The modern periodic table

The modern periodic table

1. For many years, an elements atomic number was just its position on the periodic table

   • Then in 1931, we worked out that the elements atomic number was the number of protons in its atoms = also number of electrons which surround the atom in its energy levels

2. The total number of protons and neutrons in the nucleus of an atom is called its mass number

3. Top no. = mass number

   • Bottom no. = atomic number

4. Mass number is always bigger- you take away atomic number from mass number to get neutrons

   • Relative atomic mass- The mass of an atom is incredibly small so we use relative atomic mass instead f iys actual mass in KG
     • The symbol for atomic mass is Ar
       • Carbon is used as the standard atom
         • carbon -12 atom has 6 of every subatomic particale
           • The masses of all other atoms are compared to this
             • for example the mass of a helium-4 atom is one third of a carbon 12 atom. So its relative atomic mass is 4

5. The modern periodic table-

   • elements in the periodic table go in the order of increasing atomic number rather than atomic mass as M did.
     • horizontal rows are called periods-Vertical columns are called groups
       • Each group contains elements with similar properties