Chemistry

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  • Created by: Chesca
  • Created on: 15-05-13 15:12

Periodic Table

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)

 

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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
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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 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)

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Transition elements

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!

 

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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

 

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