C2 Topic 4: Groups in the periodic table

Chemical classification

Metal structure
The structure of metals is a regular arrangement of positive metal ions surrounded by a sea of delocalised electrons.
Properties of metals
Good conductors of electricity
·  Delocalised electrons are free to move around randomly.
·  If a voltage is applied across a metal the electrons move to one direction.
·  This movement is an electric current
Malleable – bent into shape
·  Metal ions in a regular arrangement of layers
·  If a force is applied the layers can slide past each other and the metal bends.
·  The metal does not break as the ions are held together by the sea of electrons.
Ductile – drawn into wires
Shiny
Good conductors of heat / Transition metals

Most metals are transition metals.
·  They have very high melting and boiling points
·  They form coloured compounds.
Alkali metals
Group 1 elements:
·  They have 1 outer shell electron
·  They lose 1 electron to gain a full outer shell
·  Form cations with a +1 charge.
Alkali metals are solid at room temperature
Alkali metals are soft for metals
Alkali metals have low melting and boiling points for metals.
Alkali metals react vigorously with water
The products are a metal hydroxide & hydrogen
e.g. lithium + water à lithium hydroxide + hydrogen
2Li (s) + 2H2O (l) à 2LiOH (aq) + H2 (g)
e.g. sodium + water à sodium hydroxide + hydrogen
2Na (s) + 2H2O (l) à 2NaOH (aq) + H2 (g)
e.g. potassium + water à potassium hydroxide + hydrogen
2K (s) + 2H2O (l) à 2KOH (aq) + H2 (g)
Alkali metal / Reaction with water
Lithium / Fizzing – H2 given off
Floats on water
Metal disappears as it has reacted
Sodium / More fizzing than lithium
Floats on water
Heat given off
Molten ball of sodium formed which eventually disappears.
Orange flame seen
Potassium / Very vigorous reaction
Heat given off
Lilac flame seen
Reactivity increases as you move down group 1.
Explaining group 1 reactivity
·  The elements at the bottom of group 1 have more electrons than the elements at the top of the group
·  They have more electron shells
·  The electron in the outer shell is further from the nucleus
·  The attraction between positive and negative charges (i.e between the nucleus and the outer electron) is weaker when charges are further apart
·  So further down the group the outer electron is easier to lose and the elements react more readily.
Halogens
Group 7 elements
·  Have 7 outer shell electrons
·  They gain 1 electron to have a full outer shell
·  Form anions with -1 charge
Halogen / Colour / State
Fluorine / Pale yellow / Gas
Chlorine / Pale green / Gas
Bromine / Brown/red / Liquid
Iodine / Grey / Solid
Reactivity of halogens:
Reactivity increases as you go up group 7 i.e. fluorine is the most reactive.
·  This is because halogens react by gaining an electron
·  This is easier with fewer electron shells (because outer electrons are closer to the nucleus)
·  So fluorine is the most reactive halogen
Halogen reactions
Reactions with metals:
All halogens react with metals to form metal halides.
e.g. potassium + chlorine à potassium chloride
2K (s) +Cl2 (l) à 2KCl (s)
Reactions with hydrogen:
All halogens react with hydrogen gas to form hydrogen halides:
e.g. hydrogen + chlorine à hydrogen chloride
H2 (g) + Cl2 (g) à 2HCl(g) / Displacement reactions of halogens
Displacement reaction = a more reactive element displaces a less reactive element in a compound.
Displacement reactions can be used to prove the reactivity of the halogens.
Results table for displacement reactions:

Fluorine displaces chloride, bromide and iodide from their compounds and so is more reactive than all three.
Chlorine displaces bromide and iodide from their compounds, but cannot displace fluoride. Chlorine is therefore more reactive than bromine iodine but less reactive than fluorine.
Bromine displaces iodide from its compound but does not displace fluoride or chloride. Bromine is therefore more reactive than iodine but less reactive than fluorine and chlorine.
Iodine did not displace any halide from its compound and so is the least reactive of the four tested.
Order of reactivity:
Fluorine > Chlorine > Bromine > Iodine.
Noble gases
Group 0
·  Have full outer shells, very stable
·  Gases at room temperature
·  BP increases down the group
Discovery:
·  Chemists noticed that the density of pure nitrogen was less than the density of nitrogen extracted from the air
·  It was hypothesised that the nitrogen from air also contained a denser gas
·  Experiments were done to find the identity of this dense gas – it turned out to be argon
Uses:
Noble gas / Use / Why
Helium / Balloons & airships / Low density
Argon / Light-bulbs
Welding shield / Unreactive
Neon / Signs / Fluorescent