Question

Determine the shape of the following molecules using the VSEPR model.
$BeC{l_2},BC{l_3},SiC{l_4},As{F_5},{H_2}S$ and $P{H_3}$

Answer 1

Hint: For the determination of shape according to the VSEPR theory one needs to calculate the number of bond pairs and number of lone pairs that are present in the structure. The sum of both the bond pairs and lone pairs will lead to the geometry and shape of that molecule.

Complete step by step answer:
1) Lets us draw the structure according to VSEPR theory as below,
i) $BeC{l_2}$
The valence electrons in Beryllium are two both of which are attached to the chlorine atom Hence it will have two bond pairs no lone pair which will give the Linear shape for the molecule.

ii) $BC{l_3}$
The central atom Boron has three valence electrons and all of them are attached to the three chlorine atoms which give three bond pairs and no lone pair. Hence, the structure will be Triangular planar shape.

iii) $SiC{l_4}$
The central atom Silicon has four valence electrons and all of them are attached to the four chlorine atoms which give four bond pairs and no lone pair. Hence, the structure will be a Tetrahedral shape.

iv) $As{F_5}$
The central atom Arsenic has five valence electrons and all of them are attached to the five fluorine atoms which gives five bond pairs and no lone pair. Hence, the structure will be a Trigonal bipyramid shape.

v) ${H_2}S$
The central atom Sulphur has six valence electrons and two of them are attached to the two hydrogen atoms which give two bond pairs and another four which are unpaired will give two lone pairs. Hence, the structure will be a Bent or V-shaped shape.

vi) $P{H_3}$
The central atom Phosphorus has five valence electrons and three of them are attached to the three hydrogen atoms which give three bond pairs and two unpaired electrons will form one lone pair. Hence, the structure will be a Trigonal pyramidal shape.

Note:
There are some simple steps for determining the structure of a molecule according to VSEPR theory,
i) First decide the central atom present in a structure and its valence electrons.
ii) Now attach the number of atoms or groups which are attached to the central atom as each atom or group for each valence electron.
iii) Each bond formed between the valence electron of the central atom and the other atom or group will give the number of bond pairs.
iv) If there are unpaired valence electrons of the central atom then they will form a lone pair of electrons for two valence electrons.
v) In the last step calculating the sum of the number of bond pairs and number of lone pairs one can decide the shape of the given molecule.