Summary of Atoms, Elements, Compounds, and Molecules

  • Atoms

    • Basic unit of matter, smallest form of an element.

  • Elements

    • Pure substances made up of only one type of atom.

  • Molecules

    • Composed of two or more atoms joined together by a chemical bond; can be the same or different atoms.

  • Compounds

    • Two or more different types of atoms joined together by a chemical bond.

  • Pure Substances

    • Cannot be separated into parts without breaking a chemical bond.

  • Differences to Note:

    • Elements are made of one type of atom, while molecules can be made of the same or different atoms.
    • Compounds specifically refer to different atoms bonded together, unlike molecules which can include the same atom.

  • Atomic Number & Mass Number

    • Atomic number refers to the number of protons, which determines the element’s identity.
    • Mass number is the sum of protons and neutrons in the nucleus.

  • Water (H2O)

    • Is considered both a compound (different types of atoms) and a molecule (two types of atoms bonded together).

  • Understanding Chemical Properties

    • The number of protons affects an atom's chemical properties. Different types of bonds influence substance characteristics. Arrangements of atoms within molecules can change physical properties.