Increasing X-Se-X Bond Angle in SeF₂, SeO₂, and SeCl₆

When comparing the X-Se-X bond angle in the molecules SeF₂, SeO₂, and SeCl₆, it is important to consider the influence of electron pair repulsion on the bond angles. The X represents the outer atoms in each molecule, and in this case, the X-Se-X angle is determined by the arrangement of atoms and lone pairs around the central selenium atom.

Explanation of the Bond Angles:

In SeF₂, there are lone pairs on the selenium atom, which results in the smallest bond angles among the three molecules. The presence of lone pairs causes increased electron pair repulsion, leading to a decrease in bond angle compared to molecules without lone pairs.

SeO₂ has double bonds between the selenium and oxygen atoms, which causes the molecule to have a bent shape. This bent shape results in larger bond angles compared to SeF₂, as the double bonds and lone pairs occupy more space and cause less repulsion between the bonding pairs.

SeCl₆ is an octahedral molecule with single bonds and no lone pairs on the selenium atom. The absence of lone pairs leads to the largest bond angles of 90° in SeCl₆, as there is no additional repulsion from lone pairs or multiple bonds.

Based on the electron pair repulsion effects of lone pairs and multiple bonds on the X-Se-X bond angles, the correct order of increasing bond angle is SeF₂ < SeO₂ < SeCl₆. This order reflects the differences in bond angles influenced by the molecular structures of SeF₂, SeO₂, and SeCl₆.