Rucete ✏ AP Chemistry In a Nutshell
1. Structure of the Atom
Practice Questions
This chapter introduces the fundamental structure of the atom, including the historical discoveries of subatomic particles, the development of atomic models from Dalton to Schrödinger, and the principles of electron configuration, quantum numbers, and orbital theory.
(Multiple Choice — Click to Reveal Answer)
1. Albert Einstein received the Nobel Prize for which phenomenon?
(A) It is spectroscopy using visible light.
(B) It is the ejection of electrons from a surface by photons.
(C) It measures E = mc² for any element.
(D) It is another way of stating the Heisenberg uncertainty principle.
Answer
(B) — The photoelectric effect is the ejection of an electron from a surface by photons.
2. The wave-particle duality of nature applies to:
(A) everything
(B) light only
(C) gamma rays only
(D) electrons only
Answer
(A) — Wave-particle duality applies to all matter, including photons and electrons.
3. Calcium can have an electron in an f orbital:
(A) in the elemental state
(B) in an excited state
(C) as a positive ion
(D) as a negative ion
Answer
(B) — Only in excited states do calcium electrons occupy higher orbitals like f.
4. What is the complete electron configuration for silicon?
(A) [Ne] 3s² 3p²
(B) 1s² 2s² 2p⁶ 3s² 3p⁴
(C) 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁴
(D) 1s² 2s² 2p⁶ 3s² 3p²
Answer
(D) — This is the full electron configuration of Si (atomic number 14).
5. Which wave has the highest energy?
(A) Wave A
(B) Wave B
(C) Wave C
(D) Wave D
Answer
(C) — The wave with the highest frequency corresponds to the highest energy.
6. What is the wavelength of light with a frequency of 4.00 × 10¹⁴ s⁻¹?
(A) 7.5 nm
(B) 1,333 nm
(C) 750. nm
(D) 1.33 cm⁻¹
Answer
(C) — λ = c/ν = 3.00 × 10⁸ m/s ÷ 4.00 × 10¹⁴ s⁻¹ = 750 nm
7. Which element has the greatest number of p electrons?
(A) Arsenic
(B) Silicon
(C) Iron
(D) Chlorine
Answer
(A) — Arsenic has 15 p electrons (Periods 2, 3, and 4 combined).
8. What is the maximum number of valence electrons any atom may have?
(A) 32
(B) 2
(C) 14
(D) 8
Answer
(D) — 2 s electrons + 6 p electrons = max 8 valence electrons.
9. Which experiment determined the charge of the electron?
(A) Gold foil
(B) Cathode ray
(C) Oil drop
(D) Mass spectrometer
Answer
(C) — Millikan’s oil drop experiment determined the electron’s charge.
10. What does Dalton’s atomic theory claim?
(A) All atoms are identical in mass and properties
(B) Atoms split during chemical reactions
(C) Atoms have internal structure
(D) Isotopes are considered in all atoms
Answer
(A) — Dalton’s theory proposed atoms of an element are identical.
11. Which region of the periodic table contains elements with d electrons listed last in their configuration?
(A) Group 1A
(B) Group 2A
(C) Transition metals
(D) Noble gases
Answer
(C) — Transition metals are characterized by d electrons in their outermost configurations.
12. How many protons, neutrons, and electrons are in a neutral atom of chromium-52?
(A) 52 p, 28 n, 52 e⁻
(B) 28 p, 24 n, 24 e⁻
(C) 26 p, 26 n, 26 e⁻
(D) 24 p, 28 n, 24 e⁻
Answer
(D) — Atomic number of Cr is 24, mass number is 52 → 28 neutrons (52–24), 24 protons, and 24 electrons.
13. Which element has the largest number of unpaired electrons?
(A) Fe
(B) Al
(C) Ag
(D) Ni
Answer
(A) — Fe (iron) has 4 unpaired d electrons in its ground state.
14. Which configuration corresponds to a noble gas?
(A) 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹
(B) 1s² 2s² 2p⁶ 3s² 3p⁴
(C) 1s² 2s² 2p⁶ 3s² 3p⁶
(D) 1s² 2s² 2p⁶ 3s¹
Answer
(C) — Ends in ns² np⁶, typical configuration of noble gases like argon.
