C1.1 fundamental ideas

The smallest unit of any chemical

Chemical that has only one type of atom

e.g. Na, C, O2, H2

Different atoms joined (chemically bonded)

e.g. H2O, NaCl, C2H6

elements and or compounds NOT joined

e.g. air, NaCl solution

Protons and neutrons make up the nucleus of an atom.  Protons have a charge of +1 and neutrons have a charge of 0.

          particle                 relative mass                  charge

           proton                           1                               +1 

          neutron                          1                                0

          electron                    almost 0                          -1

= the number of protons

(= the number of electrons in an atom)

= the number of protons + neutrons

Electrons are arranged in shells or main energy levels.

They are filled from the inner shell first.  This is the 1st shell and it has the lowest energy level.

Each shell can contain a maximum number of shells..

1st shell = 2 electrons, 2nd shell = 8 electrons, 3rd shell = 8 electrons etc

This is a table of elements.

It is arranged in:

periods: the rows - which correspond to a shell being fllled

groups: the columns - each group has the same number of electrons on the outer shell

e.g. Li = 2,1

     Na = 2,8,1

       K = 2,8,8,1

The arrangement of electrons can also be written using the number of electrons for each shell.

e.g. Chlorine  2,  8,  7  <-- (number of electrons in each shell)

        Shell:    1st   2nd  3rd

The number of electrons that are on the outer shell is the group that it is in, so chlorine would be in group 7 as it has 7 electrons in the outer shell.