John Dalton = arranged in order of atomic mass (1808)
John Newland = 'law of octaves' - order of atomic mass
- 1864. Left no gaps, elements with different properties in same group. Every 8th element properties similar
Mendeleev = order of atomic weight
- Left gaps for undiscovered elements
- Made predictions
- Arranged in periods
- (Not all fitted correctly argon with sodium)
Modern Periodic table
Arraged in order of atomic (proton) number!!
- elements in groups = similar properties
Group number= number of electron in outer shell.
Go down group...atoms get bigger:
- lose electrons easier/ gain electrons harder
- More reactive = away from attractive force of nucleus
- Further away from nucleus 'shielded' by other electrons
Group 1- Alkali metals
Lithium, Sodium, Potassium, Rubidium, Caesium, Frankium
Reactive: (one electron in outer shell) (going down = more)
- Stored in oil to prevent reacting with oxygen
Low melting / boiling point (decrease down the group)
React with non-metals (chlorine) form 1+ charge (ionic compounds) (form metal chlorides - white solids)
React with water - Li, Na, K, fizz and form hydrogen gas (produces hydroxides) - (soluable in water)
Good conductors of electricity and energy
Hard + Strong
High melting points (exception = mercury)
Less reactive than Group 1 elements (don't react easily with oxygen and water) corrode slowly!
Form coloured compounds (copper sulfate = blue)
Can form more than 1 ion (Iron 11, Iron 111)
Used as catalysts!
The Halogens - Group 7
(F, CI, Br, I, At)
Non-metals - form coloured vapours!
Low melting + boiling point
Poor conductors of energy and electricity
Molecules made of pairs of atoms
7 electrons in outer shell - gain 1 electron to get stable
- take part in ionic and covalent bonding (form 1- charge)
Reactivity decreases as you go down...
Reactive halogens, displace less reactive halogens