Chemistry 3a

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  • Chemistry 3a
    • history of periodic table
      • Newlands, and then Mendeleev,  classified by  order of  atomic weights
        • incomplete
        • inappropriate group placing e.g. oxygen and iron
        • Mendeleev  left gaps for elements that  had not been discovered and predicted them.
        • Newtons = octaves but it left elements in wrong group
      •  similar properties in columns, known as groups.
      • similar properties occur at regular intervals.
    • the modern periodic table
      • based on electronic structure
        • group number = number of electrons in o.s
        • columns = group
        • rows = periods (increase in no of electrons from l to r.
    • Group 1 - the alkali metals
      • down = more reactive and lower melting and boiling points
        • distance is greater, so easier to lose O.S.E. AND there is more sheilding to prevent the attraction between n and O.S.E.
      • lithium, sodium, potassium, rubidium, caesium
      • one O.S. electron
        • form ionic compounds with non-metals               -keen to lose  have to lose, not share ( not covalent)          produce white compounds that dissolve in water to produce colourless solutions
        • reaction with water produces hydrogen gas  -react vigorously       -they float and move                -they form hydroxides that dissolve in water to give an alkali solution.
      • low density (first three float)
    • Group 7 - the halogens
      • react with metals to form ionic compounds in which the halide ion carries a charge of –1.
      • In Group 7, the further down the group an element is:    ? the less reactive the element         ? the higher its melting point and boiling point.
      • A more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt.
      • All are non-metals with coloured vapours
      • form ionic bonds with metals
    • Transition metals
      • more than one ion
      • colourful
      • good catalyst


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