The atom

• Protons and neutrons are in the nucleus
• electrons are on the outer shell which orbits the nucleus
• the number of protons are equal to the atomic number
• Protons relative mass is 1 and its charge is +1
• Neutron has a relative mass of 1 and a charge of 0
• Electrons have a relative mass of 1/2000 and a charge of -1
• The total number of electrons, protons and neutrons is called the mass number
• Isotopes are atoms with different numbers of neutrons but same amount of protons
• Atoms can gain or lose electrons to form ions
• Mass number – the big number 
• The size of an atom is about 10-10 meters or 10-8 centimeters. 
• To work out number of neutrons 

  Neutrons = mass number – atomic number 
• Relative Atomic Number (R.A.M)
• An atom is mostly neutral so it needs the same amount of positive and negative charge 
• Electronic Configuration is the amount of electrons on the outer shell
• Relative Formula Mass – Mr (relative mass) 

  R.A.M = Ar (Relative atomic mass) 
• CO2 

  Ar (C) = 12.0, Ar(O)-16.0 

  Mr(12.0X1)+(16.0X2) 

  =44 
• Empirical Formula – this is the simplest whole number ratio of the atoms of each element in a compound 
• C2H4 

  2 carbon 4 hydrogen 

  For every 1 Carbon, there are two Hydrogen atoms 

  CH2 
• Electrons is the relative atomic mass subtract by the atomic number