Chemistry: The branch of science that considers the composition of matter and how this composition changes.
Element: A chemical substance with only one type of atom.
Atom: Smallest particle of an element that has the properties of that element.
Nucleus: The dense core of an atom composed of protons and neutrons.
Electron: A small, negatively charged particle that revolves around the nucleus of an atom.
Proton: A positively charged particle in an atomic nucleus.
Neutron: An electrically neutral subatomic particle.
Atomic number: Number of protons in an atom of an element.
Atomic weight: Number approximately equal to number of protons plus number of neutrons in an atom of an element.
Isotope: An atom that has the same number of protons as other atoms of an element but has a different number of neutrons.
Ionic bond: A chemical bond formed between two ions by transfer of electrons.
Covalent bond: Chemical bond formed by electron sharing between atoms.
Hydrogen bond: A weak chemical bond between a hydrogen atom and an atom of oxygen or nitrogen.
Molecule: A particle composed of two or more joined atoms.
Compound: A substance composed of two or more chemically bonded elements.
Molecular formula: An abbreviation for the number of atoms of each element in a compound.
Structural formula: A representation of the way atoms bond to form a molecule, using symbols for each element and lines to indicate chemical bonds.
Synthesis: Building large molecules from smaller ones that join.
Decomposition: The breakdown of molecules into simpler compounds.
Exchange reaction: A chemical reaction in which parts of two kinds of molecules trade positions.
Reversible reaction: Chemical reaction in which the end products can change back into the reactants.
Catalyst : A chemical that increases the rate of a chemical reaction but is not permanently altered by the reaction.
Electrolyte: A substance that ionizes in water solution.
Acid: A substance that ionizes in water to release hydrogen ions.
Base: Substance that ionizes in water to release hydroxide ions or other ions that combine with hydrogen ions. pH scale: The negative logarithm of the hydrogen ion concentration used to indicate the acidic or alkaline condition of a solution.
Organic: Carbon-containing molecules.
Inorganic: Chemical substances that lack carbon and hydrogen.
Solvent: The liquid portion of a solution in which a solute is dissolved.
Oxygen: Used in energy release from glucose molecules.
Carbon dioxide: Waste product that results from metabolism.
Salts: Provide ions important for metabolic processes.
Carbohydrate: An organic compound that contains carbon, hydrogen, and oxygen, in a 1:2:1 ratio.
Sugar: A short-chain carbohydrate.
Monosaccharide: A simple sugar, such as glucose or fructose.