11) How many lone pairs of electrons are on the S atom in SF4 ?
A) 0
B) 1
C) 2
D) 3
12) How many lone pairs are on the Br atom in BrCl2-?
A) 0
B) 1
C) 2
D) 3
13) In the best Lewis structure for NO +, what is the formal charge on the N atom?
A) -1
B) 0
C) +1
D) +2
4.3 Short Answer Questions
1) Among the compounds H3C–CH3, H2C=CH2, and HCCH, the compound with the strongest carbon-carbon bond is ________, and the compound with the longest carbon-carbon bond is ________.
2) Ionic compounds consist of a single three-dimensional network of ions that are attracted to one another by strong ________ and usually exist in the solid state at room temperature, whereas covalent compounds consist of molecules that are attracted to one another by weak ________ and can exist in gaseous, liquid, or solid state at room temperature.
3) Of the bonds C–C, C–N, C–O, and C–F, the bond that is most polar is ________.
4) The Lewis electron-dot structure of N2 has ________ nonbonding electrons pairs, ________ bonding electron pairs, and a bond order of ________.
5) The Lewis electron-dot structure of H2CO has ________ nonbonding electron pairs, ________ bonding electron pairs, and a carbon-oxygen bond order of ________.
6) The number of Lewis electron dot resonance structures required to describe NO2– is ________.
7) Based on formal charges, the best Lewis electron-dot structure of BF3 has a B–F bond order = ________.
The Correct Answer and Explanation is :
Answers and Explanations:
11) How many lone pairs of electrons are on the S atom in SF₄?
Answer: B) 1
Explanation:
- Sulfur (S) in SF₄ has 6 valence electrons.
- Each fluorine atom forms a single bond with sulfur, using 4 electrons.
- The remaining 2 electrons form a lone pair on sulfur.
- SF₄ adopts a seesaw geometry due to this lone pair.
12) How many lone pairs are on the Br atom in BrCl₂⁻?
Answer: D) 3
Explanation:
- Bromine (Br) has 7 valence electrons. In BrCl₂⁻:
- Each chlorine atom forms a single bond with Br, using 2 electrons total.
- The extra negative charge adds 1 electron.
- This leaves 6 electrons, or 3 lone pairs, on the Br atom.
13) In the best Lewis structure for NO⁺, what is the formal charge on the N atom?
Answer: C) +1
Explanation:
- The nitrogen-oxygen (NO⁺) molecule has 10 total valence electrons (N: 5, O: 6, and -1 due to the positive charge).
- A triple bond forms between N and O, with one lone pair on O.
- Formal charge on N = (5 valence electrons) – (2 nonbonding + 3 bonding pairs) = +1.
4.3 Short Answer Questions
1) The compound with the strongest carbon-carbon bond is HC≡CH, and the compound with the longest carbon-carbon bond is H₃C–CH₃.
Explanation:
- Triple bonds (HC≡CH) are stronger than double (H₂C=CH₂) and single bonds (H₃C–CH₃).
- Single bonds are longer than double or triple bonds.
**2) Ionic compounds consist of a single three-dimensional network of ions that are attracted to one another by strong *electrostatic forces*, and covalent compounds consist of molecules that are attracted to one another by weak **intermolecular forces.
3) The bond that is most polar is C–F.
Explanation:
- Electronegativity difference between C (2.5) and F (4.0) is greater than for the other bonds.
4) The Lewis electron-dot structure of N₂ has:
- Nonbonding electron pairs = 2
- Bonding electron pairs = 3
- Bond order = 3
Explanation:
- N₂ has a triple bond and one lone pair on each nitrogen atom.
5) The Lewis electron-dot structure of H₂CO has:
- Nonbonding electron pairs = 2
- Bonding electron pairs = 4
- Carbon-oxygen bond order = 2
Explanation:
- H₂CO has a double bond between C and O, with 2 lone pairs on O.
6) The number of Lewis electron dot resonance structures required to describe NO₂⁻ is 2.
Explanation:
- Resonance occurs due to delocalized electrons in the N=O bonds.
7) Based on formal charges, the best Lewis electron-dot structure of BF₃ has a B–F bond order = 1.
Explanation:
- BF₃ has no resonance and all B–F bonds are single, as boron lacks an octet in this configuration. Formal charges are minimized this way.