Atoms & ions

• Everything whether it's living, non-living or even a cell itself is made up of lots of tiny particles which we call atoms
• A single cell probably contains more than 100 trillion atoms
• Atom


  Basic structure is a central nucleus surrounded by electrons which orbit around the nucleus in rings that we call shells
• Particles that make up the nucleus

  • Protons
  • Neutrons
• Protons and neutrons


  • Have the same mass, with a relative mass of 1
  • Protons have a positive charge of 1+
  • Neutrons have no charge (are neutral)
• Electrons


  • Have a mass 2000 times smaller than protons and neutrons
  • Have a negative charge of 1-
• The size of an atom depends on which element it is
• Atoms have a radius of around 0.1 nanometers
• Most of an atom is actually empty space
• The nucleus is 10,000 times smaller than the width of the atom
• The electrons are even smaller than the nucleus and would be too small to see in the atom diagram
• Ion


  An atom that has lost or gained electrons, so the positive and negative charges no longer balance
• Ions


  • One minus negative ion (one extra electron)
  • Two minus negative ion (two extra electrons)
  • One plus positive ion (one less electron)
• The periodic table represents different types of atoms, which we call elements
• Atomic number


  Tells us how many protons the atoms of that element have
• Mass number


  Tells us the total number of neutrons and protons in that atom
• The number of protons and electrons in an atom is always the same