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.