Topic 6 - Groups in the Periodic Table

• One outer electron.
• Similar chemical properties. 
• Have low melting and boiling points, also very soft.
• Form ionic compounds but dont form covelent bonds.
• Form a 1+ ion when they lose their outer electron.
• Reactivity increases going down the group because the electron becomes furhter away from the nucleus and has a weaker attraction.
• React vigerously in water.
• Produce hydrogen and hyudroxide of the metal.

Reactions get violent as you go down the group:

• Lithium: fizzes furiously whist moving around the surface.
• Sodium and potassium: do the same but also melt, potassium ignites the hydrogen it produces.

• 7 outer electrons. 
• Exsist as diatomic particles. Share one pair of electrons in a covalent bond. Gives both atomes a full outer shell.
• Melting and boiling points of halogens increase as you go down the group.

At room temperature:

• Chlorine: fairly reactive, poinonous, green gas. Test: hold a piece of damp blue litmus paper over chlorine, chlorine will bleach the paper. Is acidic.
• Bromine: poisonous,  red-brown liquid.
• Iodine: dark grey crystalline solid which gives off purple vapour when heated.
• Gains one electrom to form a 1- ion.
• Less reactive as you go down as its harder to attract the extra electron when the nucleus is further away.
• React vigerously to form salts called metal halides.
• Can react with hydrogen to form hydrogen halides which are soluble. Dissolve in water to form acidic solutions.

More reactive element will push out a less reactive one (group 7).

• Redox reactions. Halogens gain electrons whilst ions lose them.

• Example: Chlorine is more reactive than bromine, so if you add chlorine water to potassium bromine solution, chlorine displaces the bromine from the slat solution. Chlorine is reduced to chloride ions, salt solution becomes potassium chloride. Bromide ions oxidised to bromine, turns solution orange.

Displacement reaction showing trends of halogens:

• Measure out small amount of halide salt solution in test tube.
• Add few drops of halogen solution, shake tube gently.
• If colour changes, reaction has happened. Halogen has displaced halide ions from the salt. No reaction = no colour change as the halogen is less reactive than the halide.
• Repeat process using different combinations of halide salt and halogen.
• Chlorine water + potassium iodide = brown solution
• Bromine water + potassium iodide = brown solution

• Colourless gases at room temp.
• Monatomic - gases are made up of single atoms.
• Don't react with much (inert - non-flammable) as they have a full outer shell.
• Took a long time for them to be discovered.
• Can be used to provide an inert atmosphere like argon does in filament bulbs (stops filament burning away) 
• Argon, krypton and xenon used to stop the flash fimament from burning away.
• Argon and helium used to protects metals being welded. Inert atmosphere stops metal reacting with oxygen.
• Helium has a low density, so makes balloons float and can be useful in airships.
• Boiling and melting point and density increase as you go down the group.