structure and bonding

• Bohr model

  Protons and neutrons are found in the centre of the atom called the nucleus. (Protons and neutrons can also be called nucleons)

  Electrons orbit around the nucleus in shells or energy levels.
• Atomic number

  Number of protons in a nucleus
• Mass number

  Number(sum) of protons and neutrons in a nucleus
• Positive Ions (cations) – An atom has lost electrons so that there are more protons than electrons.
• Negative Ions (anions) – An atom has gained electrons so that there are more electrons than protons.
• Isotopes - are atoms with the same number of protons but a different number of neutrons.
• Compounds are made from more than one type of atom bonded together. Atoms bond together so that they gain a full outer shell of electrons and so become more stable.
• An ionic bond forms between metals and non-metals.

  • Electrons are always transferred from the metal to the non-metal.
  • The metal will therefore always form a positive ion, and the non-metal will form a negative ion.
  • An ionic bond is the strong electrostatic attraction between oppositely charged ions.