Rucete ✏ AP Chemistry In a Nutshell
1. Structure of the Atom — Practice Questions 2
This chapter explores atomic structure with a fresh set of problems, emphasizing the quantum mechanical model, electron behavior, and the experiments that shaped our modern understanding of the atom. These questions aim to test deeper conceptual understanding and application skills.
(Multiple Choice — Click to Reveal Answer)
1. Which scientist is credited with discovering the neutron?
(A) Thomson
(B) Rutherford
(C) Millikan
(D) Chadwick
Answer
(D) — James Chadwick discovered the neutron in 1932.
2. What is the charge on a proton?
(A) –1
(B) 0
(C) +1
(D) +2
Answer
(C) — A proton carries a +1 charge.
3. Which particle has the smallest mass?
(A) Proton
(B) Neutron
(C) Electron
(D) Alpha particle
Answer
(C) — Electrons are approximately 1/1836 the mass of protons.
4. Which part of the atom is positively charged?
(A) Electron cloud
(B) Nucleus
(C) Orbital
(D) Neutron
Answer
(B) — The nucleus contains protons and has a positive charge.
5. What is the relative mass of a neutron?
(A) 0
(B) 1
(C) 2
(D) 1836
Answer
(B) — Neutrons have a relative mass of 1.
6. Which of the following particles is found outside the nucleus?
(A) Proton
(B) Neutron
(C) Electron
(D) Alpha particle
Answer
(C) — Electrons are located in orbitals outside the nucleus.
7. Who proposed that electrons occupy specific energy levels around the nucleus?
(A) Bohr
(B) Dalton
(C) Rutherford
(D) Heisenberg
Answer
(A) — Niels Bohr proposed quantized orbits for electrons in the hydrogen atom.
8. Which instrument is used to measure the emission spectrum of elements?
(A) Calorimeter
(B) Spectroscope
(C) Electron microscope
(D) Geiger counter
Answer
(B) — A spectroscope is used to view line spectra emitted by excited atoms.
9. What happens when an electron drops from a higher to a lower energy level?
(A) Energy is absorbed
(B) The atom becomes an isotope
(C) Light is emitted
(D) The nucleus splits
Answer
(C) — The electron releases energy as light when it transitions to a lower energy level.
10. Which color of visible light has the highest energy?
(A) Red
(B) Green
(C) Yellow
(D) Violet
Answer
(D) — Violet light has the highest frequency and thus the most energy.
11. Which of the following is not part of Dalton’s atomic theory?
(A) All matter is composed of atoms
(B) Atoms can be divided into protons, neutrons, and electrons
(C) Atoms of the same element are identical
(D) Atoms combine in whole-number ratios
Answer
(B) — Dalton believed atoms were indivisible; subatomic particles were discovered later.
12. Which subatomic particle is responsible for chemical bonding?
(A) Neutron
(B) Proton
(C) Electron
(D) Nucleon
Answer
(C) — Valence electrons are involved in chemical bonds.
13. What shape is an s orbital?
(A) Dumbbell
(B) Cloverleaf
(C) Sphere
(D) Complex
Answer
(C) — s orbitals are spherical in shape.
14. Which principle states that no two electrons can have the same four quantum numbers?
(A) Hund’s Rule
(B) Pauli Exclusion Principle
(C) Aufbau Principle
(D) Dalton’s Law
Answer
(B) — The Pauli Exclusion Principle ensures unique electron configurations.
15. What is the speed of light in vacuum?
(A) 3.00 × 10⁸ m/s
(B) 1.60 × 10⁻¹⁹ C
(C) 6.02 × 10²³ mol⁻¹
(D) 9.11 × 10⁻³¹ kg
Answer
(A) — The speed of light is 3.00 × 10⁸ meters per second.
16. What is the maximum number of electrons in the second energy level?
(A) 2
(B) 4
(C) 8
(D) 18
Answer
(C) — The second energy level has 1 s orbital and 3 p orbitals, allowing a total of 8 electrons.
17. What does the magnetic quantum number (mℓ) indicate?
(A) Energy level
(B) Orbital shape
(C) Orbital orientation
(D) Electron spin
Answer
(C) — mℓ describes the orientation of the orbital in space.
18. Which value of ℓ corresponds to a d orbital?
(A) 0
(B) 1
(C) 2
(D) 3
Answer
(C) — ℓ = 2 corresponds to d orbitals.
19. Which term describes atoms of the same element with different numbers of neutrons?
(A) Isotopes
(B) Ions
(C) Isomers
(D) Allotropes
Answer
(A) — Isotopes differ in neutron number but have the same atomic number.
20. What is the charge of an alpha particle?
(A) 0
(B) +1
(C) +2
(D) –1
Answer
(C) — Alpha particles are helium nuclei (2 protons), thus +2 charge.
21. Which scientist performed the gold foil experiment?
(A) Bohr
(B) Thomson
(C) Rutherford
(D) Millikan
Answer
(C) — Rutherford’s gold foil experiment led to the discovery of the nucleus.
22. Which subatomic particle has no charge?
(A) Proton
(B) Neutron
(C) Electron
(D) Positron
Answer
(B) — Neutrons are electrically neutral.
23. What is the unit for frequency in the electromagnetic spectrum?
(A) Watts
(B) Hertz
(C) Meters
(D) Joules
Answer
(B) — Frequency is measured in Hertz (Hz), or s⁻¹.
24. What happens to the energy of light as its wavelength decreases?
(A) It increases
(B) It decreases
(C) It stays the same
(D) It becomes zero
Answer
(A) — Shorter wavelength = higher frequency = higher energy.
25. Which equation relates energy and frequency of light?
(A) E = mc²
(B) E = hν
(C) F = ma
(D) V = IR
Answer
(B) — E = hν (Planck’s equation) relates photon energy to frequency.
