Question

What is the geometry of water molecules?
[A] Distorted tetrahedral
[B] Tetrahedral
[C] Trigonal planar
[D] Diagonal

Answer 1

Hint: To find out the geometry of a water molecule, try to find out the hybridisation by the help of VSEPR theory. It does not have a linear structure. The structure is slightly bent due to lone pair repulsion and the bond angle is slightly less than it should be.

Complete answer:
We know that molecular geometry of a molecule is the three dimensional arrangement of the atoms which forms the molecule. The geometry of a molecule helps us understand the general shape of the molecule. It also helps us examine the bond angle, bond length, torsional angles and other geometrical factors.
According to VSEPR theory i.e. valence shell electron pair repulsion theory, the geometry, hybridisation and the coordination number are interrelated.
According to this theory, we can find out the geometry of molecules by the number of electron pairs surrounding their central atom.
In water molecules, as we know there are 2 hydrogen atoms and one oxygen atom. Here, the central atom is oxygen. The atomic number of oxygen is 8. Therefore its electronic configuration is 2, 6.
 We can understand from the electronic configuration that there are 6 electrons in its valence shell.
The two hydrogen atoms contribute 1 electron so for 2 hydrogen atoms, the total contribution of electrons is 2.
Therefore, there is a total contribution of 8 electrons or we can write that 4 electron pairs.
Therefore, the coordination number is 4.
For coordination number 4, the corresponding hybridisation is $s{p}^3$ and the geometry is tetrahedral i.e. the ideal bond angle should be ${109}^{{}^{\circ }}{5}^{{}^{\prime }}$but due to the lone-pair-lone-pair repulsion, the two hydrogen atoms are compressed making a bond angle of ${104}^{{}^{\circ }}{5}^{{}^{\prime }}$. Therefore, water has a bent structure and thus it is considered as a distorted tetrahedral.

Therefore, the correct answer is option [A] Distorted tetrahedral.

Note:
Although VSEPR is quite successful in determining the geometries of molecules, there are certain drawbacks to this theory. This theory fails to determine the shape of isoelectronic species. It also does not take the relative size of the constituents under consideration. It is unable to explain the atomic orbital overlaps.