15. Which electron transition absorbs the most energy?
(A) n = 1 to n = 3
(B) n = 5 to n = 2
(C) n = 2 to n = 3
(D) n = 4 to n = 1
Answer
(A) — The largest energy input is needed to move from n = 1 to n = 3.
16. Which quantum number defines orbital shape?
(A) n
(B) ℓ
(C) mℓ
(D) ms
Answer
(B) — ℓ (azimuthal quantum number) defines the orbital shape (s, p, d, f).
17. Which experiment was used to find the charge of an electron?
(A) Gold foil experiment
(B) Cathode ray experiment
(C) Oil drop experiment
(D) Mass spectrometer
Answer
(C) — The Millikan oil drop experiment determined the electron’s charge.
18. Which is NOT part of Dalton’s atomic theory?
(A) Atoms rearrange in chemical reactions
(B) Atoms follow the law of multiple proportions
(C) All atoms of an element are identical
(D) Atoms are divisible
Answer
(D) — Dalton proposed atoms were indivisible; this was later disproved.
19. Which statement is correct?
(A) Technetium has 15 p electrons
(B) Argon has 18 valence electrons
(C) Oxygen has 4 electrons
(D) Tungsten has 14 f electrons
Answer
(D) — Tungsten follows the lanthanide series and includes 14 f electrons.
20. Which quantum number describes orbital shape?
(A) n
(B) ℓ
(C) mℓ
(D) ms
Answer
(B) — ℓ describes the orbital's shape: s (0), p (1), d (2), f (3).
21. What is the common factor in these masses: 4.72 × 10⁻³⁴ g, 9.44 × 10⁻³⁴ g, 1.18 × 10⁻³³ g, 1.65 × 10⁻³³ g?
(A) 1.18 × 10⁻³⁴ g
(B) 2.36 × 10⁻³⁴ g
(C) 4.72 × 10⁻³⁴ g
(D) 9.44 × 10⁻³⁴ g
Answer
(B) — 2.36 × 10⁻³⁴ g is the largest common divisor.
22. Which is FALSE?
(A) 4d orbitals are in the 4th period
(B) 7s orbitals are in the 7th period
(C) 4f orbitals are in the 6th period
(D) 6s orbitals are spherical
Answer
(A) — 4d orbitals appear in the 5th period, not the 4th.
23. How many electrons can an f sublevel hold?
(A) 14
(B) 10
(C) 6
(D) 2
Answer
(A) — f sublevel has 7 orbitals × 2 electrons each = 14.
24. Valence electrons are:
(A) all electrons beyond noble gas core
(B) all outermost sublevel electrons
(C) s and p electrons in the highest shell
(D) electrons in the last unfilled sublevel
Answer
(C) — Valence electrons include outermost s and p electrons only.
25. What equation defines the energy of a photon?
(A) —
(B) E = mc²
(C) E = IR
(D) E = hν
Answer
(D) — The energy of a photon is given by Planck’s formula: E = hν.
26. Which of the following sets of quantum numbers is invalid?
(A) n = 3, ℓ = 2, mℓ = 2, ms = +½
(B) n = 2, ℓ = 2, mℓ = 1, ms = –½
(C) n = 4, ℓ = 1, mℓ = –1, ms = +½
(D) n = 5, ℓ = 0, mℓ = 0, ms = –½
Answer
(B) — ℓ must be less than n. ℓ = 2 is not allowed when n = 2.
27. Which element is likely to have the electron configuration [Kr] 5s¹ 4d⁵?
(A) Molybdenum (Mo)
(B) Technetium (Tc)
(C) Niobium (Nb)
(D) Ruthenium (Ru)
Answer
(A) — Mo is an exception to the Aufbau rule, favoring half-filled d orbitals.
28. What is the significance of Heisenberg’s uncertainty principle in atomic theory?
(A) It predicts the exact position of electrons
(B) It describes the shape of orbitals
(C) It states electrons behave as both waves and particles
(D) It limits how precisely we can know an electron’s position and momentum
Answer
(D) — Heisenberg’s principle says we cannot know both position and momentum precisely.
29. Which type of electromagnetic radiation has the shortest wavelength?
(A) Infrared
(B) Ultraviolet
(C) Gamma rays
(D) Microwaves
Answer
(C) — Gamma rays have the highest energy and the shortest wavelength.
