1.6 The periodic table

• what generally happens to IE across a period?

  increase, as increase in nuclear charge but shielding is similar
• what generally happens to IE down a group?

  decreases, outer electrons has increased shielding + distance from positive nuclear charge.
• what happens to electronegativity across a period?

  increases, increased nuclear charge but similar shielding
• what happens to mpt and bpt across elements?

  -increase from 1st to 4th element

  -large decrease to 5th element

  -small decrease to 8th element

  -bonding changes from metallic to giant covalent to simple molecular covalent
• what is an oxidising agent?

  species that accepts electrons, becomes reduced in the process
• what is a reducing agent?

  species that donates electrons, becomes oxidised in process
• how to tell if a species is oxidised or reduced?

  oxidation number increases = oxidised

  oxidation number decreases= reduced
• What happens when group 1 metals react with cold water?

  react vigorously to form hydroxide and hydrogen

  e.g. $2Na(s)\ +$$\ 2H_2O(l)\ \rightarrow\ 2NaOH\ (aq)+$$\ H_2(g)$
• What are the observations from each group 1 metal?

  Lithium = floats, fizzes + moves

  Sodium = floats, fizzes, moves + melts

  Potassium = floats, fizzes, moves, melts + burns with a lilac flame
• How does group 2 metals react with water?

  less vigorously, form a hydroxide + hydrogen
• what can be observed?

  magnesium = reacts slowly

  calcium = steady stream of bubbles + white precipitate of calcium hydroxide

  (reaction increases down group)

  e.g. $Ca\ (s)\ +$$2H_2O\ (l)\ \rightarrow\ Ca\left(OH\right)_2(s)\ +$$\ H_2$
• Why are group 1 metals more reactive than group 2 metals?

  lose only 1 electron while group 2 metals lose 2
• What happens when group 1 + 2 metals react with oxygen?

  all group 1 + 2 metals burn to form solid white oxides

  e.g. $4Li\ (s)+$$\ O_2(g)\ \rightarrow\ 2Li_2O\ (s)$
• What are all s-block metal oxides?

  -Strong bases + neutralise acids to form salt and water

  e.g.$MgO\ (s)\ +$$2HCl\ (aq)\ \rightarrow\ MgCl_2\ (s)+$$\ H_2O(l)$

  -Group 1 oxides + barium oxide react to form soluble hydroxide + alkali

  e.g. $Na_2O\ (s)\ +$$\ H_2O(l)\ \rightarrow\ 2NaOH\ (aq)$
• what colours do s-block elements give during a flame test?

  Li+ = red

  Na+ = organge/yellow

  K+ = lilac

  Ca2+ = brick red

  Sr2+ = crimson

  Ba2+ = apple green
• What group 1 + 2 metals are soluble in water?

  -all group 1 compounds are soluble

  -Many group 2 compounds are not

  group 2;

  -all nitrates are soluble

  -all carbonates are insoluble

  -hydroxides are more soluble as you go down the group

  Magnesium hydroxide is insoluble, Barium hydroxide is soluble.

  e.g. $Mg^{2+}(aq)\ +$$\ 2OH^-(aq)\ \rightarrow\ Mg\left(OH\right)_2(s)$
• What happens to sulfates down group 1?

  -Sulfates become less soluble as you go down group.

  -magnesium sulfate is soluble + barium sulfate is insoluble.

  e.g. $Ba^{2+}(aq)\ +$$SO_4^{2-}\ \rightarrow\ BaSO_4(s)$
• what happens when group 2 hydroxides + carbonates decompose on heating?

  Group 2 hydroxides decompose on heating to oxide + steam

  e.g.$Ca\left(OH\right)_2(s)\ \rightarrow\ CaO(s)\ +$$\ H_2O(g)$

  All group 2 carbonates decompose on heating to oxide + carbon dioxide

  e.g.$MgCO_3(s)\ \rightarrow\ MgO(s)\ +$$\ CO_2(g)$
• What happens to thermal stability as you go down group 2?

  -increases as you go down group.
• At room temperature, What state is chlorine, bromine and iodine?

  Chlorine = green gas

  Bromine = red-brown liquid

  Iodine = grey solid
• What happens to melting + boiling point as you go down group 7?

  -increases

  -number of electrons increases with atomic number = increase in induced dipole-induced dipole intermolecular forces holding diatomic molcule together.
• How do halogens react?

  -By gaining electrons to form negative halide ions.

  -halogens are reduced + oxidise other substances.

  -halogens react directly with most metals to form the halide.

  e.g. $2Na\ +$$\ Cl_2\ \rightarrow\ 2NaCl$
• What is the general trend in reactivity + oxidising power as you go down group 7?

  -decrease

  -outer electrons become more shielded + increased distance from nucleus.

  -harder to attract electrons
• What happens during a displacement reaction?

  -halogen in a higher position in group will oxidise halide ion from lower in the group.

  -more reactive halogen displaces a less reactive halide from its solution

  -colour changes

  e.g. $Cl_2(aq)\ +$$\ 2Br^-(aq)\ \rightarrow\ 2Cl^-(aq)\ +$$\ Br_2(aq)$

  colourless orange
• How do you test for halide ions?

  -add few drops of nitric acid to aq halide ion.

  -add silver nitrate solution (AgNO3)

  -followed by dilute aqueous ammonia

  chloride ion = white precipitate, dissolved fully with diluted ammonia

  bromide ion = cream precipitate, dissolves slightly with diluted ammonia

  iodide ion = yellow precipitate, no change with diluted ammonia
• Why is chlorine gas added to drinking water?

  -kill dangerous bacteria + viruses such as cholera and typhoid

  -needs to be added in low concentrations (below 1 ppm) to be safe
• Why is fluoride added to water?

  -reduce tooth decay by preventing cavities

  -also said to strengthen bones, helps prevent osteoporosis

  -only beneficial when added below 1 ppm
• How are insoluble salts formed?

  -by a precipitate reaction.

  -2 suitable solutions are mixed to form a soluble salt + an insoluble salt.

  e.g. formation of calcium carbonate

  $Ca\left(NO_3\right)_2(aq)\ +$$\ Na_2CO_3(aq)\ \rightarrow\ CaCO_3(s)\ +$$\ 2NaNO_3(aq)$

  -precipitate is filtered, washed + dried
• How are soluble salts formed?

  -formed by neutralising an acid.

  e.g. formation of magnesium sulfate

  $MgO(s)\ +$$\ H_2SO_4(aq)\ \rightarrow\ MgSO_4(aq)\ +$$\ H_2O(l)$

  -excess solid is filtered.

  -solution is evaporated + left to cool to form crystals