Substance
1. A substance is a pure form of matter, which means it has only one type of atom or molecule that can be classified into two parts.
2. A substance is matter which has a specific composition and specific properties.
Continuing along our flow chart, we see that pure substances can be further divided into two sub-categories: elements and compounds.
Elements are the simplest form of matter, which means they cannot be broken down into smaller components physically or chemically. All elements are listed on the periodic table, and there are at least 118 of them known to man. Examples of elements include carbon (C), hydrogen (H), oxygen (O), and sodium (Na), just to name a few.
Compounds, on the other hand, are made up of two or more different elements held together by chemical bonds and functioning as a unit. While compounds are also pure substances, they differ from elements because compounds can be broken down into simpler components (the elements that make up the compound). Some examples of compounds are carbon dioxide (CO2), rust (Fe2O3), and table salt (NaCl).
National Cancer Institute https://www.cancer.gov/publications/dictionaries/
Khan Academy https://www.khanacademy.org/science/physics/
Chemicool Dictionary https://www.chemicool.com/definition/