Group VIIA elements (Halogens) and their physical and chemical properties

Group VII elements

Atomic Radii

Trends in atomic radii

Reason

Electronegativity

Units

Trends

Reason

Melting point and boiling points

Question: Why F₂ is a gas and I₂ is solid?

Reason

Melting point and boiling point

Melting and boiling points of halogens increases down the group because instantaneous dipole-induced dipole forces (Vender Wall forces) becomes stronger due to increase in atomic size and mass and hence size is small for F₂ large for I₂ . Therefore, F₂ is a gas and Iodine is solid.

Bond enthalpy

Amount of energy required to break one mole of covalent bond to produce an individual atom is called bond enthalpy.

Cl-Cl -------------- > 2Cl^- + Bond enthalpy

Question: Why bond theory of F₂ is low as compared to the other group elements?

Answer

Reason: This is due to the fact that atomic size of chlorine very small and have two molecules so repulsion between non burning electron as well as between two nuclei is very high. This makes F-F bond very weak and helps in breaking F-F bond into F atoms. That's why bond bond enthalpy of F₂ is very low.

Strength of halogens as oxidizing agent

Halogens have very high oxidizing power due to the high electronegativity (a tendency to attract a shared pair of electrons). The oxidizing property of halogen can be represented by:

½ X₂ + e^- ----------- > X^- + energy

As electron affinity of halogen decreases down the group, oxidizing power also decreases. It decreases in following order.

F₂> Cl₂ > Br₂ > I₂

_Examples

F₂ + 2Cl^- ---------> 2F^- + Cl₂

F₂+ 2NaCl --------- > NaF + Cl₂

Cl₂ + 2Br^- ------------> 2Cl^- + Br₂

Br₂ + 2I^- ------------> 2Br^- + I2

Acidity of hydrogen halide

Question: Why HF is a vehicle is said among other hydrogen halide?

HF <HCl < HBr < HI

Reason all the FS highly electronegative than other halogen but HF with the vehicle asset this is due to the following reason

I. HF makes hydrogen bonding so it doesn't release hydrogen easily so it is a weaker.

II. HF has high Bond enthalpy as compared to other halogen halide due to small size of fluorine atom.

III. Can't you get bases of HF is very strong so it is its acids week.

Halide and as reducing agent

Redox reaction of allied and with concentrated sulphuric acid

Cl- dil H2SO4 ---------- > Na2SO4 + 2HCl

ii. Bromide ion

NaBr + Conc. H2SO4 –---------- > Na2SO4 + HBr

HBr + H2SO4 ------- > Br2 + SO2 + H2O

iii. Iodine

NaI + Conc. H2SO4---- > Na2SO4 + HI

HI + H2SO4 ------- > I2 + H2S + 4H2S + 4H2O

Trends.

Reducing power of halide ions increases in following order.

F- < Cl- < Br- < I-

Reducing power of halide ions increases down the group.

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