Questions on Lewis Electron-Dot Structures
Multiple-Choice Questions: Lewis Electron-Dot Structures
1. What do Lewis structures primarily represent?
A) Nuclear structure of atoms
B) Electron configurations
C) Valence electrons and bonding
D) Atomic masses
E) Crystal lattice structures
2. In a Lewis structure, dots are used to represent:
A) Protons
B) Neutrons
C) Valence electrons
D) Bond angles
E) Electron orbitals
3. Which element typically follows the duet rule instead of the octet rule?
A) Oxygen
B) Fluorine
C) Hydrogen
D) Nitrogen
E) Carbon
4. How many valence electrons does oxygen have?
A) 2
B) 4
C) 6
D) 8
E) 10
5. Which of the following atoms typically forms four covalent bonds in a Lewis structure?
A) Fluorine
B) Oxygen
C) Nitrogen
D) Carbon
E) Hydrogen
6. What is the total number of valence electrons in the Lewis structure of CO₂?
A) 8
B) 12
C) 16
D) 20
E) 24
7. In the Lewis structure for water (H₂O), how many lone pairs are on the oxygen atom?
A) 0
B) 1
C) 2
D) 3
E) 4
8. Which element cannot be a central atom in a Lewis structure?
A) Carbon
B) Oxygen
C) Hydrogen
D) Sulfur
E) Phosphorus
9. How many electrons are shared in a double bond?
A) 1
B) 2
C) 4
D) 6
E) 8
10. Which molecule contains a triple bond in its Lewis structure?
A) O₂
B) H₂O
C) NH₃
D) N₂
E) CO₂
11. How many bonding pairs are there in the Lewis structure of CH₄?
A) 1
B) 2
C) 3
D) 4
E) 5
12. What is the total number of electrons represented in the Lewis structure of NH₃?
A) 6
B) 8
C) 10
D) 12
E) 14
13. Which of the following elements is most likely to have an expanded octet in a Lewis structure?
A) Nitrogen
B) Oxygen
C) Carbon
D) Sulfur
E) Fluorine
14. In a correct Lewis structure of carbon dioxide, how many double bonds are present?
A) 0
B) 1
C) 2
D) 3
E) 4
15. In the Lewis structure of BF₃, how many electrons are around the boron atom?
A) 6
B) 8
C) 10
D) 12
E) 14
16. How many lone pairs are on the nitrogen atom in the Lewis structure of NH₃?
A) 0
B) 1
C) 2
D) 3
E) 4
17. Which of the following atoms can exceed the octet rule?
A) Hydrogen
B) Nitrogen
C) Sulfur
D) Carbon
E) Oxygen
18. What is the correct Lewis structure for CH₄?
A) Carbon with four lone pairs
B) Carbon with two single and one double bond
C) Carbon bonded to four hydrogen atoms with single bonds
D) Carbon with two lone pairs and two single bonds
E) Carbon triple-bonded to hydrogen
19. In a Lewis structure, which pair of electrons is involved in bonding?
A) Lone pair
B) Free electrons
C) Valence pair
D) Bonding pair
E) Hybrid pair
20. Why is the octet rule important in drawing Lewis structures?
A) It describes nuclear stability
B) It ensures minimal mass
C) It allows atoms to achieve noble gas configurations
D) It helps determine isotopes
E) It prevents radioactive decay
Answers with Explanations
1. C) Lewis structures show how atoms share valence electrons in molecules.
2. C) Dots in Lewis structures represent valence electrons.
3. C) Hydrogen needs only 2 electrons to be stable (duet rule).
4. C) Oxygen has 6 valence electrons (Group 16 element).
5. D) Carbon typically forms four covalent bonds.
6. C) CO₂ has 4 valence e⁻ from carbon and 6 from each oxygen → 4 + 6×2 = 16.
7. C) The oxygen in H₂O has two lone pairs.
8. C) Hydrogen can’t be central because it forms only one bond.
9. C) A double bond shares 4 electrons (2 bonding pairs).
10. D) N₂ has a triple bond between nitrogen atoms.
11. D) CH₄ has 4 single bonds, thus 4 bonding pairs.
12. C) NH₃ has 5 from N and 1 from each H → 5 + 3 = 8 electrons.
13. D) Sulfur can have an expanded octet due to its empty d-orbitals.
14. C) CO₂ has two double bonds, one with each O.
15. A) BF₃ has only 6 electrons around boron, making it an exception.
16. B) Nitrogen in NH₃ has one lone pair.
17. C) Sulfur can exceed the octet rule.
18. C) CH₄ has a carbon atom with four single bonds to H.
19. D) A bonding pair is a pair of shared electrons between two atoms.
20. C) The octet rule helps atoms attain noble gas-like stability
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