inorganic year - 1

electronegativity

tendecy of an atom in a molecule to attract electrons in a covalent bond to itself

melting and boiling points of group 7

• increases down group

• as atoms become larger they have more electrons

• stronger van der waal forces between molecules

• more energy needed to break bonds

oxidising agents

oxidises others reduces itself

oxidising ability in group 7

• oxidising strength decreases down the group

• Because of shielding and a greater atomic radius

what is relative oxidising strength?

halogen will displace any halide ion beneath it in the periodic table

oxidising agent

gains electrons

reducing agent

loses electrons

chlorine

pale green solution

bromine colour

yellow solution

iodine colour

brown solution (sometimes a black solid)

Cl- in dilute and conc NH3

dilute - NH3 - ppt dissolves

conc - NH3 - ppt dissolves

Br- in dilute and conc NH3

dilute - NH3 - no change

conc - NH3 - ppt dissolves

I- - dilute and conc NH3

dilute NH3 - no change

dilute NH3 - no change

Disproportianation

element simultaneously oxidised and reduced

chlorine + water

Cl2(g) + H2O(l) = HClO(aq) + HClaq)

chlorine + water ( in sunlight)

2Cl2 + 2H2O - 4H+ + Cl- + O2

• greenish colour of chlorine water fades & colourless O2 is produced.

Uses of chlorine in water treatment

• kill bacteria

• used to treat drinking water and water in swimming pools

  BENEFITS OUTWEIGH TOXIC RISKS

reaction of chlorine with cold dilute NaOH + uses

Cl2(aq) + 2NaOH(aq)

Cl2(aq) + 2NaOH(aq) - NaCl(aq) + NaClO(aq) + H2O(l)

• mixture of NaCl and NaClO is used to bleach and disinfect/kill bacteria

Disadvantages of chlorine

• harmful to respitory system

• liquid chlorine on skin and eyes can cause severe chemical burns.

• chlorine can react with organic compounds to form chlorinated hydrogens, many are carcinogenic