Trends within the periodic table

1.2.2 Elements

2.1.1 Chemical reactions

Trends within the periodic table

  1. Group 0 - Noble gases

    1. Nobles gases have eight electrons in their highest energy level, except for helium, which has only two electrons
    2. They are unreactive because their atoms have stable arrangements of electrons

  2. Group I - Alkali metals

    1. They have low densities (the first three elements in the group are less dense than water)
    2. They react with non-metals to form ionic compounds in which the metal ion carries a charge of +1
    3. Their compounds are white solids that dissolve in water to form colourless solutions
    4. They form hydroxides that dissolve in water to form alkaline solutions
    5. They react with water, effervescing hydrogen, forming their hydroxide, reducing in size as they react away, the lighter ones floating on top and moving to the edge of the container, the more reactive ones burning with their characteristic flame colour or exploding
    6. The further down the group an element is, the more reactive the element is

  3. Transition metals

    1. Compared to Group I

      1. They have a higher melting point (except for Mercury)
      2. They have higher densities
      3. They are stronger and harder
      4. They are much less reactive so do not react as vigorously with water or oxygen
    2. Many transition metals form ions with different charges
    3. They form coloured compounds
    4. They are useful as catalysts

  4. Group VII - Halogens

    1. They react with metals to form ionic compounds in which the halide ion carries a charge of -1
    2. The further down the group an element is, the less reactive the element
    3. The further down the group an element is, the higher its melting & boiling point is
    4. A more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt

  5. Explanation of trends in reactivity within groups

    1. The higher the energy level of the valence electrons:

      1. the weaker the electrostatic force of the nucleus
      2. the stronger the shielding effect of the inner electrons
      3. the stronger the electrostatic repulsion of the other electrons
    2. Therefore, the higher the energy level of the valence electrons, the more easily electrons are lost and the less easily electrons are gained