CHEM 233 MIDTERM EXAM QUESTIONS & ANSWERS WITH COMPLETE SOLUTIONS | 2026 UPDATE

CHEM 233 MIDTERM EXAM QUESTIONS &
ANSWERS WITH COMPLETE SOLUTIONS | 2026
UPDATE

SECTION 1: STRUCTURE, BONDING & HYBRIDIZATION
(Questions 1-25)

Question 1
What is the hybridization of carbon in methane (CH₄)?
A) sp
B) sp²
C) sp³
D) sp³d

Correct Answer: C

Rationale: Methane has four single bonds and tetrahedral geometry. The carbon atom
uses sp³ hybridization (one s orbital + three p orbitals) to form four equivalent sp³
hybrid orbitals. The bond angle is 109.5° .


Question 2
What is the hybridization of each carbon in ethylene (C₂H₄)?
A) sp
B) sp²
C) sp³
D) sp³d

Correct Answer: B

Rationale: Each carbon in ethylene is bonded to three atoms (two hydrogens and one
carbon) with trigonal planar geometry. sp² hybridization involves one s orbital and two p
orbitals. The π bond in the double bond forms from unhybridized p orbitals .

,Question 3
What is the hybridization of each carbon in acetylene (C₂H₂)?
A) sp
B) sp²
C) sp³
D) sp³d²

Correct Answer: A

Rationale: Each carbon in acetylene is bonded to two atoms (one hydrogen and one
carbon) with linear geometry (180° bond angle). sp hybridization involves one s orbital
and one p orbital .


Question 4
Which bond is the shortest?
A) C-C single bond
B) C=C double bond
C) C≡C triple bond
D) All are the same length

Correct Answer: C

Rationale: Triple bonds are shorter than double bonds, which are shorter than single
bonds. C≡C bond length is about 1.20 Å, C=C is about 1.34 Å, and C-C is about 1.54 Å .


Question 5
The bond angle around an sp³-hybridized carbon is approximately:
A) 90°
B) 109.5°
C) 120°
D) 180°

Correct Answer: B

Rationale: sp³ hybridization results in tetrahedral geometry with bond angles of 109.5°.
This is seen in alkanes and saturated carbons .

,Question 6
The bond angle around an sp-hybridized carbon is:
A) 90°
B) 109.5°
C) 120°
D) 180°

Correct Answer: D

Rationale: sp hybridization results in linear geometry with bond angles of 180°. This is
seen in alkynes and nitriles .


Question 7
Which of the following best describes a pi (π) bond?
A) Formed by end-to-end overlap of orbitals along the bond axis
B) Formed by side-to-side overlap of p orbitals
C) Stronger than a sigma bond
D) Present in all single bonds

Correct Answer: B

Rationale: Pi bonds are formed by side-to-side overlap of unhybridized p orbitals
perpendicular to the bond axis. They are weaker than sigma bonds .


Question 8
What is the formal charge on the nitrogen in ammonium ion (NH₄⁺)?
A) -1
B) 0
C) +1
D) +2

Correct Answer: C

Rationale: For NH₄⁺, nitrogen has 5 valence electrons, 0 non-bonding electrons, and 4
bonding electrons (½ of 8). FC = 5 - (0 + 4) = +1 .

, Question 9
Which molecule exhibits resonance?
A) CH₄
B) CH₃CH₃
C) Benzene (C₆H₆)
D) Cyclohexane

Correct Answer: C

Rationale: Benzene exhibits resonance due to delocalized π electrons in the aromatic
ring. The actual structure is a resonance hybrid of two equivalent contributing
structures .


Question 10
Electronegativity generally increases:
A) Down a group, left to right across a period
B) Up a group, right to left across a period
C) Up a group, left to right across a period
D) Down a group, right to left across a period

Correct Answer: C

Rationale: Electronegativity increases going up a group (smaller atoms) and left to right
across a period (more protons, less shielding) .


Question 11
Which of the following electron configurations represents the magnesium cation (Mg²⁺)?
A) 1s²2s²2p⁶3s²3p²
B) 1s²2s²2p⁶
C) 1s²2s²2p⁴
D) 1s²2s²2p⁶3s²

Correct Answer: B

Rationale: Magnesium (Mg) has electron configuration 1s²2s²2p⁶3s². Mg²⁺ loses two
electrons from the 3s orbital to achieve a stable octet .