To draw the Lewis structure for CH3O (methanol), we start by calculating the total number of valence electrons available. Carbon (C) has 4 valence electrons, each hydrogen (H) has 1, and oxygen (O) has 6. Therefore, the total number of valence electrons is:
4 (C) + 3 x 1 (H) + 6 (O) = 4 + 3 + 6 = 13 valence electrons.
Next, we begin to arrange the atoms. Carbon is the central atom since it is less electronegative than oxygen. The structure will be:
H
|
H – C – O
|
H
In this arrangement, carbon is bonded to three hydrogen atoms and has a single bond to oxygen. To fulfill oxygen’s octet, we need to add two more electrons as a lone pair:
H
|
H – C – O:
|
H
Now we count the electrons:
– Each hydrogen shares 1 electron with carbon (3 pairs from H-C bonds) = 6 electrons from H
– The C-O bond contains 2 electrons, shared with oxygen = 2 electrons
– Oxygen has 2 lone pair electrons = 2 electrons
Total: 2 (C-O) + 3 (H-C) + 2 (O lone pairs) = 13 total valence electrons.
Now that we have the correct Lewis structure, we can determine the formal charge for each atom using the formula:
Formal Charge = Valence Electrons – (Non-bonding Electrons + 0.5 x Bonding Electrons)
For Carbon (C):
Valence Electrons: 4
Non-bonding Electrons: 0
Bonding Electrons: 3 x 2 (C-H) + 2 (C-O) = 8
Formal Charge = 4 – (0 + 0.5 x 8) = 4 – 4 = 0
For Hydrogen (H):
Valence Electrons: 1
Non-bonding Electrons: 0
Bonding Electrons: 2 (H-C)
Formal Charge = 1 – (0 + 0.5 x 2) = 1 – 1 = 0
This is true for each of the three hydrogen atoms.
For Oxygen (O):
Valence Electrons: 6
Non-bonding Electrons: 4 (2 lone pairs)
Bonding Electrons: 2 (C-O)
Formal Charge = 6 – (4 + 0.5 x 2) = 6 – 5 = 1
So, the final formal charges are:
- Carbon (C): 0
- Hydrogen (H): 0
- Oxygen (O): 1
In summary, the Lewis structure of CH3O is valid, and the formal charges for carbon and hydrogen are 0, while oxygen has a formal charge of +1.