Draw a Lewis structure for the urea molecule, CO(NH2)2. Draw the Lewis dot structure for urea. Include all lone pairs of electrons. Part B Predict its geometric shape around the C atom with the VSEPR theory. Predict its geometric shape around the N atom with the VSEPR theory. tetrahedral trigonal pyramidal bent trigonal planar Part C Predict its geometric shape around the N atom with the VSEPR theory. Predict its geometric shape around the C atom with the VSEPR theory. tetrahedral trigonal pyramidal bent trigonal planar
The Correct Answer and Explanation is:
Correct Answers:
- Part A: Lewis structure of urea, CO(NH₂)₂, includes all atoms and lone pairs.
- Part B:
- Geometric shape around the C atom: Trigonal planar
- Geometric shape around the N atom: Trigonal pyramidal
- Part C:
- Geometric shape around the N atom: Trigonal pyramidal
- Geometric shape around the C atom: Trigonal planar
Explanation
Urea, with the formula CO(NH₂)₂, consists of a central carbon atom double bonded to an oxygen atom and singly bonded to two amino groups (–NH₂). To analyze its geometry, we first draw its Lewis structure.
Lewis Structure of Urea:
- Carbon (C): 4 valence electrons
- Oxygen (O): 6 valence electrons
- Nitrogen (N): 5 valence electrons × 2 = 10
- Hydrogen (H): 1 valence electron × 4 = 4
Total = 4 + 6 + 10 + 4 = 24 valence electrons
- Carbon forms four bonds: a double bond with oxygen and single bonds with two nitrogen atoms.
- Each nitrogen forms three bonds: one with carbon and two with hydrogen.
- Oxygen has two lone pairs; each nitrogen has one lone pair.
Molecular Geometry (VSEPR Theory)
VSEPR (Valence Shell Electron Pair Repulsion) Theory states that electron pairs around a central atom will arrange themselves to minimize repulsion.
Carbon Atom:
- The carbon is bonded to three atoms: one oxygen and two nitrogens.
- It has no lone pairs.
- With three electron regions, the shape is trigonal planar (bond angles ~120°).
Nitrogen Atom:
- Each nitrogen is bonded to three atoms (one C and two H).
- Each nitrogen has one lone pair, giving it four electron regions.
- The molecular geometry is trigonal pyramidal, similar to ammonia (NH₃).
In conclusion, VSEPR theory predicts a trigonal planar geometry around the carbon atom due to three bonding groups and no lone pairs, and a trigonal pyramidal geometry around each nitrogen due to three bonds and one lone pair. These shapes help determine urea’s structural and chemical behavior, such as hydrogen bonding and polarity.
