Group 7
Each of the halogens have 7 electrons in the highest energy level
Halogens exist as diatomic molecules with the general formula X 2 where molecules are held
together by weak Van der Waal forces
Trend in melting points – INCREASE
o Molecules get larger – have more electrons
o More chance of instantaneous dipole
o Greater Van der Waal forces between molecules
Trend in electronegativity – DECREASE
o Increase in number of energy levels, increased atomic radius
o More shielding
o Less attraction between nucleus and bonding pair of electrons
Trend in bond enthalpy – DECREASE
o Atomic radius increases
o Bonding electrons are further from the nucleus
o Less attraction between bonding pair of electrons and nucleus
o EXCEPTION – F-F bond
F-F bond is very weak
Small size of fluorine atoms leads to repulsion between non-bonding electrons
as they are so close together
Oxidising Power of Halogens
Oxidising agent – Electron acceptor
Halogens readily accept electrons to form halide ions
When a halogen accepts an electron it is reduced
X2 + 2e– -> 2X–
Trend in oxidising power – DECREASE
o Increase in number of energy levels
o Increase in atomic radius
o Increase in shielding
o Decrease in ability to attract an electron
o Can be observed during displacement reactions – more reactive halogen with displace a
less reactive one from its salt solution
o Trend – Cl2 (strongest) -> Br2 -> I2 (weakest)
o Fluorine not looked at in aqueous solution as it reacts violently with water
Reducing Power of Halides
Reducing agent – electron donor
Halide ions can lose electrons to form the halogen. When the halide ion donates an electron it is
oxidised (loses electrons)
2X– -> X2 + 2e–
Each of the halogens have 7 electrons in the highest energy level
Halogens exist as diatomic molecules with the general formula X 2 where molecules are held
together by weak Van der Waal forces
Trend in melting points – INCREASE
o Molecules get larger – have more electrons
o More chance of instantaneous dipole
o Greater Van der Waal forces between molecules
Trend in electronegativity – DECREASE
o Increase in number of energy levels, increased atomic radius
o More shielding
o Less attraction between nucleus and bonding pair of electrons
Trend in bond enthalpy – DECREASE
o Atomic radius increases
o Bonding electrons are further from the nucleus
o Less attraction between bonding pair of electrons and nucleus
o EXCEPTION – F-F bond
F-F bond is very weak
Small size of fluorine atoms leads to repulsion between non-bonding electrons
as they are so close together
Oxidising Power of Halogens
Oxidising agent – Electron acceptor
Halogens readily accept electrons to form halide ions
When a halogen accepts an electron it is reduced
X2 + 2e– -> 2X–
Trend in oxidising power – DECREASE
o Increase in number of energy levels
o Increase in atomic radius
o Increase in shielding
o Decrease in ability to attract an electron
o Can be observed during displacement reactions – more reactive halogen with displace a
less reactive one from its salt solution
o Trend – Cl2 (strongest) -> Br2 -> I2 (weakest)
o Fluorine not looked at in aqueous solution as it reacts violently with water
Reducing Power of Halides
Reducing agent – electron donor
Halide ions can lose electrons to form the halogen. When the halide ion donates an electron it is
oxidised (loses electrons)
2X– -> X2 + 2e–
