CHY 142 Exam 1 Practice Exam
1. What is the formal charge on the nitrogen atom in NH₄⁺?
A. −1
B. 0
C. +1
D. +2
Rationale: Nitrogen has 5 valence electrons. In NH₄⁺, it has 4 bonds (8
bonding electrons) and 0 lone pairs. FC = 5 − 0 − ½(8) = +1.
2. What is the formal charge on the oxygen atom in H₃O⁺?
A. −1
B. 0
C. +1
D. +2
Rationale: Oxygen has 6 valence electrons. In H₃O⁺, it has 3 bonds and 1
lone pair. FC = 6 − 2 − ½(6) = +1.
3. What is the formal charge on the carbon atom in CH₃⁻?
A. −1
B. 0
C. +1
D. +2
Rationale: Carbon has 4 valence electrons. In CH₃⁻, it has 3 bonds and 1
lone pair. FC = 4 − 2 − ½(6) = −1.
4. What is the electron-domain geometry for a central atom with 4 electron
domains?
A. Trigonal planar
B. Tetrahedral
, C. Trigonal bipyramidal
D. Octahedral
Rationale: Four electron domains (bonds or lone pairs) arrange
themselves in a tetrahedral geometry to minimize repulsion.
5. What is the molecular geometry for a central atom with 3 bonding pairs and
1 lone pair?
A. Tetrahedral
B. Trigonal pyramidal
C. Bent
D. Linear
Rationale: The electron-domain geometry is tetrahedral, but the lone pair
makes the molecular geometry trigonal pyramidal (e.g., NH₃).
6. What is the molecular geometry for a central atom with 2 bonding pairs and
2 lone pairs?
A. Linear
B. Trigonal planar
C. Bent
D. Tetrahedral
Rationale: The electron-domain geometry is tetrahedral, but with two
lone pairs the molecular geometry is bent (e.g., H₂O).
7. What is the approximate bond angle in a tetrahedral geometry?
A. 90°
B. 120°
C. 109.5°
D. 180°
Rationale: Tetrahedral geometry has bond angles of approximately
109.5°.
8. What is the approximate bond angle in a trigonal planar geometry?
A. 90°
B. 120°
C. 109.5°
, D. 180°
Rationale: Trigonal planar geometry has bond angles of approximately
120°.
9. Which bond is shorter: a C–C single bond or a C=C double bond?
A. C–C single bond
B. C=C double bond
C. They are equal
D. Cannot be determined
Rationale: Double bonds have greater electron density between nuclei,
pulling atoms closer, so C=C is shorter than C–C.
10.What is the general structure of an aldehyde?
A. R–OH
B. R–O–R′
C. R–CHO
D. R–COOH
Rationale: An aldehyde has a carbonyl group (C=O) bonded to at least one
hydrogen atom (R–CHO).
11.What is the general structure of a ketone?
A. R–CHO
B. R₂C=O
C. R–COOH
D. R–COOR′
Rationale: A ketone has a carbonyl group bonded to two carbon-
containing groups (R₂C=O).
12.What is the general structure of a carboxylic acid?
A. R–CHO
B. R₂C=O
C. R–COOH
D. R–OH
Rationale: A carboxylic acid contains a carbonyl group bonded to a
hydroxyl group (R–COOH).
1. What is the formal charge on the nitrogen atom in NH₄⁺?
A. −1
B. 0
C. +1
D. +2
Rationale: Nitrogen has 5 valence electrons. In NH₄⁺, it has 4 bonds (8
bonding electrons) and 0 lone pairs. FC = 5 − 0 − ½(8) = +1.
2. What is the formal charge on the oxygen atom in H₃O⁺?
A. −1
B. 0
C. +1
D. +2
Rationale: Oxygen has 6 valence electrons. In H₃O⁺, it has 3 bonds and 1
lone pair. FC = 6 − 2 − ½(6) = +1.
3. What is the formal charge on the carbon atom in CH₃⁻?
A. −1
B. 0
C. +1
D. +2
Rationale: Carbon has 4 valence electrons. In CH₃⁻, it has 3 bonds and 1
lone pair. FC = 4 − 2 − ½(6) = −1.
4. What is the electron-domain geometry for a central atom with 4 electron
domains?
A. Trigonal planar
B. Tetrahedral
, C. Trigonal bipyramidal
D. Octahedral
Rationale: Four electron domains (bonds or lone pairs) arrange
themselves in a tetrahedral geometry to minimize repulsion.
5. What is the molecular geometry for a central atom with 3 bonding pairs and
1 lone pair?
A. Tetrahedral
B. Trigonal pyramidal
C. Bent
D. Linear
Rationale: The electron-domain geometry is tetrahedral, but the lone pair
makes the molecular geometry trigonal pyramidal (e.g., NH₃).
6. What is the molecular geometry for a central atom with 2 bonding pairs and
2 lone pairs?
A. Linear
B. Trigonal planar
C. Bent
D. Tetrahedral
Rationale: The electron-domain geometry is tetrahedral, but with two
lone pairs the molecular geometry is bent (e.g., H₂O).
7. What is the approximate bond angle in a tetrahedral geometry?
A. 90°
B. 120°
C. 109.5°
D. 180°
Rationale: Tetrahedral geometry has bond angles of approximately
109.5°.
8. What is the approximate bond angle in a trigonal planar geometry?
A. 90°
B. 120°
C. 109.5°
, D. 180°
Rationale: Trigonal planar geometry has bond angles of approximately
120°.
9. Which bond is shorter: a C–C single bond or a C=C double bond?
A. C–C single bond
B. C=C double bond
C. They are equal
D. Cannot be determined
Rationale: Double bonds have greater electron density between nuclei,
pulling atoms closer, so C=C is shorter than C–C.
10.What is the general structure of an aldehyde?
A. R–OH
B. R–O–R′
C. R–CHO
D. R–COOH
Rationale: An aldehyde has a carbonyl group (C=O) bonded to at least one
hydrogen atom (R–CHO).
11.What is the general structure of a ketone?
A. R–CHO
B. R₂C=O
C. R–COOH
D. R–COOR′
Rationale: A ketone has a carbonyl group bonded to two carbon-
containing groups (R₂C=O).
12.What is the general structure of a carboxylic acid?
A. R–CHO
B. R₂C=O
C. R–COOH
D. R–OH
Rationale: A carboxylic acid contains a carbonyl group bonded to a
hydroxyl group (R–COOH).
