Chemistry

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)

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

Lithium, Sodium, Potassium, Rubidium, Caesium, Frankium

Reactive: (one electron in outer shell) (going down = more)

• Stored in oil to prevent reacting with oxygen

Low density

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 densities

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!

(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