Discuss the chemistry of halogens, group 17, with specific reference to the reactivity of fluorine. Why does IF 7 exist while ICl 7 doesn’t? Solution The elements of group 17 of the periodic table are known as halogens. The members of the halogen family are F (fluorine), Cl (chlorine), Br (bromine), I (iodine) and As (astatine). The following general characteristics apply to the members of the halogen family. a) F and Cl are gases while Br is a liquid and I is a soft solid at room temperature. As is radioactive and much chemistry about As is yet to be explored. b) All the members of the halogen family are non-metals. This means that the elements have high electronegativity and electron affinity values. The halogens have high ionization energies. All the halogens form ionic salts with metals. Halogens combine with non-metals to form polar covalent bonds and the bond dipole is directed toward the halogen atom in the bond. c) F is the most electronegative element in the group. Infact, F is the most electronegative element in the entire periodic table. The electronegativity of F is so high that it is impossible to oxidize F. On the contrary, F is always reduced to form F - . d) F is the smallest element in the periodic table. Due to small size of F, F has a slightly lower electron affinity than Cl. It is known that electron affinity is the energy released when an electron is added to an neutral gaseous atom. Due to the small size of F, the addition of the extra electron leads to electron-electron repulsions and hence, F has lower electron affinity than Cl. e) F has the highest ionization energy in the group. Infact, the ionization energy of F is so high that it is impossible to remove an electron from F to form F + . f) Due to the small size and high electronegativity of F, F is the only halogen element that can exhibit hydrogen bonding. IF 7 exisits but ICl 7 does not. This can ascribed to the high electronegativity of F. The F atom is more electronegative than Cl. It is due to the high electronegativity of F atom that F can easily polarize I atom to form IF 7 . Cl is more electronegative than I; however, the electronegativity difference is not significant enough to polarize the I atom to form ICl 7 . .

1. Discuss the chemistry of halogens, group 17, with specific reference to the reactivity of fluorine.
Why does IF 7 exist while ICl 7 doesn’t?
Solution
The elements of group 17 of the periodic table are known as halogens. The members of the
halogen family are F (fluorine), Cl (chlorine), Br (bromine), I (iodine) and As (astatine). The
following general characteristics apply to the members of the halogen family.
a) F and Cl are gases while Br is a liquid and I is a soft solid at room temperature. As is
radioactive and much chemistry about As is yet to be explored.
b) All the members of the halogen family are non-metals. This means that the elements have
high electronegativity and electron affinity values. The halogens have high ionization energies.
All the halogens form ionic salts with metals. Halogens combine with non-metals to form polar
covalent bonds and the bond dipole is directed toward the halogen atom in the bond.
c) F is the most electronegative element in the group. Infact, F is the most electronegative
element in the entire periodic table. The electronegativity of F is so high that it is impossible to
oxidize F. On the contrary, F is always reduced to form F -
.
d) F is the smallest element in the periodic table. Due to small size of F, F has a slightly lower
electron affinity than Cl. It is known that electron affinity is the energy released when an electron
is added to an neutral gaseous atom. Due to the small size of F, the addition of the extra electron
leads to electron-electron repulsions and hence, F has lower electron affinity than Cl.
e) F has the highest ionization energy in the group. Infact, the ionization energy of F is so high
that it is impossible to remove an electron from F to form F +
.
f) Due to the small size and high electronegativity of F, F is the only halogen element that can
exhibit hydrogen bonding.
IF 7 exisits but ICl 7 does not. This can ascribed to the high electronegativity of F. The F atom is
more electronegative than Cl. It is due to the high electronegativity of F atom that F can easily
polarize I atom to form IF 7 . Cl is more electronegative than I; however, the electronegativity
difference is not significant enough to polarize the I atom to form ICl 7 .