26. Which quantum number determines the number of sublevels in a principal energy level?
(A) n
(B) ℓ
(C) mℓ
(D) ms
Answer
(A) — The principal quantum number (n) determines the number of sublevels (equal to n).
27. What is the total number of orbitals in the n = 3 energy level?
(A) 3
(B) 6
(C) 9
(D) 18
Answer
(C) — At n = 3, sublevels are 3s (1), 3p (3), and 3d (5): total = 9 orbitals.
28. Which orbital diagram violates Hund’s Rule?
(A) ↑ _ ↑ _ _
(B) ↑↓ _ _ _
(C) ↑ _ _ _ _
(D) ↑ _ ↑ _ ↑
Answer
(B) — In (B), two electrons are paired before each orbital is singly filled.
29. What causes the emission lines in a hydrogen emission spectrum?
(A) Electrons absorbing energy and jumping to higher levels
(B) Electrons moving randomly
(C) Electrons dropping to lower energy levels
(D) Protons decaying into neutrons
Answer
(C) — Light is emitted when electrons fall from higher to lower energy levels.
30. Which electron transition emits the photon with the longest wavelength?
(A) n = 4 → n = 3
(B) n = 3 → n = 1
(C) n = 5 → n = 2
(D) n = 2 → n = 1
Answer
(A) — The smaller the energy change, the longer the wavelength.
31. What is the frequency of light with a wavelength of 600 nm? (c = 3.00 × 10⁸ m/s)
(A) 5.00 × 10¹⁴ Hz
(B) 2.00 × 10⁻⁷ Hz
(C) 1.80 × 10¹⁵ Hz
(D) 3.00 × 10⁻¹² Hz
Answer
(A) — ν = c/λ = (3.00 × 10⁸ m/s) ÷ (6.00 × 10⁻⁷ m) = 5.00 × 10¹⁴ Hz
32. Which statement about the Bohr model is incorrect?
(A) Electrons orbit the nucleus in fixed paths
(B) Energy is quantized
(C) It works well for all atoms
(D) It introduced energy levels
Answer
(C) — The Bohr model works only accurately for hydrogen-like atoms.
33. Which equation relates wavelength to mass and velocity?
(A) E = hν
(B) λ = h/mv
(C) E = mc²
(D) λ = c/ν
Answer
(B) — This is the de Broglie equation for matter waves.
34. Which sublevel first appears in the fourth energy level?
(A) 3d
(B) 4s
(C) 4f
(D) 4p
Answer
(B) — 4s is the first orbital in the 4th energy level (lower in energy than 3d).
35. Which of the following sets of quantum numbers is not allowed?
(A) n = 2, ℓ = 1, mℓ = 0, ms = –½
(B) n = 3, ℓ = 2, mℓ = 2, ms = +½
(C) n = 1, ℓ = 1, mℓ = 0, ms = –½
(D) n = 4, ℓ = 3, mℓ = –2, ms = +½
Answer
(C) — ℓ cannot be ≥ n; when n = 1, ℓ must be 0. ℓ = 1 is invalid here.
36. State one limitation of the Bohr model and explain how the wave-mechanical model addresses it.
Answer
The Bohr model only works for hydrogen-like atoms. The wave-mechanical model uses orbitals and probability to describe electron locations in all atoms.
37. What is meant by an orbital in the context of quantum mechanics?
Answer
An orbital is a region in space where there is a high probability of finding an electron.
38. Why do electrons fill the 4s orbital before the 3d orbital?
Answer
According to the Aufbau principle, 4s is lower in energy than 3d, so it fills first.
39. Define the term “quantum” as it relates to electron energy levels.
Answer
A quantum is a discrete packet of energy associated with electron transitions between energy levels.
40. What evidence supports the idea that electrons have wave-like properties?
Answer
Electron diffraction and interference patterns support the wave nature of electrons, as shown in the double-slit experiment.
41. What is the value of Planck’s constant and its units?
Answer
6.63 × 10⁻³⁴ J·s (joule-seconds)
42. Explain the difference between ground state and excited state.
Answer
Ground state is the lowest energy configuration of electrons; excited state occurs when electrons occupy higher energy levels after absorbing energy.
43. Describe the role of each of the four quantum numbers (n, ℓ, mℓ, ms).
Answer
n: energy level; ℓ: orbital shape; mℓ: orbital orientation; ms: spin direction.
44. Why can no two electrons in an atom have the same set of quantum numbers?
Answer
Due to the Pauli exclusion principle, each electron in an atom must have a unique set of four quantum numbers.
45. Calculate the energy of a photon with frequency 5.00 × 10¹⁴ Hz. (h = 6.63 × 10⁻³⁴ J·s)
Answer
E = hν = (6.63 × 10⁻³⁴)(5.00 × 10¹⁴) = 3.32 × 10⁻¹⁹ J
46. What does the Heisenberg uncertainty principle state?
Answer
It states that the position and momentum of a particle cannot both be known exactly at the same time.
47. Why are orbitals sometimes shown as boxes in diagrams?
Answer
Boxes represent individual orbitals where each can hold up to two electrons with opposite spins.
48. What determines the shape of an orbital?
Answer
The azimuthal quantum number (ℓ) determines orbital shape (s: sphere, p: dumbbell, d/f: complex).
49. How does the periodic table reflect electron configurations?
Answer
The periodic table is arranged so that element position reflects its valence electron configuration and sublevel filling (s, p, d, f blocks).
50. Give an example of an element with an electron configuration that is an exception to the Aufbau principle and explain why.
Answer
Chromium: [Ar] 4s¹ 3d⁵ — Half-filled d sublevels are more stable, so an electron shifts from 4s to 3d.