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Until recently there were two ways of categorising elements:
1) There physical and chemical properties
2) Their relative atomic mass
· 1864, John Newlands tried to arrange the elements using the law of octaves.
· His work was ignored as there was inconsistency as he progressed.
· In 1869, Dmitri Mendeelev expanded on Newlands' law of octaves.
· He left gaps and predicted new elements by ordering them by atomic mass.
· The modern periodic table is based on electronic structure.
· Elements in the same group have similar properties.
· This is because their atoms have the same number of electrons in the outer shell.
· Because of this pattern, we know that:
· 1) The larger atoms lose electrons more easily.
· The larger atoms gain electrons less easily.
Reactivity increases as you go down the group
As the atom gets bigger, the single electron in the outer shell shell is attracted less strongly by the
positive nucleus. This is because it is further away from the nucleus and the inner shells of electrons
screen it from the positive charge on the nucleus.
The outer electron is lost more easily, so as elements go down they become more reactive.
· They are all silvery solids
· There hydroxides dissolve in water to give alkaline solutions.
· As you go down the group the alkali metals become
1) Bigger atoms
2) More reactive
3) More Denser
4) Lower melting point
5) Lower boiling point.
· The alkali metals are all very reactive
· They all have one electron in their outer shell
· They are all keen to lose their one extra electron to form a 1+ ion
· They always make ionic compounds
Reactions with water always produce hydrogen gas.
· As you go down the metals you become:
· Less Reactive
· Higher melting point
· Higher boiling point
· They are all nonmetals with coloured vapours:
Fluorine: very reactive(poisonous yellow gas)
Chlorine: fairly reactive (poisonous green gas)
Bromine:Dense (poisonous red/brown gas)
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Iodine: Dark grey Crystalline solid or purple vapour.
· They all go around in pairs , e.g. : F2.
· They form 1 ions when they bond with metals.
· They react to form slats.
· Most reactive halogens will displace less reactive ones.
Reactivity decreases as you go down the group.
As the atoms get bigger an electron added to the outer shell is attracted less strongly to the positive