CH3COCN is an organic molecule containing methyl, carbonyl, and cyano functional groups. Its Lewis structure defines the valence electron distribution, covalent bonding modes, and lone pair arrangements, which fundamentally determine the molecule's structural stability and chemical reactivity.

1. Total Valence Electrons Calculation

The first step in constructing the Lewis structure of CH3COCN is calculating total valence electrons based on elemental valence properties. Carbon has 4 valence electrons, hydrogen has 1, oxygen has 6, and nitrogen has 5. The CH3COCN molecule contains four carbon atoms, three hydrogen atoms, one oxygen atom, and one nitrogen atom. The total number of valence electrons is calculated as follows: 4 multiplied by 4 equals 16, plus 3 multiplied by 1 equals 3, plus 6, plus 5, giving a total of 30 valence electrons.

It should be noted that the molecule contains four carbon atoms: the methyl carbon, the carbonyl carbon, and the cyano carbon, not three. All subsequent bonding and lone pair arrangements comply with the octet rule for heavy atoms and the duet rule for hydrogen atoms to achieve stable electron configuration.

2. Skeletal Atomic Arrangement

The atomic skeleton of CH3COCN follows the condensed structural formula sequence: H3C single bond C double bond O single bond C triple bond N.

Specifically, the first carbon atom, namely the methyl carbon, forms three C-H single bonds and connects to the carbonyl carbon. The second carbon atom, namely the carbonyl carbon, acts as the molecular bridge, bonding with the methyl carbon via a single bond, with one oxygen atom via a double bond, and with the cyano carbon via a single bond. The third carbon atom, namely the cyano carbon, forms a single bond with the carbonyl carbon and a triple bond with the nitrogen atom.

Regarding geometry, the carbonyl carbon is sp2 hybridized with a bond angle of approximately 120 degrees, so the C-C(=O)-C skeleton is a planar bent structure rather than linear. Only the C≡N terminal portion is linear.

3. Bonding and Lone Pair Distribution

The bonding electron distribution is as follows: three C-H single bonds contribute 6 electrons, two C-C single bonds (methyl-carbonyl and carbonyl-cyano) contribute 4 electrons, one C=O double bond contributes 4 electrons, and one C≡N triple bond contributes 6 electrons. The total bonding electrons amount to 20.

With 30 total valence electrons, the lone pair electrons total 10, which corresponds to 5 pairs. The specific lone pair distribution is: the carbonyl oxygen carries 2 lone pairs, and the cyano nitrogen carries 1 lone pair. All hydrogen atoms have no lone pairs, and all carbon atoms have no lone pairs.