Draw the Lewis structure and state its molecular shape (Tetrahedral, pyramidal, bent, trigonal planar, or linear) (5 points each, 20 points total). DO NOT FORGET LONE PAIRS. CHBr, C2H2, BrCl3
The Correct Answer and Explanation is:
Here are the Lewis structures and molecular shapes for the given compounds:
1. CHBr (Bromomethylene)
Lewis Structure:
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H–C==Br
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- Carbon has 4 valence electrons, forms 2 bonds: one with hydrogen, one double bond with bromine.
- Hydrogen has 1 valence electron, forms 1 bond.
- Bromine has 7 valence electrons, shares 2 electrons in the double bond and keeps 3 lone pairs.
Molecular Shape: Linear
Carbon in this molecule has only two bonded atoms and no lone pairs, resulting in a linear geometry with a bond angle of about 180°.
2. C₂H₂ (Ethyne or Acetylene)
Lewis Structure:
mathematicaCopyEditH–C≡C–H
- Each carbon has 4 valence electrons, forming a triple bond between them and a single bond with hydrogen.
- Each hydrogen forms 1 single bond.
Molecular Shape: Linear
Each carbon atom is bonded to two regions of electron density (one hydrogen and one carbon), and has no lone pairs, resulting in a linear molecular geometry.
3. BrCl₃ (Bromine Trichloride)
Lewis Structure:
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Cl–Br–Cl
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Cl
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- Bromine (central atom) has 7 valence electrons, forming 3 single bonds with Cl and retaining 2 lone pairs.
- Each Cl atom has 3 lone pairs.
Molecular Shape: T-shaped
Bromine has 5 electron regions (3 bonding pairs and 2 lone pairs). According to VSEPR theory, this leads to a T-shaped geometry.
Explanation
Lewis structures are visual representations of molecules that show how atoms are bonded and where lone pairs of electrons reside. These structures are essential for predicting molecular shape and understanding chemical behavior.
In CHBr, carbon forms two bonds — a single bond with hydrogen and a double bond with bromine. Since carbon is bonded to two atoms with no lone pairs, the electron groups arrange themselves linearly to minimize repulsion. Thus, the molecule is linear.
For C₂H₂, each carbon forms a triple bond with the other carbon and a single bond with hydrogen. This results in two regions of electron density around each carbon. With no lone pairs, these regions arrange in a linear fashion, producing a 180° bond angle.
BrCl₃ is more complex due to bromine’s expanded octet. Bromine is surrounded by 5 electron domains (3 bonding, 2 nonbonding). VSEPR theory tells us that when there are 5 electron regions, the basic geometry is trigonal bipyramidal. However, the presence of two lone pairs pushes the bonding atoms into a T-shaped configuration. The lone pairs occupy equatorial positions to reduce electron repulsion.
Drawing correct Lewis structures and applying VSEPR (Valence Shell Electron Pair Repulsion) theory allows us to determine the molecular geometry, which directly influences properties like polarity, boiling point, and reactivity. Understanding both bonding and lone pair interactions helps predict how molecules behave in different environments.
