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How to Understand Atoms

The structure of atoms determines their physical and chemical properties. Using these guidelines, you can understand why some atoms are reactive and others are not.


  • Step 1: Consider atomic number Consider the atom's atomic number. This is the number of protons in the atom's nucleus.
  • TIP: The nucleus of an atom contains protons and neutrons. It is surrounded by electrons.
  • Step 2: Consider atomic mass number Consider the atom's atomic mass number. This is the number of protons and neutrons in the nucleus.
  • Step 3: Consider electronic configuration Consider the atom's electronic configuration. The electrons in an atom have fixed orbits with discrete energy levels. Atoms whose outer energy levels are full are less reactive than those with unfilled energy levels.
  • FACT: The theory of atomic structure was developed in the early 20th century.

You Will Need

  • Atom
  • Atomic number
  • Atomic mass number
  • Electronic configuration
  • Protons (optional)
  • Neutrons (optional)
  • Electrons (optional)

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