Draw the Lewis structure and state its molecular shape (Tetrahedral, pyramidal, bent, trigonal planar, or linear). A. NH2Br B. H2S C. CSe2 D. BBr3
The Correct Answer and Explanation is:
Let’s go through each compound step by step. We will draw the Lewis structures and determine the molecular shapes based on VSEPR (Valence Shell Electron Pair Repulsion) theory.
A. NH₂Br (Aminobromide)
Lewis Structure:
- Nitrogen (N) has 5 valence electrons.
- Each Hydrogen (H) has 1, total of 2 from both H atoms.
- Bromine (Br) has 7 valence electrons.
Structure:
- N is the central atom.
- Two single bonds with H atoms.
- One single bond with Br.
- One lone pair remains on N.
markdownCopyEdit H
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H — N — Br
:
Electron Groups around N: 4 (3 bonds + 1 lone pair)
Shape: Trigonal pyramidal
B. H₂S (Hydrogen sulfide)
Lewis Structure:
- Sulfur (S) has 6 valence electrons.
- Each H has 1 electron.
Structure:
- S is central atom.
- Two single bonds with H atoms.
- Two lone pairs on S.
markdownCopyEditH — S — H
: :
Electron Groups around S: 4 (2 bonds + 2 lone pairs)
Shape: Bent
C. CSe₂ (Carbon diselenide)
Lewis Structure:
- Carbon (C) has 4 valence electrons.
- Each Selenium (Se) has 6 valence electrons.
Structure:
- C is central atom.
- Forms double bonds with each Se.
- Each Se has two lone pairs.
iniCopyEditSe = C = Se
Electron Groups around C: 2 (2 double bonds)
Shape: Linear
D. BBr₃ (Boron tribromide)
Lewis Structure:
- Boron (B) has 3 valence electrons.
- Each Bromine (Br) has 7 electrons.
Structure:
- B is central atom.
- Forms three single bonds with Br atoms.
- Each Br has three lone pairs.
- No lone pairs on B.
lessCopyEdit Br
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Br—B—Br
Electron Groups around B: 3 (3 bonds)
Shape: Trigonal planar
Explanation
Lewis structures are graphical representations that show the bonding between atoms in a molecule and the lone pairs of electrons that may exist. To draw one, you begin by counting the total number of valence electrons available in the molecule. Then, assign electrons to form bonds and satisfy the octet rule (or duet rule for hydrogen) for each atom.
The molecular shape is determined by the number of electron groups around the central atom. These groups include both bonding pairs (single, double, or triple bonds count as one group) and lone pairs. According to VSEPR theory, electron groups will arrange themselves as far apart as possible to minimize repulsion.
In NH₂Br, nitrogen is surrounded by three bonded atoms and one lone pair, leading to a trigonal pyramidal shape. The lone pair pushes the bonds downward, distorting the shape from a perfect tetrahedron.
H₂S has two bonded atoms and two lone pairs on sulfur, creating a bent shape due to the repulsion from the lone pairs, similar to the structure of water.
In CSe₂, the carbon atom forms two double bonds with selenium atoms and has no lone pairs, so the molecule arranges itself linearly to minimize repulsion.
BBr₃ is an exception to the octet rule; boron is stable with only six electrons. It forms three single bonds and no lone pairs, resulting in a trigonal planar shape with 120-degree bond angles.
These structures help predict molecular polarity, physical properties, and chemical reactivity.
