Atoms

• Atoms are the basic building blocks of all materials.
• An element is a substance made up of only one type of atom.
• A molecule is formed when two or more atoms join (bond) together chemically.
• Compound : When a molecule is made up of two or more different types of elements chemically combined, we call it a compound.
• All compounds are non-elements.
• The atom is made up of smaller particles called sub-atomic particles.These are:

  • Protons

  Neutrons

  • Electrons.
• Neutrons = 0

  protons = +1.

  Electron = -1
• • The atomic number tells you how many protons + electrons.
  • When you take the mass number away from the atomic number you’ll get the neutrons
• Atomic and mass number of lithium

  
• Electrons whizz around the nucleus in energy

  levels called shells, or orbits. The first shell can

  hold only two electrons; the second and third shells

  can each hold up to eight electrons.