DAT General Chemistry: Atomic Structure and Periodic Trends 1 — Questions and Answers
Question 1: What is the maximum number of electrons that can occupy the third principal energy level (n = 3)?
- 8
- 18 (Correct answer)
- 32
- 6
Correct answer: 18
The maximum number of electrons in principal energy level n is given by 2n², so for n = 3: 2(3²) = 18 electrons.
Question 2: Which element has the ground-state electron configuration [Ne]3s²3p⁴?
- Carbon
- Sulfur (Correct answer)
- Oxygen
- Silicon
Correct answer: Sulfur
[Ne]3s²3p⁴ represents 16 total electrons (10 from Ne core + 6 valence), which corresponds to sulfur (Z = 16).
Question 3: According to the Aufbau principle, which subshell is filled immediately before the 4s subshell?
- 3d
- 3p (Correct answer)
- 4p
- 4d
Correct answer: 3p
The Aufbau filling order proceeds as 1s, 2s, 2p, 3s, 3p, 4s — so 3p fills directly before 4s.
Question 4: What is the wavelength of light with a frequency of 6.0 × 10¹⁴ Hz? (c = 3.0 × 10⁸ m/s)
- 5.0 × 10⁻⁷ m (Correct answer)
- 2.0 × 10⁶ m
- 1.8 × 10²³ m
- 5.0 × 10⁻¹ m
Correct answer: 5.0 × 10⁻⁷ m
Using λ = c/f: (3.0 × 10⁸ m/s) ÷ (6.0 × 10¹⁴ Hz) = 5.0 × 10⁻⁷ m, which falls in the visible light range.
Question 5: Which quantum number determines the shape of an atomic orbital?
- Principal quantum number (n)
- Angular momentum quantum number (l) (Correct answer)
- Magnetic quantum number (mₗ)
- Spin quantum number (mₛ)
Correct answer: Angular momentum quantum number (l)
The angular momentum quantum number (l) defines orbital shape: l = 0 (s), l = 1 (p), l = 2 (d), l = 3 (f).
Question 6: Iron has atomic number 26. In which period and group of the periodic table does it appear?
- Group 6, Period 4
- Group 8, Period 4 (Correct answer)
- Group 6, Period 3
- Group 8, Period 3
Correct answer: Group 8, Period 4
Iron (Z = 26) has configuration [Ar]3d⁶4s², placing it in Period 4 and Group 8 as a d-block (transition) element.
Question 7: Which of the following Period 3 elements has the largest atomic radius?
- Na (Correct answer)
- Mg
- Al
- Si
Correct answer: Na
Atomic radius decreases across a period due to increasing nuclear charge, so Na (leftmost of the group) has the largest atomic radius.
DAT General Chemistry: Atomic Structure and Periodic Trends 1
What is the maximum number of electrons that can occupy the third principal energy level (n = 3)?