Element

A part or aspect of something abstract, especially one that is essential or characteristic.

Trace Element

A chemical element present only in minute amounts in a particular sample or environment.

Compound

A thing that is composed of two or more separate elements; a mixture.

Chemical Reaction

A process that involves rearrangement of the molecular or ionic structure of a substance, as opposed to a change in physical form or a nuclear reaction.

Reactant

A substance that takes part in and undergoes change during a reaction.

Product

 Is a substance that is formed as the result of a chemical reaction. In a reaction, starting materials called reactants interact with each other.

Molecule

A group of atoms bonded together, representing the smallest fundamental unit of a chemical compound that can take part in a chemical reaction.

Macromolecule

A molecule containing a very large number of atoms, such as a protein, nucleic acid, or synthetic polymer.

Carbohydrate

Any of a large group of organic compounds occurring in foods and living tissues and including sugars, starch, and cellulose. They contain hydrogen and oxygen in the same ratio as water and typically can be broken down to release energy in the animal body.