30. Which statement about electron energy levels is correct?
(A) Electrons absorb energy when dropping to lower levels
(B) The energy difference between levels increases as n increases
(C) Electrons release energy as they move to higher levels
(D) Light is emitted when an electron drops to a lower energy level
Answer
(D) — Electrons emit photons when moving to lower energy states.
31. Which orbital diagram correctly follows Hund’s rule for nitrogen (atomic number 7)?
(A) All 2p electrons paired
(B) 2p orbitals each with 1 electron of same spin
(C) 2p orbitals filled left to right with opposite spins
(D) One 2p orbital empty, others full
Answer
(B) — Hund’s rule states each orbital in a sublevel must have one electron before any are paired.
32. What is the principal quantum number of the outermost electron in barium (Ba)?
(A) 4
(B) 5
(C) 6
(D) 7
Answer
(C) — Barium is in Period 6; outermost electrons are in the 6s sublevel.
33. Which element has the configuration ending in 3p⁵?
(A) Sodium (Na)
(B) Phosphorus (P)
(C) Chlorine (Cl)
(D) Sulfur (S)
Answer
(C) — Chlorine ends in 3p⁵, with 7 valence electrons in total.
34. Which orbital is first to be filled in the third energy level?
(A) 3p
(B) 3d
(C) 3s
(D) 2p
Answer
(C) — 3s is the first sublevel filled in the third principal energy level.
35. Why are valence electrons important in chemistry?
(A) They determine nuclear stability
(B) They affect isotopic mass
(C) They dictate reactivity and bonding behavior
(D) They determine orbital shapes
Answer
(C) — Valence electrons are the outermost electrons and are responsible for chemical reactivity.
36. Describe the major result of Rutherford’s gold foil experiment and its impact on atomic structure.
Answer
It showed that atoms have a small, dense, positively charged nucleus, disproving the plum pudding model.
37. What is the maximum number of electrons that can occupy the third principal energy level?
Answer
18 electrons — calculated using the formula 2n² where n = 3 → 2(3²) = 18
38. State the Pauli exclusion principle in the context of atomic orbitals.
Answer
No two electrons in an atom can have the same set of four quantum numbers.
39. Explain how energy is emitted or absorbed when an electron transitions between energy levels.
Answer
Energy is emitted when electrons drop to lower levels and absorbed when they move to higher levels.
40. Define the four quantum numbers used to describe the properties of electrons.
Answer
n = energy level; ℓ = orbital shape; mℓ = orbital orientation; ms = spin (+½ or –½).
41. Why is the 4s orbital filled before the 3d orbital?
Answer
Because 4s has lower energy than 3d based on the Aufbau principle.
42. How does Hund’s rule affect the filling of p orbitals?
Answer
Each p orbital gets one electron before any are paired, maximizing unpaired electrons.
43. How many orbitals are in the d sublevel, and how many electrons can it hold?
Answer
5 orbitals; each can hold 2 electrons → 10 electrons total.
44. Write the complete electron configuration for the phosphorus atom (atomic number 15).
Answer
1s² 2s² 2p⁶ 3s² 3p³
45. What is the wavelength of light with frequency 6.00 × 10¹⁴ Hz? (c = 3.00 × 10⁸ m/s)
Answer
λ = c/ν = (3.00 × 10⁸ m/s) ÷ (6.00 × 10¹⁴ Hz) = 5.00 × 10⁻⁷ m or 500 nm
46. What does the term “ground state” mean in terms of atomic electrons?
Answer
The lowest energy state where all electrons occupy the lowest possible orbitals.
47. How many unpaired electrons are there in an atom of nitrogen (atomic number 7)?
Answer
3 unpaired electrons — in the 2p orbitals.
48. What did Millikan’s oil drop experiment determine about the electron?
Answer
It measured the exact charge of a single electron: –1.60 × 10⁻¹⁹ coulombs.
49. Identify the quantum numbers for the last electron added to a calcium atom (atomic number 20).
Answer
n = 4, ℓ = 0, mℓ = 0, ms = +½ — corresponds to the 4s¹ or 4s² electron.
50. Explain how de Broglie’s hypothesis supports the wave-particle duality of electrons.
Answer
He proposed that particles like electrons can exhibit wave properties, with wavelength λ = h/mv.