The Chemistry Lexicon

Decode any chemistry term. Understand the language of molecules through etymology, examples, and expert insights.

Chemistry has a language problem. Before you can even understand a reaction, you have to decode the words first. Why does -lysis mean breaking down, but -osis means a state or condition? Why do molarity and molality look almost the same but behave completely differently inside a formula?

I built ChemLexicon to answer those questions. Every term page breaks the word into its parts, explains where it comes from, and shows you how to use it. Every confused pair gets a side-by-side comparison. No forming big grammar for nothing. Just clear explanations from someone who has taught this subject and watched students struggle with the same terms year after year.

Browse Terms

Roots, prefixes, and suffixes that form the language of chemistry.

-lysis

Decomposition or breaking down

hydro-

Water

-osis

Condition, state, or abnormal process

iso-

Equal, same, or uniform

therm-

Heat or temperature

-genesis

Origin, formation, or creation

Commonly Confused Pairs

The chemistry terms students mix up the most, explained clearly.

Molarity vs Molality

Molarity is moles of solute per litre of solution. Molality is moles of solute per kilogram of solvent.

Heat vs Temperature

Heat is energy in transit between bodies at different temperatures. Temperature is the average kinetic energy of the particles in a body.

Strong Acid vs Concentrated Acid

Strong means the acid ionises completely in water. Concentrated means there is a large amount of acid relative to the water.

Molecule vs Compound

A molecule is any two or more atoms bonded together. A compound is a molecule made of different elements.

Oxidation vs Reduction

Oxidation is loss of electrons. Reduction is gain of electrons.

Exothermic vs Endothermic

Exothermic releases heat to the surroundings. Endothermic absorbs heat from the surroundings.

Covalent vs Ionic Bond

A covalent bond is sharing of electrons between atoms. An ionic bond is transfer of electrons followed by electrostatic attraction.

Evaporation vs Boiling

Evaporation happens at the surface at any temperature. Boiling happens throughout the liquid at a specific temperature.

Atom vs Ion

An atom is electrically neutral. An ion is an atom that has gained or lost electrons and carries a charge.

Element vs Compound

An element contains only one type of atom. A compound contains two or more different elements chemically bonded in a fixed ratio.

Intermediate vs Transition State

An intermediate is a real molecule that sits in a valley on the energy diagram. A transition state is just a moment at the top of the hump, and you can never isolate it.

Concentration vs Activity

Concentration is the literal amount of solute you put in. Activity is the effective concentration the ions actually behave like.

Enantiomer vs Diastereomer

Enantiomers are mirror images that you cannot superimpose. Diastereomers are stereoisomers that are not mirror images at all.

Qualitative vs Quantitative

Qualitative is about what something is. Quantitative is about how much of it there is.

Isomer vs Conformer

Isomers need bonds to break before they can change into each other. Conformers just rotate around single bonds.

Melting vs Dissolving

Melting is a solid turning into a liquid because of heat. Dissolving is a solid mixing into a liquid solvent without changing what it is.

Equivalence Point vs End Point

The equivalence point is the theoretical moment when acid and base have reacted exactly. The end point is when the indicator actually changes colour.

Basicity vs Nucleophilicity

Basicity is how strongly a species grabs a proton. Nucleophilicity is how fast it attacks a carbon atom.

Adsorption vs Absorption

Adsorption is when molecules stick to the surface of a material. Absorption is when molecules go inside and spread throughout the material.

Hermetic Seal vs Cohesive Seal

A hermetic seal is a complete airtight barrier that nothing can pass through. A cohesive seal just holds two surfaces together with something sticky.

Promethium vs Plutonium

Promethium is a rare-earth lanthanide with mild radioactivity. Plutonium is a heavy actinide that can sustain nuclear fission.

Intensive vs Extensive Properties

Intensive properties do not depend on how much substance you have. Extensive properties do.

Homogeneous vs Heterogeneous Catalysis

In homogeneous catalysis, the catalyst is in the same phase as the reactants. In heterogeneous catalysis, it is in a different phase.

Coordination Number vs Oxidation State

Coordination number is the count of bonds to the metal. Oxidation state is the theoretical charge on the metal.

About ChemLexicon

ChemLexicon is written by Beatrice Ojuederie, a graduate scientist with a degree in Pharmacy. It exists to help students, teachers, and anybody learning chemistry decode the language of the subject without the usual confusion.