Classification of Matter

• An element is a pure substance made of one kind of atom that cannot be broken down or changed by usual means, and there are currently about 118 known elements.
• An atom is the smallest unit of an element that may lose, share or gain electrons when bonding and is the source of nuclear energy when split (fission).
• A compound is two or more different elements that are chemically combined, atoms bond in a fixed ratio, and cannot be separated by physical means, but must be separated by chemical means, and has properties unlike the elements that make it up.
• A molecule is the smallest unit of a compound, two different kinds of chemically combined atoms.
• A diatomic molecule is a molecule formed by two identical atoms, many gases are diatomic (O2, H2, N2, F2, Cl2).
• A mixture is different types and amounts of matter that are physically combined, each type of matter retains its own properties, and can be either homogeneous (mixed evenly, are the same throughout) or heterogeneous (not mixed evenly).
• A pure substance is matter that cannot be physically separated and only has one substance, elements, atoms, compounds, molecules, diatomic molecules are pure substances.