Question

$BeF_{2}$ and $H_{2}O$ both are triatomic molecules but their shapes are different. Explain.

Answer 1

$Be{ F }_{ 2 }\quad$ and$\quad { H }_{ 2 }O$are triatomic molecule but the shape of the molecule is linear.

The shape of the molecule $Be{ F }_{ 2 }\quad$ and$\quad { H }_{ 2 }O$ can be explained by the VSEPR(Valency shell electron repulsion).

In $Be{ F }_{ 2 }\quad$, the central element is Beryllium.

Beryllium electronic configuration is $1{ s }^{ 2 }2{ s }^{ 2 }$ and Fluorine electronic configuration $1{ s }^{ 2 }2{ s }^{ 2 }2{ p }^{ 5 }$. Each fluorine atom requires only one electron to get octet electronic configuration. Therefore, two bond pairs are repelled to each other resulting to give linear shape of the molecule.

In ${ H }_{ 2 }O$, the central atom is oxygen electronic configuration is $1{ s }^{ 2 }2{ s }^{ 2 }2{ p }^{ 4 }$.The two electrons from two oxygen atoms are bond with two hydrogen atoms. The four electron pairs  lies around central oxygen atom. Among these two are bonding pairs and two are lone pairs resulting ${ H }_{ 2 }O$ molecule geometry tetrahedral and shape is bent. Angle is 104.${ 5 }^{ 0 }$.