Question

The $M - O - M$ bond angles in ${M_2}O$ [where M is halogen] is in the order:
A. $Br{O_2} > C{l_2}O > {F_2}O$
B. ${F_2}O > B{r_2}O > C{l_2}O$
C. ${F_2}O > C{l_2}O > B{r_2}O$
D. $C{l_2}O > {F_2}O > B{r_2}O$

Answer 1

Properties of halogens like electronegativity, number of electrons and attraction between bonding pairs will help you get to the answer. Electronegativity is the attraction between bonding pairs of electrons to the atoms.

Complete step by step answer:
Starting with bond angle, we know that bond angle is the angle between two bonds originating from the same atom in a covalent species. Here in this question the bond is originating from an oxygen atom and connected with metal atoms on both the ends. Here we can observe that all the metals i.e. Fluorine, Bromine and Chlorine are the atoms from the same row of periodic table. They are a part of the 17th row or group. They are called Halogens. Now, let’s start with some information about these halogens.

Fluorine is the first element of the halogen group with atomic number 9. It is the lightest and the highly toxic and reactive element. Also, it is the most electronegative element. It reacts with all other elements except for argon, neon and helium.

Next we have Chlorine with atomic number 17. It is the second lightest halogen and a yellow green gas at room temperature. Its properties are between Fluorine and Bromine.

The next one is Bromine. It is the third element in the group and has atomic number 35. It is a fuming red brown liquid at room temperature and evaporates readily to form similar coloured gas.

Talking about bond angle down the group. The bond angles for the oxides of Fluorine, Chlorine and Bromine are ${103.1^ \circ }$ , ${110.9^ \circ }$ and ${112^ \circ }$ respectively. That is, the bond angle increases down the group. This is because as we go down the group, the size of atoms increases thus decreasing the central force. Also, electronegativity decreases from fluorine to bromine and therefore, the bond angles increase. Electronegativity is the attraction of bonding pairs of electrons to the atoms. So, due to high electronegativity of fluorine, the electrons are attracted towards fluorine decreasing the bond angle. And the bond angles increase down the group.

**So the correct option is A.

Note: **
There are various reasons and properties that affect the bond angle of various compounds. For example, the bond angle of ${H_2}O$ is greater than ${F_2}O$ . So we need to keep in mind all of these factors as well as the exceptions .