Question

The total number of electrons and the number of electrons involved in the formation of various bonds present in one molecule of propanal ( C2H5CHO) are respectively
(a) 32 and 20
(b) 24 and 20
(c) 24 and 18
(d) 32 and 18

Answer 1

Heya !!

Here's the answer!

C2H5CHO

1) Total number of electrons:

Total number of electrons in one C atom is 6, so in 3 C atoms, total number of electrons is 3×6 = 18 e

Similarly, in 1 O atom, 8 e are present

And in 1 H atom, 1 e is present, so in 6 H atoms, 6 e are present.

Therefore, total number of electrons present in one molecule of propanal (C2H5CHO) or (C3H60) is

= 18 + 8 + 6

= 32 electrons.

2) Number of electrons involved in bond formation,

In one C atom, the valence shell electrons = 4, so number of electrons involved in bond formation = valence shell electrons = 4 (for 1 C atom)

For 3 C atoms, electrons involved in bond formation = 3 × 4 = 12.


Similarly, in case of 1 O atoms, valence shell electrons = 6.
But 2 pairs of electrons are not involved in bond formation, the remain as lone pairs.
So, number of electrons involved in bond formation = 6 - 4 = 2

And for 1 H atom, electrons involved in bond formation = 1
So, for 6 H atoms, electrons involved in bond formation = 1 × 6 = 6

Therefore, total number of electrons involved in bond formation in one molecule of propanal
= 12 + 2 + 6

= 20.

☛ Thus, the answer is 32 and 20.

Answer 2

Option (a)

Propanal  C₂ H₅ CHO

Electronic structure and bonds are best understood by a diagram indicating the bonds among various elements in the molecule.

Structure of Propanal is:

                  H    H     H
                   |      |      |
                  C = C  -  C - O - H
                   |              |
                  H            H
 
Total number of single bonds: 8
Total number of double bonds : 1
Number of Electrons involved in the bonds are: 8 * 2 + 1 * 4 = 20


Hydrogen:  1s¹                   Z = 1
Carbon:      1s² 2s² 2p²   :   Z = 6
Oxygen:     1s²  2s² 2p⁴  :   Z = 8

Total number of electrons present in the molecule:
   =  3 * 6 + 1 * 6 + 8
   = 32

So option (a)