Chemistry Unit 3

• The elements are in order of atomic number
• Elements with the same porperties are sorted into groups

John Newlands (1864)

• He only knew of the existence of 63 elements
• He arranged them in order of relative atomic mass
• He found similar properties amongst every eighth element in the seris

Dimitri Mendeleev (1869)

• He left gaps to accomidate new discoveries

Modern table

• Now a useful tool

The Alkali Metals

• Very reactive with oxygen and water
• Include: Lithium, Sodium and Potassium
• Whe they react with non-metals they form ionic compounds
• In water they form a metal hydroxide and hydrogen gas
• They dissolve in water to form an alkali solution
• Potassium reacts so aggressively it sets on fire
• They get more reactive the lower down the group 

The Halogens

• There are five non-metals in the Group
• Chlorine is the most reactive element in Group 7
• A more reactive halogen will displace a less reactive one