The Alkali Metals and The Halogens

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Properties of The Alkali Metals?

The elements in group 1 are very unusual. They are metals but their properties are not typical of metals. 

  • They are very reactive 
  • They are very useful when contained in other compounds 
  • They have low melting points 
  • As you go down group 1 the metals get softer and become more reactive
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Reacting alkali metals with oxygen

When alkali metals are lefted in oxygen they go dull and tarnish. 

lithium + oxygen ---> lithium oxide 

LI        +   O2    ----->  Li2O

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Reacting alkali metals with water

when lithium is added to water it moves across the surface of the water and fizzes

lithium + water --> lithium hydroxide + hydrogen 

when sodium is added to water is moves and turns into a ball while fizzing and moving across the water 

sodium + water --> sodium hydroxide + hydrogen 

when potassium is added to water it turns into a ball and catches a liluc flame and starts to spit 

potassium + water --> potassium hyroxide + hydrogen

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Properties of The Halogens?

The halogen metals go round in pairs. They are called Diatomic Molecules

As you go down the group the elements turn from a gas to solid and also change from a pale yellow to a black grey. 

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Testing compounds?

Compounds like sodium chloride, potasium chloride and sodium iodide are salts. They are all made up of crystals 

The first name in the compound is the metal which has a positive ions and the second name of the compind is the non metal which has a negative ion. 

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Testing for Metal ions ( Flame Test )

  • Dip a piece of nichrome wire into a salt 
  • Place into the blue flame of the Bunsun Burner 
  • Look for a colour change in the flame 

Results

  • If the salt contained sodium the flame would turn orange/yellow 
  • If the salt contained lithium the flame would turn scarlet red
  • If the salt contained potassium the flame would turn lilac/pink
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Testing for Chloride Bromide and Iodide

  • Place a small spatula of salt into a test tube 
  • Add a pipette full of dilute nitric acid 
  • Shake the test tube to dissolve the salt 
  • Add a pipette full of silver nitate solution 

Results

If a white precipitate forms the solid is a chloride 

If a cream precipiate forms the solid is a bromide 

If a pale yellow precipitate forms the solid is a iodide

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