The Early Periodic Table
John Newlands - 1864 - Arranged all the known elements into order of relative atomic mass - He found a pattern - He put the similar elements into vertical columns (groups)
Newlands pattern showed a repeating or periodic pattern of properties. By ordering by atomic mass he was forced to put some elements into groups which didnt match their chemical properties so his table was not accpepted.
Mendeleevs periodic table
Arranged elements known at time in order of relative atomic mass - Realised elements properties where related to atomic mass - Arranged them so that groups of elements with similar properties fell into vertical columns
Sometimes with this method there were gaps in his horizontal rows or 'periods' but these were empty for elements that hadnt yet been discovered. He was able to work out the atomic mass of missing elements and predict their properties.
The Modern Periodic Table
- Mendeleevs periodic table had some problems. However the discovery of protons, neutrons and electrons allowed mendeleevs table to be refined into the modern periodic table.
- The main modification was the use of the atomic number to order the elements. - Which is the number of protons it has.
- Using atomic number instead of atomic mass was proposed by Henry Mosley
Columns (Groups) : 1 - 7. Noble gases in group 0. All elements in a group have similar chemical properties because they all have the same number of electrons on their outer shell. The elements group number is the same as the number of electrons in their outer shell.
Rows (Periods) : Same number of occupied energy levels. e.g. Magnesium is in row 3 - its atoms have 3 occupied energy levels.
METAL ATOMS ALWAYS LOSE ELECTRONS WHEN THEY REACT WITH NON-METALS
NON METALS ATOMS ALWAYS GAIN ELECTRONS WHEN THEY REACT WITH METALS
Group 1 Elements
Group 1 metals are the Alkali Metals
Common properties of Alkali Metals
- Very Reactive - must be stored in oil to be kept away from air and water
- Less dense than water - they float
- Their reactivity increases as they go down because its easier to get rid of one of the electrons as it becomes more shielded
- They react quickly with water producing hydroxides and hydrogen gas.
- In general
- Group 1 metal + water = Group 1 metal hydroxide + hydrogen
- e.g. Lithium + Water = Lithiumhydroxide + hydrogen
- ... 2Li + 2H2O = 2LiOH + H2
Reactions with Group 1 Elements
Lithium = Li Sodium = Na Potassium = K
Reactions with Oxygen -
- Lithium and oxygen = lithiumoxide
- 4Li + O_2 = 2Li_2O (red flame)
- 4Na + O_2 = 2Na_2O (orange flame)
- 4k + O_2 = 2K_2O (Lilac Flame
Group 1 metals react with non metals to form ionic compounds. In these reactions the metal atom loses its outer electron and becomes a metal ion with a charge of +1. The ionic compounds produced are white solids which form colourless solutions when dissolved.
The elements in the centre of the periodic table - between the groups 2 and 3.
All metals - Most commonly used ones e.g. iron, copper, silver and gold.
PROPERTIES OF TRANSITION ELEMENTS
- High melting points (except murcury)
- Low reactivity
- Strong and hard
- High density (would sink in water)
- Make coloured compounds
Many transition elements act as catalysts e.g. Iron is the catalyst used in the Haber Process.
Group 7 Elements
The Halogens. - All toxic - can be used to sterilise or used as antiseptics.
- They are non metals
- Low melting and boiling points
- They are brittle when solid
- Poor conductors of heat and electricity
- They have coloured vapours
- Their molecules are diatonic ( have 2 atoms e.g. Cl_2)
Colour - Halogens become darker as you go down
Reactivity - They become less reactive as you go down the groups
Reactions - React with metals to form ionic compounds. Gain one electron to form a charge of -1.