3.2.3 - the halogens
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Diatomic halogen molecules are held together by …
Weak vdw
Fluroine exists as
Pale yellow gas
Chlorine exists as
Green gas
Bromine exists as
Red brown liquid
Iodine exists as
Grey solid
Trend in boiling points down group 7
Boiling points increase down group 7
Why do bp increase down group 7
Increasing strength of vdw Due increasing size and increased number of electrons more chance of dipoles inducing dipoles in the neighbouring molecules
Chlorine has a low bp bc forces bet mol are weak Explain how these forces arise between molecules of chlorine (3)
Imbalance of of e- density leads to temporary dipole in the mol which induces a dipole im a neighbouring mol These temporary dipoles attract
Trend in bond enthalpies down group 7
Decrease down down the group So i-i bonds easier to break than cl-cl bodnds
Why do bond enthalpies decrease down group 7
This is due to the increasing atomic radius, increased shielding and reduced attraction between the nucleus and bonding pair of electrons
Exception to trend in bond enthalpies down group 7
The exception to this is fluorine. ● Fluorine has such a small atomic radius that bonding and non-bonding electrons repel each other, reducing the strength or bond enthalpy.
Define electronegativity
Power of an atom to attract a bonding pair of electrons in a covalent bond
Trend in electronegativity going down group 7
● Electronegativity of the halogens decreases going down the group.
Explain trend of decreasing electronegativity down group 7
As the atomic radius increases the shared pair of electrons in the covalent bond are further from the nucleus, reducing the strength of the attraction. ● Increasing atomic radius also means increasing shielding effect, again reducing the electronegativity. ● These factors have a greater effect than the increased nuclear charge
trend in boiling points down group 7
increase down the group
explain trend of increasing boiling points down group 7
B.p.s increase down the group because… * Size of diatomic molecules increase down the group. * Larger molecules have more electrons, leading to greater induced dipole-dipole forces. * Therefore greater van der Waals’s forces between molecules. * Therefore more energy required to overcome the greater van der Waals’s forces as you go down the group.
define oxidation agent
electron acceptor
trend in oxidising ability down group 7
decreases down the group
explain trend in decreasing oxidising ability down the group
Oxidising power decreases down the group because… * Size of ions increase down the group. * Therefore outer electrons are more shielded and further away from the nucleus. * Therefore electrostatic force of attraction by nucleus on the additional electron becomes weaker down the group. * Therefore harder to gain an electron.
reactivity down group 7
decreases
explain decreasing reactivity down group 7
increased atomic rad outershel has increased dist from nuclues less electrostatic attraction harder to attract e-
whats is displacment
more reactive halogen will displace a less reactive one
whats observed when chlorine water reacts w kcl kbr ki
kcl - no reac kbr - orange br2 ki - brown i2
whats observed when bromine water reacts w kcl kbr ki
kcl - no reac kbr - no reac ki - brown i2 formed