# Predict the approximate molecular geometry around each carbon atom of acetonitrile:

Predict the approximate molecular geometry around each carbon atom of acetonitrile:

General guidance

Concepts and reason
The structure of acetonitrile is given in which molecular geometry of the carbon atom needs to be marked. Identify the hybridization of the carbon atoms present in acetonitrile by steric number, and then deduce the geometry according to the hybridization.

Fundamentals

Hybridization is the process of mixing the atomic orbitals of comparable energies in an atom to generate a set of new atomic orbitals which are equal in energy and shape is called hybridization.
To determine the steric number for calculating the hybridization of an atom, count the number of bond pairs + lone pairs which gives the type of orbitals involved in hybridization. The hybridization and the corresponding geometry resulting from the hybridization is listed below:

Only single bonds and lone pairs are included in determining hybridization. Double bonds and triple bonds are not used in determining the steric number as well as the geometry of the molecule.

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Step-by-step

Step 1 of 2

Draw the given structure and label the geometry of left carbon atom in acetonitrile by calculating steric number as shown below:

The steric number for left carbon atom is 4. Therefore, the hybridization is and the corresponding geometry is tetrahedral.

The electronic configuration of carbon is , this implies that carbon atom has four valence electrons.
Now, in the structure left carbon atom is bonded to three hydrogens and one carbon atom, therefore, the number of bond pair is equal to four. As all the valence electrons are used in forming the bonds so, there is no lone pair left. Thus,

Therefore, the orbitals that participate in hybridization is one orbital and three orbitals. Hence, the hybridization of left carbon atom is and the geometry corresponding to the hybridization is tetrahedral.
Therefore, in general for carbon atom having no multiple bond indicates hybridization, .

Step 2 of 2

Draw the given structure and label the geometry of right carbon atom in acetonitrile by calculating steric number as shown below:

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The steric number for right carbon atom is 2. Therefore, the hybridization is and the corresponding geometry is linear.

The right carbon atom is bonded to one carbon atom and one nitrogen atom, therefore, the number of bond pair is equal to two (multiple bonds are not included in determining steric number). As two valence electrons are used in forming the single bonds and the remaining two are used to form the multiple bonds. Thus,

Therefore, the orbitals that participate in hybridization is one orbital and one orbital. Hence, the hybridization of right carbon atom is and the corresponding hybridization is linear.
Therefore, in general for carbon atom having a triple bond indicates hybridization, .

Do not count multiple bonds while calculating bond pairs. The steric number calculated as 4 for right carbon atom including multiple bond as bond pairs is incorrect.

Steric Number Hybridization Geometry (bond pair of electrons + lone pair of electrons) sp Linear 2 Trigonal planar 3 sp sp Tetrahedral 4
Left C atom CEN Н.С |Tetrahedral
sp
1s22s22p3
Steric number of left C atom bond pair + lone pairs -4+0 =4
р
sp
sp
sp
Right C atom CEN Н.С- Linear
sp
Steric number of right carbon atom = bond pair +lone pairs =2+0 2
р
sp
sp
Right C atom Left C atom lnear lnear bent bent trigonal planar trigonal planar trigonal pyramidal trigonal pyramidal tetrahedral tetrahedral
Right C atom Left C atom lnear lnear bent bent trigonal planar trigonal planar trigonal pyramidal trigonal pyramidal tetrahedral tetrahedral
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