Question

The halogens have the smallest atomic radii in their respective periods. The atomic radius of fluorine is extremely small. All halogens exhibit – 1 oxidation state. They are strong oxidising agents and have maximum negative electron gain enthalpy. Among halogens, fluorine shows anomalous behaviour in many properties. For example, electronegativity and ionisation enthalpy are higher for fluorine than expected whereas bond dissociation enthalpy, m.p. and b.p. and electron gain enthalpy are quite lower than expected. Halogens react with hydrogen to give hydrogen halides (HX) and combine amongst themselves to form a number of compounds of the type XX', XX'₃, XX'₅ and XX'₇ called inter-halogens.

1. Why halogens have maximum negative electron gain enthalpy?

2. Why fluorine shows anomalous behaviour as compared to other halogens?

3. Arrange the hydrogen halides (HF to HI) in the decreasing order of their reducing character.

4. Why fluorine is a stronger oxidizing agent than chlorine?

5. What are the sizes of X and X' in the interhalogen compounds?

Answer 1

1. Halogens have maximum negative electron gain enthalpy in their corresponding periods because they have only one electron less than stable noble gas configuration. 

2. The anomalous behaviour of fluorine is due to its small size, highest electronegativity, low F-F bond dissociation enthalpy and non-availability of d-orbitals in valence shell.

3. Reducing character of hydrogen halides varies as

HI > HBr > HCl > HF

4. Because of smaller bond dissociation energy of F-F bond and greater enthalpy of hydration of F– ion, fluorine is a stronger oxidising agent than chlorine.

5. The size of X is greater than that of X' as X is less electronegative than X'.