The Lewis structure for allene is Make a sketch of the...

The Lewis structure for allene is Make a sketch of the structure of this molecule that is analogous to Figure $9.27 .$ In addition, answer the following three questions: (a) Is the molecule planar? (b) Does it have a nonzero dipole moment? (c) Would the bonding in allene be described as delocalized? Explain.

The Lewis structure for allene is
Make a sketch of the structure of this molecule that is analogous to Figure $9.27 .$ In addition, answer the following three questions: (a) Is the molecule planar? (b) Does it have a nonzero dipole moment? (c) Would the bonding in allene be described as delocalized? Explain.

Key Concepts

Lewis Structures

Lewis structures are diagrams that represent the bonding between atoms and the lone pairs of electrons that may exist in a molecule. They are essential for visualizing molecular connectivity, evaluating formal charges, and predicting the arrangement of bonds. In the context of allene, drawing the Lewis structure helps in understanding how the carbon atoms are connected through double bonds and in illustrating the distribution of electrons around the atoms.

Molecular Geometry and Hybridization

Molecular geometry refers to the three-dimensional arrangement of atoms in a molecule, which is largely determined by the hybridization of the central atoms and the distribution of electron density. In allene, the central carbon is sp-hybridized, which leads to a linear arrangement for the central atom but causes the attached groups to lie in perpendicular planes. Understanding hybridization is crucial for predicting the spatial orientation of bonds and the overall shape of the molecule.

Molecular Polarity (Dipole Moment)

The dipole moment of a molecule arises from differences in electronegativity between atoms and the spatial arrangement of polar bonds. Even when individual bonds are polar, a molecule can be nonpolar if the molecular geometry allows for an even distribution and cancellation of these dipoles. In the case of allene, symmetry ensures that any individual bond dipoles cancel, resulting in a net dipole moment of zero despite the presence of double bonds.

Delocalization of ? Bonds

Delocalization involves the sharing of electrons over multiple atoms or bonds, often seen in conjugated systems where adjacent p orbitals overlap. However, in allene the ? bonds are formed from p orbitals that are orthogonal to each other, which means they do not overlap to create a continuous delocalized system. As a result, the two ? bonds in allene remain localized and behave independently rather than being delocalized over the molecule.

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