IGCSE Chemistry Section B (Chemistry of the Elements)

• Good conductors of electricity and heat
• Soft and easily cut
• Low melting and boiling points
• Low densities
• Shiny surfaces when cut but come quickly dull
• Burn in air or oxygen to form white solid oxides

2M + O2 = M2O

• They are typical non-metals with relatively low melting points and boiling points.

• The melting points and boiling of the Halogens increase steadily down
  

• This increase in melting/boiling points down Group 7 is due to the increasing weak electrical intermolecular attractive forces with increasing size of atom or molecule.Generally the more electrons in the molecule the greater the attractive force between molecules.

• They are all coloured non-metallic elements and the colour gets darker down Group 7

• They are all poor conductors of heat and electricity - typical of non-metals.

• When solid they are brittle and crumbly e.g. iodine. The density increases down Group 7.

• The size of the atom gets bigger down Group 7 as more inner electron shells are filled going down from one period to another.

• • When combined with other elements in simple compounds the name of the halogen element changes slightly from ...ine to ...ide.

  • Fluorine forms a fluoride (ion F^-), chlorine forms a chloride (ion Cl^-), bromine a bromide (ion Br^-) and iodine an iodide (ion I^-).

  • The other element at the start of the compound name e.g. hydrogen, sodium, potassium, magnesium, calcium, etc. remains unchanged.

  • So typical halogen compound names are,  potassium fluoride, hydrogen chloride, sodium chloride, calcium bromide, magnesium iodide etc.

• The elements all exist as X₂ or X-X, diatomic molecules where X represents the halogen atom.

Hydrogen peroxide decomposes very slowly to form water and oxygen.

The apparatus originally contains 100cm3 of air. This is pushed backwards and forwards over heated copper metal (Cu), which turns black as copper(II) oxide (CuO) is formed.

CaCO3 + 2HCL = CaCl2 + H2O + CO2

Used for making carbonated drinks "fizzy"

In fire extinguishers, preventing oxygen from reaching flame.

Acid rain due to CO2 reacting with rainwater forming carbonic acid.

Although most metals are usually electropositive in nature and lose electrons in a chemical reaction they do not react with the same vigour or speed. Metals display different reactions towards different substances. The greater the ease with which an element loses its electrons and acquires a positive charge, the greater is its reactivity. Further, the greater the number of shells and lesser the number of valence electrons, the greater is the reactivity of the metal. The activity series of metals, arranges all metals in order of their decreasing chemical activity. As we go down the activity series from potassium to gold the ease with which a metal loses electrons, and forms positive ions in solutions, decreases