Periodicity

• how does atomic radius change across period 3?

  outer electrons are in the same shell

  increased number of protons in the nucleus but same amount of shielding

  stronger attraction between outer shell electrons and nucleus

  outer shell electrons are pulled loser to nucleus

  overall decrease
• what is electronegativity?

  ability of an atom to attract two electrons in a covalent bond
• how does electronegativity change across period 3?

  more protons in nucleus

  smaller atomic radius across period

  stronger attraction between nucleus and bonding electrons

  electronegativity increases
• ionisation energy

  energy required to move one mole of electrons from a gaseous atom or ion
• what group of elements are reducing agents

  group two
• when are redox reactions most common?

  when the metal is oxidised to form a 2+ ion
• reactions with water form...

  hydroxides and hydrogen gas
• reactions with acids forms...

  salt and hydrogen gas
• how does reactivity change down the group?

  increases down the group because the ionisation energy decreases down the group
• reaction of group two elements and water forms...

  alkaline solutions because they release OH- ions
• solubility of group 2 hydroxides...

  increases down the group, releasing more OH- ions (this gives the alkaline solution)
• how do halogens react?

  they are reduced to form a halide ion and give a full outer shell
• reactivity down the halogen group

  halogens become less reactive down the group as the tendency to gain electrons decreases.
• qualitative analysis

  used to identify the presence of a substance
• carbonate test for presence of carbonate ions

  add acid which will react with carbonate to form CO2

  bubble gas through limewater which will turn cloudy
• sulfate test for sulfate ions

  add few drops of nitric acid

  add barium nitrate

  white precipitate of barium sulfate will form
• halide test for presence of halide ions

  add a few drops of nitric acid

  add silver nitrate

  precipitate will form either white (AgCl), cream, (AgBr), or yellow (AgI)
• ammonium test for ammonium ions

  add NaOH (aq) to release NH3

  warm solution to liberate the gas.

  test gas with universal indicator paper, which will turn blue
• group 1


  alkali metals
• group 2


  alkaline earth metals
• group 3-12


  transition elements
• group 7


  halogens
• group 0


  noble gases
• ionisation energy


  how easily an atom loses electrons to form positive ions
• factors affecting ionisation energy


  atomic radius

  nuclear charge

  electron shielding
• He -> He+ + e-


  first ionisation energy
• He+ -> He2+ + e-


  second ionisation energy
• successive ionisation energies allow predictions to be made about:


  number of electrons in outer shell

  group of the element in the periodic table

  identity of an element
• how does the reaction trend down group 2

  reaction becomes more vigorous because ionisation energy decreases~
• group 2 element + acid

  forms salt and hydrogen gas
• why do group 2 elements become more reactive down the group

  nuclear radius increases

  shielding increases

  weaker attraction

  reactivity increases
• group 2 oxides + water

  forms alkaline solutions because they release OH- ions
• solubility of group 2 hydroxides

  increases down the group, releasing more OH- ions
• fluorine properties


  pale yellow gas
• bromine properties


  brown liquid that dissolves in water
• iodine properties


  grey crystalline solid, partially soluble in water
• halogen reactivity trend down the group

  become less reactive because the tendency to gain electrons decreases
• Br2 + 2e- > 2Cl-
• halogens as oxidising agents

  down the group, elements become poorer oxidising agents because they get less reactive. there is less shielding so increased nuclear attraction.

  fluorine is strongest, iodine is poorest oxidising agent
• halides as reducing agents

  outer electron is weakly held so it is good at giving its outer electron away. radius is larger down the group so more shielding. iodine is strongest halide as a reducing agent