D11.6 Molecules with More Than One Central Atom

Larger molecules have more than one “central” atom with several other atoms bonded to it. The arrangement of bonds for each central atom can be predicted as described in the preceding sections. The way these local structures are oriented with respect to each other influences the overall molecular shape.

Activity: Molecules with Several Central Atoms

Consider the Lewis structure below, where each central atom is numbered. The structure is not drawn with wedge-dash notation.

A Lewis structure: N-sub-1 bonded to H(left), H(below), C(right), lone pair above; then Cs-ub-2 to N(left), H(below), H(above), C(right); then C-sub-2 to C(left), H(below), H(above), O(right); then O-sub-4 to C(left), H(right), lone pairs above and below.

In your notebook:

  1. Identify the hybridization for each atom (except H atoms) in the structure.
  2. Determine the arrangement of bonds around each atom and describe the local structure.
  3. Indicate whether the structure is three dimensional.
Write in your notebook, then left-click here for an explanation.
  1. N1 is sp3 hybridized
    C2 is sp3 hybridized
    C3 is sp3 hybridized
    O4 is sp2 hybridized
  2. N1 has three bonds arranged as a trigonal pyramid.
    C2 has four bonds pointing to the corners of a tetrahedron.
    C3 has four bonds pointing to the corners of a tetrahedron.
    O4 has two bonds in an angular or bent configuration (nonlinear).
  3. Three of the four central atoms are three-dimensional, so the molecule cannot be planar or linear. The molecule is three-dimensional.

Exercise: Identifying Hybridization

Activity: Predicting Structure of a Molecule with Several Central Atoms

The simple Lewis structure for acetone is shown below. Predict the hybridization and local geometry for all the non-hydrogen atoms. Draw the molecule with correct 3D geometry using the wedge-dash notation.

Lewis structure of acetone

Draw in your notebook, then left-click here for an explanation.

The hybridization and local geometry for each non-hydrogen atom is:

  • C1:  sp3; tetrahedral
  • C2:  sp2; trigonal planar
  • C3:  sp3; tetrahedral
  • O:  sp; linear

The Lewis structure, drawn with wedge-dash notation, is shown below.

A wedge-dash structure for acetone is shown. At the top is an O atom with two lone pairs; it has two bond lines to a C atom. The central C atom has a bond line to a C atom down and to the left and another C atom down and to the right. Each of those C atoms has a bond line in the plane of the screen to one H atom, a wedge bond toward you out of the screen to another H atom, and a dash line behind the screen to a third H atom.

This is one possible perspective; you can draw the acetone molecule in other perspectives (for example, you can choose the perspective where the C=O is pointing down). Click here to see a rotatable 3D structure of acetone; rotate the structure until it matches your drawing.

For simplicity, always draw as many bonds as possible in the plane of the paper/screen. That is, maximize the number of bonds drawn with lines (instead of wedges or dashes).

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Chem 109 Fall 2024 Copyright © by Jia Zhou; John Moore; and Etienne Garand is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.