Chemistry Glossary of Terms - Atoms, Compounds, and Ions

Chemistry is a science that explores the properties of matter. Simply put, it's the study of what the world is made of and how these different substances interact. Understanding chemistry can give us a much deeper understanding of the world around us, but learning about this subject will involve learning some new vocabulary. These terms help chemists to better describe the characteristics of and reactions between different atoms and compounds. 

Acid: A substance with a pH lower than 7 

Atom: The smallest possible unit of an element that has all of the properties of that element 

Avogadro's Number: The number of atoms, ions, or molecules of a substance in one mole of that substance. The value of this mathematical constant is 6.023 times 10 to the 23rd power. 

Balanced Equation: A chemical equation that is balanced, meaning that every atom on the left side of the equation is accounted for on the right side and vice versa 

Base: A substance with a pH higher than 7 

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Catalyst: Something that encourages a chemical reaction without being consumed in the reaction 

Chemical Bond: A bond between atoms or ions that allows molecules to form 

Chemical Equation: The equation that represents a chemical reaction 

Compound: A substance made from identical molecules that contain more than one element 

Corrosion: The deterioration of a metal through a chemical reaction with oxygen 

Covalent Bond: A bond between atoms created when they share electrons 

Electron: A negatively charged particle that orbits the nucleus of an atom 

Element: A substance that cannot be broken down into other substances 

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Group: One column of the periodic table. Elements in the same group have the same number of electrons in their outer shell. 

Ion: An electrically charged atom 

Ionic Bond: A bond between ions that have opposing charges 

Isotopes: Different versions of the same element, with each having a different number of neutrons but the same number of protons 

Metallic Bond: A chemical bond in which electrons float between atoms of metal, such as in a copper wire or aluminum foil 

Molar Mass: The average mass of one mole of a given chemical compound 

Mole: A standard unit of measurement in chemistry, defined as the amount of a substance that contains the same number of atoms, ions, or molecules as there are atoms in 0.012 kg of carbon 12. This number is a mathematical constant known as Avogadro's number. 

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Molecule: Two or more atoms that are chemically bonded. Molecules can contain multiple atoms of the same element or atoms of different elements. 

Neutron: A particle within the nucleus of an atom that has no charge 

Nucleus: The center of an atom, containing one or more protons and neutrons 

Period: A row of the periodic table, which contains the elements that successively fill up a specific electron shell with electrons. The first element in each period has one electron in its outer shell, making it relatively unstable, while the last element in each period has a full outer shell, making it relatively stable. 

pH: A measurement of how basic or acidic a liquid is. The pH scale goes from 0 to 14, with 7 being neutral. 

Product: The substance formed during a chemical reaction 

Proton: A positively charged particle in the nucleus of an atom 

Reactant: A material that is chemically changed in the course of a chemical reaction 

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Solute: Something that is dissolved in a solvent 

Solution: The mixture created when a solute is dissolved in a solvent 

Solvent: A substance, usually a liquid, that can dissolve another substance to create a solution 

Stoichiometry: The study of chemical equations that focuses on how much of each reactant needs to be added to a reaction to get a certain amount of product at the end 

Valence Electron: An electron in the outer shell of an atom that is free to become part of a chemical bond 

Additional Resources 

• The Mole and Avogadro's Number 
• Crash Course: pH and pOH 
• Periodic Table of Elements 
• Stoichiometry and the Mole 
• Compound Basics 
• What Is a Solution? 
• Atomic Bonding 
• What Are Isotopes? 
• Electron Structure of Atoms 
• Carbon Isotopes 
• Amadeo Avogadro Enumerated the Molecular World 
• How Do You Balance a Chemical Equation? 
• Iridium: The Most Corrosion-Resistant Metal 
• Four New Elements Added to the Periodic Table 
• Outer Space Molecule Chase 
• Seven Things You May Not Know About Catalysis