Chemistry C4,C5,C6 notes

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  • Created by: flo
  • Created on: 13-06-13 11:14


Ionic bonding:
•Ionic bonds form between ionic compounds (metal and non-metal). 
•Metal loses electrons, non-metal gains them, so they attract. 
•ions in ionic compounds are arranged in a regular way. 'Giant (repeated) Ionic lattice', gives strong bonds as positive and negative ions are strongly attracted. 
•A lot of energy is needed to break ionic bonds, which is why they have high melting points. 
•Ionic compounds can't conduct electricity when solid, as their electrons can't move about, but they can when molten or in solution. 

Periodic table:
•The period is the number of shells or numbers in the electronic structure. 
•The group is the last number. 
(Periods go across)

Covalent bonding:
•Non-metals combine with each other to form covalent compounds, these have covalent bonds-a shared pair of electrons. 
• A molecule is a particle containing two or more atoms chemically bided together. E.g H2O or CO2
•Covalent bonds between atoms in a molecule=strong. 
•The intermolecular forces between molecules=weak. Little energy is needed to overcome them, which is why water and carbon dioxide have low melting points. 

Group one elements:
•All metals
•React vigorously with water to produce an alkaline solution, and so are called alkali metals. 
•Li, Na, K=so reactive with water and air (water vapour) that they are stored under oil. 
•Metal + water---> metal hydroxide + hydrogen. 
• 2M + 2H2O--->2MOH +H2
(M=metal symbol)
• OIL. Oxidation happens in group 1. M - e- ---> M+
• When reacting with water the H causes fizzing, pushing the metal around the surface. 
•Potassium ignites and burns with a lilac flame. 
•The reactivity increases as you go down the group because they all have 1 electron in their outer shell (this is why they have similar chemical properties) and it becomes easier to lose as there is less attraction from the positive nucleus the further down the periods you go (more shells). 
•Melting points decrease and densities increase the further down you go. 

Flame tests:
• Very high temperatures cause metal ions in metal compounds to vaporise. 
•They absorb the heat energy, causing their electrons to jump into higher shells, when the electrons drop back into their normal shells, light energy is released. 
•Flame tests identify different metal ions. 
•Na= orange (street lamps)
•K= Lilac (same flame in water)

Group seven elements:
•Halogens ('salt formers')- they react with metals to produce salts. 
•Chlorine- sterilise tap water and swimming pools, killing harmful bacteria making the water safe. 
•Chlorine- also used to make pesticides and plastics (PVC). 
•Iodine- used as an antiseptic. 
•Group 7 elements have similar properties because their outer shells contain 7 electrons. 
At room temperature......
•Chlorine---> green gas
•Bromine---> Orange Liquid
•Iodine---> grey solid (turns easily into a purple vapour when warmed).
•Group 1 + Group 7 ---> (clouds of) metal halide. 
• 2M + X2 ---> 2MX
(M=Group 1 element, X=Group 7 element). 
•Melting point increases as you go down the group. 
•Reactivity decreases as you go down the group!

Displacement Reactions:
•Group 7 + Metal Halide


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