Chemistry C4

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Atomic Structure


  • The nucleus of an atom is made up of protons and neutrons
  • Electron : Relative charge = -1. Relative mass = 0
  • Proton : Relative charge = +1. Relative mass = 1
  • Neutron: Relative charge = 0. Relative mass = 1
  • An atom is neutral because it has an equal number of electrons and protons. The positive charges balance out the nagative charges


  • Elements with the same atomic number but different mass numbers are isotopes
  • The different numbers of neutrons is isotopes can be deduced

Arrangement of electrons in Atoms

  • The elements in the periodic table are arranged in order of increasing atomic number : an element with an electronic structure of 2.8.6 has three electron shells, so is in the third row
  • Elements in the same group (with the same number of electrons in the outer shell) are arranged vertically
  • Elements in the same period (in order of how many shells the electrons occupy) are arranged horizontally

The Development of Atomic Theory

  • An early theory of atoms was developed by John Dalton. His explanation was provisional.
  • JJ Thompson, Rutherford and Bohr found new evidence, their explanations changed the model of the atom

Ionic Bonding

Why do atoms form Bonds?

  • Atoms with an outer shell of eight electrons have a stable elctronic structure
  • Atoms can be made stable by transferring electrons. This is called ionic bonding
  • Metal atoms lose electrons to get a stable electronic structure
  • If an atom loses electrons, as


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