Chemical Periodicity

Periodicity is the repeating pattern of properties in elements.
1. This regularity allows elements to be placed in groups
  1. Each element has similar, though gradually varying, properties
    1. These properties are both chemical and physical
Electron structure
1. Electrons orbit the nucleus at certain fixed distances- SHELLS
  1. Each shell can hold up a certain number of electrons
    1. Shell 1- 2 Electrons
    2. Shell 4- 2 Electrons
    3. Shell 3- 8 Electrons
    4. Shell 2- 8 Electrons
    5. Electrons fill up the nearest shells first
    6. Number of electrons in the outer shell= group number
2. All chemical reactions are the result of changes in the outer shell of electrons
  1. All elements in a group have the same number of electrons in the outer shell
    1. Therefore elements in any group have similar characteristics
    2. However, as groups descends, more shells are added
      1. More shells means more distance from the positively charged nucleus
        Therefore it is harder to gain electrons but easier to lose them
GROUP 0- NOBLE GASES
1. Highly unreactive
  1. Do not form compounds
    1. Full outer shell of electrons
2. Colourless gases
3. Down the group they become
  1. Denser
  2. Gain a higher boiling point
4. USES
  1. Helium
    1. Airships
    2. Party balloons
  2. Neon
    1. Filling gas discharge tubes for neon signs
    2. Cryogenic refrigeration
  3. Argon
    1. Inside lightbulbs to stop filament oxidation
    2. Food packaging to stop rotting
  4. Krypton
    1. Lasers
    2. Killing Superman
  5. Xenon
    1. Flash camera bulbs
    2. Strobe lights
GROUP 1 ALKALI METALS
1. Relatively low density
  1. Potassium, Sodium and Lithium float on water
2. Shiny when first cut
  1. Tarnish rapidly upon oxidation
3. Soft- can be cut by a knife
4. Low melting points
5. Silvery metals
  1. Caesium is pale-gold colour
6. Very reactive- most reactive metal group
  1. Stored under oil or under Argon atmosphere
  2. They react with water to give Oxides
  3. They react with water to give Hydroxides AND Hydrogen
    1. These reactions are very vigorous
      1. Lithium fizzes around on the surface of the water and seems to dissolve
      2. Sodium fizzes around in a molten ball, appearing to dissolve
        This is because Sodium has a lower boiling point than Lithium AND the reaction is more exothermic
      3. Potassium fizzes around in a molten ball, igniting the Hydrogen from the reaction and producing a purple flame
    2. The presence of Hydroxide products can be shown using an indicator
      1. Hydroxides are alkaline, thus why the metals are also known as the 'alkali metals'
7. As the group descends...
  1. The metals become more reactive
    1. Become softer
      1. Increase in density
  2. The metals want to lose an electron to have a full outer shell
    1. The further they are from the protons, the easier they can lose the electron
      1. The more shells they have, the further they are from the protons.
        As they descend the group, the become MORE reactive
GROUP 7- THE HALOGENS
1. Halogens are reactive non-metals
  1. They are diatomic molecules
    1. They have poisonous vapours
2. Halogens and their properties
  1. Fluorine
    1. Pale yellow
    2. Highly toxic
    3. Very reactive
    4. GAS
  2. Chlorine, Cl2
    1. Pale green gas
    2. Dense
    3. Toxic
    4. GAS
  3. Bromine, Br2
    1. Dense
    2. Dark red
    3. LIQUID
    4. Gives off red/brown vapour
    5. Toxic and Corrosive
  4. Iodine
    1. Dark grey
    2. SOLID
    3. Sublimes to give a purple vapour
    4. Forms a brown solution in water and a purple one in Hexane
  5. Astatine is radioactive and very unstable
  6. They are ALL poor conductors of heat and electricity
3. On descending the group...
  1. They become less reactive
    1. They are trying to ATTRACT electrons, unlike the Alkali metals
      1. This means they want to be nearer the protons and the nucleus
        Therefore they want fewer shells between them and the nucleus
  2. Their colour becomes darker
  3. Their melting and boiling points INCREASE

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