Atom

• An element in periodic table is made up of one type of atom - an atom is made up of three types of particles:

  • Protons
  • Electrons
  • Neutrons
• PROTON

  • Located in nucleus (centre of the atom)
  • Positive charge (+1)
  • Has a mass of 1 atomic mass unit (amu)
• ELECTRON

  • Found orbiting the nucleus in shells
  • Negative charge (-1)
  • Hardly have any mass - almost zero / negligible
• NEUTRON

  • Located in nucleus (centre of the atom)
  • Neutral charge (0)
  • Has a mass of 1 atomic mass unit (amu)
• • The number of protons (+) and electrons (-) are always equal in an atom - so atoms have no overall charge.
• Symbol of an atom of an element is shown with two numbers:

  
• Atomic number

  • Number of protons in the atom - also number of electrons in the shells around the nucleus (always the same number as protons).
• Mass number

  • Total number of protons and neutrons.
  • Number of neutrons = mass number - atomic number