Atoms

• all substances are made up of atoms
• nucleus of an atom contains protons and neutrons
• the nucleus has a positive charge
• electrons 


  relative mass = 1/2000

  charge = -1
• proton 


  relative mass = 1

  charge = +1
• atomic number is the number of protons in the nucleus
• mass number is the total number of protons and neutrons in the nucleus
• neutron 


  relative mass = 1

  charge = 0
• electrons


  move around the nucleus in electron shells
• atoms are neutral in charge
• in an atom the number of protons = number of electrons
• ion


  an atom that has lost or gained electrons
• the number of protons decides what kind of atom it is
• isotopes 


  an atom that has the same number of protons but a different number of neutrons
• isotopes have the same atomic number but different mass number
• relative atomic mass = sum of isotopic mass / sum of atomic mass
• atoms join together to make compounds
• compounds are held together by chemical bonds
• ionic bonding 


  a compound made with a metal and non-metal
• carbon dioxide - CO2
• sodium chloride - NaCl
• ammonia - NH3
• Water - H2O
• Carbon monoxide - CO
• hydrochloric acid - HCl
• calcium chloride - CaCl
• sodium carbonate - Na2CO3
• sulfuric acid - H2SO4