Interpretation & Concept Introduction:
the Lewis structure and assign formal charges of each atom in Formamide and methylformate.
Answer to Problem 4.114QA
Solution:
a) Lewis structure:
i. Formamide (HCONH2)
ii. Methyl formate (HCO2CH3)
b) The net formal charge of compound methyl formate is 0.
Explanation of Solution
The electronic configuration of the elements H, C N and O is as follows.
H: 1s1.
C: 1s2 2s2 2p2.
N: 1s2 2s2 2p3.
O: 1s2 2s2 2p4.
i. Lewis structure of Formamide (HCONH2)
Element | Valence electrons | ||
Symbol | # of atoms | In one atom | Total |
H | 3 | 1 | 3 |
C | 1 | 4 | 4 |
N | 1 | 5 | 5 |
O | 1 | 6 | 6 |
Valence electrons in molecule | 18 |
First we draw a skeletal structure of the molecule.
There are five bonds in the skeletal structure. Therefore 5x2 = 10 electrons are involved in the bond formation. To complete the octet of O and N we will put electron pairs on them.
To complete the octet of C we shift one of the lone pair on O as bond pair between C and O. This completes the octet of C as well as O.
This gives us the Lewis structure of formamide.
ii. Lewis structure of methyl formate (HCO2CH3)
Element | Valence electrons | ||
Symbol | # of atoms | In one atom | Total |
H | 4 | 1 | 4 |
C | 2 | 4 | 8 |
O | 2 | 6 | 12 |
Valence electrons in molecule | 24 |
First we draw a skeletal structure of the molecule.
There are seven bonds in the skeletal structure. Therefore 7x2 = 14 electrons are involved in the bond formation. To complete the octet of O we will put electron pairs on them.
To complete the octet of C we shift one of the lone pair on O as bond pair between C and O. This completes the octet of C as well as O
This gives us the Lewis structure of methyl formate.
c) Calculating formal charges:
1) Formula:
FC = (no. of valence electrons) – [no. of electrons in lone pairs + ½ (no. of shared electrons]
2) Calculations:
Formal charge on each atom of compound (a) is calculated as:
The net formal charge on compound formamide is 0.
Formal charge on each atom of compound methyl formate is calculated as:
The net formal charge of compound methyl formate is 0.
Conclusion:
By using the Lewis structure, formal charges are calculated for each atom in formamide and methyl formate.
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