are made. Atoms bond with each other because of these electrons, and there are two types of bonds: ionic and covalent.

  • With covalent bonds, two atoms share a pair (or more than one pair) of electrons.
  • In ionic bonds, one atom donates an electron to another. When this happens, the donating atom becomes an ion: it becomes positively charged. Metals are those elements that like to lose electrons, forming bonds and developing positive charges.

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Beakers and test tubes sit upon a pair of books. Study for your chemistry exams!
Become a chemist; learn this essential chemistry terminology!

Chemistry’s Key Vocab: Chemical States and Compounds

Now we’ve covered the basic chemistry terms, let’s take a look at some words that you’ll hear flying around your chemistry department.

Molecules make up substances, which can be found in three different states. These you will probably have heard already, but it is important to remember that a substance can change its state due to heat and pressure.

  • Gases: These are substances with no fixed shape or definable volume.
  • Liquids: Substances that are fluid, with no fixed shape but with a definite volume.
  • Solids: These substances are more stable, with their molecules more tightly packed. They have a more fixed shape, and a definite volume.

Substances can be pure elements, compounds, or mixtures. In chemistry, a mixture is defined as a substance made of two or more elements combined, but not chemically bonded like a compound.

There are different types of compounds, some of which most basic chemistry courses will require you to know:

  • Hydrocarbons: these are organic compounds, which contain – as the term suggests – only hydrogen and carbon.
  • Polymers: large molecules – either naturally occurring or synthetic and produced in a lab – that are formed of lots of bonded smaller molecules (often hydrocarbons).
  • Salt: an ionic compound whose charge is neutralised. It combines ions with a positive charge with those of a negative one.

Finally, in this section, we have acids and alkalis. These are opposites. Acids contain hydrogen, donate protons and make positive ions in water. Alkalis produce negative ions in water. You’ll see this again below, but if you want something a little more in depth, try out our piece on the central concepts in chemistry.

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Salt - a chemical - on a spoon. Photo by Joanna Kosinska
Salt is a chemical compound that you need to know!

Essential Terminology for Chemical Processes and Reactions

For most GCSE chemistry courses, you will need to know some basic terms for chemical reactions – or you will never understand what happens in the laboratory or in an experiment!

Firstly, you need to know the three terms of a chemical reaction. These are…

  • The reactant: that substance which is present at the start of the reaction.
  • The catalyst: the substance that enables the reaction, but that isn’t changed by it.
  • The product: what you get at the end of the reaction. The amount of this substance is known as the

All reactions are either endothermic or exothermic, meaning they either take in energy or give it out.

In this table, you can find some important words for the main types of reaction you will be dealing with:

OxidationA reaction, usually involving oxygen, in which an electron is lost.
ReductionWhen electrons are added to an atom (the opposite of the above!)
DistillationWhen a mixture loses a liquid by evaporation and condensation.
Thermal DecompositionBreaking a compound into two or more substances by heating.
Titration If you know the concentration of a solution, you can use titration to determine the concentration of a different solution.

Read some fun chemistry facts here!

The Language of Chemistry: Measurements, and the Periodic Table

Understanding the textbook terms used in your chemistry course is not only about knowing the atomic structures of states of matter. You also need to know the ways in which a chemist might make a calculation or measure a given substance. This indispensable terminology will help in any chemistry class.

  • The Periodic Table. You’ll have noticed this in any chemistry lab you’ve seen. This is the table of the elements, arranged in order of atomic number. It was invented by a bloke called Mendeleev, about whom you can learn more in our piece on the most important chemists ever.
  • Atomic number. An atom’s number of protons – and therefore electrons, as they are equal.
  • Mass number. The number of protons plus the number of neutrons.
  • Transition element. Elements in groups three to twelve of the periodic table. Also known as transition metals.
  • Mole. The unit used to identify a given amount of a substance. A mole of any substance contains the same number of atoms as a mole of another substance.
  • Reactivity. How reactive a substance is in relation to another. If you put substances in order of relative reactivity, you get a reactivity series.
  • Alongside a reaction, you will probably need to write a chemical equation. This shows, in written form, what reactants are involved and what products are produced.

You will also need to know another scale, the pH scale. This is used to describe how acidic or alkali a substance is. It ranges from 0 to 14, with the most acidic having the lowest number and the most alkali having the highest. Neutral substances are pH7.

A Word on the Most Important Chemistry Equipment.

Any introduction to chemistry vocabulary would be lacking without a mention of the most important equipment any scientist might use in their labs. Chemistry is not only theoretical and analytical, but empirical and therefore practical too!

Check out more in our article on the basic chemistry kit.

A Bunsen burner. Picture by Geoffrey Whiteway
A Bunsen burner is a key term in your chemistry equipment glossary.
  • Bunsen burner. Using this will be one of the highlights of your high school chemistry experience. By plugging this into a gas tap, you will get heat and a flame for your chemistry experiments.
  • Tripod and gauze. Over a Bunsen burner can be placed a stand that can hold beakers to be filled with chemical elements and solutions.
  • Test tube. The iconic tool of chemical science, this is a slim tube in which you will keep and perform experiments on your solutions. A boiling tube is a larger variety of test tube, in which – you guessed it! – you can boil things.
  • Burettes are like test tubes but have measurements and are clamped – so that you can drip little bits of solution. They are used mainly for titrations.
  • This is used not only in chemistry, but biology and medicinal science too. A little squeezy plastic tube to transport liquids.

Remember that chemistry affects us every single day. Why not read up on some life-changing chemistry discoveries whilst you're here?

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