40 exam-style questions on Chemistry · Atomic structure, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.
Ten Chemistry · Atomic structure questions with answers
Try each one, then open the answer. These ten stay the same; the test draws new ones every time.
1. Using 1/λ = RH(1/n12 − 1/n22), what is the ratio of the wavelength of the first (longest-wavelength) Lyman line to that of the first Balmer line of hydrogen?
A
5 : 27
B
27 : 5
C
1 : 4
D
4 : 1
Show answer
Answer: A. First Lyman line (n = 2 → 1): 1/λ = RH(1 − 1/4) = 3RH/4; first Balmer line (n = 3 → 2): 1/λ = RH(1/4 − 1/9) = 5RH/36. The wavelengths are the reciprocals, so λLyman : λBalmer = 4/3 : 36/5 = 5 : 27. 27 : 5 compares the wave numbers instead, and 1 : 4 is the ratio of the two series limits.
2. Which two elements of the first transition series (scandium to zinc) have ground-state configurations that do not follow the expected filling order?
A
scandium and zinc
B
chromium and copper
C
iron and nickel
D
manganese and cobalt
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Answer: B. Chromium is [Ar] 3d5 4s1, not 3d4 4s2, and copper is [Ar] 3d10 4s1, not 3d9 4s2, because half-filled and completely filled d subshells are extra stable. Scandium and zinc follow the normal order.
3. Which statement comparing a proton with an electron is correct?
A
equal charge, opposite sign; electron about 1836 times heavier
B
equal mass, opposite sign; proton charge 1836 times larger
C
proton charge twice as large; proton about 1836 times heavier
D
equal charge, opposite sign; proton about 1836 times heavier
Show answer
Answer: D. The proton and the electron carry charges of the same size, 1.602 × 10−19 C, with opposite signs, but the proton (1.673 × 10−27 kg) is about 1836 times as heavy as the electron (9.11 × 10−31 kg). The neutron is slightly heavier than the proton and has no charge.
4. The covalent radius of a chlorine atom is 99 pm. What is this in angstroms?
A
9.9 Å
B
0.099 Å
C
99 Å
D
0.99 Å
Show answer
Answer: D. 1 Å = 10−10 m and 1 pm = 10−12 m, so 1 Å = 100 pm and 99 pm = 0.99 Å (9.9 × 10−11 m). 9.9 Å divides by 10 instead of 100, and 0.099 Å divides by 1000.
5. An atom X has mass number 37 and contains 20 neutrons. How many electrons are present in the ion X−?
A
17
B
21
C
16
D
18
Show answer
Answer: D. Z = 37 − 20 = 17, so the neutral atom has 17 electrons; the 1− ion has gained one, giving 18. 16 removes an electron instead of adding one.
6. The wave-mechanical (Schrödinger) model of the atom differs from Bohr's model mainly because it
A
places electrons in fixed circular orbits of definite radius
B
gives the probability of finding the electron, not its path
C
treats the electron as a particle and never as a wave
D
allows an electron in an atom to have any amount of energy
Show answer
Answer: B. Schrödinger treated the electron as a wave and obtained orbitals: regions where the probability of finding the electron is high, with no exact path. Fixed circular orbits belong to Bohr's model, and both models allow only certain (quantised) energies.
7. An orbital with azimuthal quantum number l = 1 is
A
an s orbital, which is spherical
B
a p orbital, which is dumbbell-shaped
C
a d orbital, which is dumbbell-shaped
D
a p orbital, which is spherical
Show answer
Answer: B. l = 0, 1, 2 and 3 correspond to s, p, d and f subshells. l = 1 is a p orbital, which has two lobes on opposite sides of the nucleus (dumbbell shape); s orbitals are the spherical ones.
8. How many neutrons are present in one molecule of heavy water, 2H216O? (atomic numbers: H = 1, O = 8)
A
8
B
12
C
20
D
10
Show answer
Answer: D. Each deuterium atom, 2H, has 1 proton and 1 neutron, and 16O has 8 neutrons: 2 × 1 + 8 = 10. 8 forgets the neutrons in deuterium, 12 counts the whole mass number of each 2H as neutrons, and 20 is the total number of nucleons.
9. Which series of lines in the spectrum of the hydrogen atom lies in the ultraviolet region?
A
Balmer
B
Paschen
C
Brackett
D
Lyman
Show answer
Answer: D. Lyman lines come from electrons falling to n = 1, the largest energy gaps, so they are in the ultraviolet. Balmer lines (to n = 2) are visible; Paschen (to n = 3) and Brackett (to n = 4) are infrared.
10. Which pair of values of n and l is not allowed for an electron in an atom?
A
n = 3, l = 2
B
n = 2, l = 1
C
n = 1, l = 0
D
n = 4, l = 4
Show answer
Answer: D. l can take whole-number values from 0 to n − 1. For n = 4 the largest value is l = 3 (an f subshell), so l = 4 is impossible. The other pairs describe 3d, 2p and 1s subshells.
Chemistry · Atomic structure: questions students ask
How many Chemistry · Atomic structure MCQs are there?
40, each with the answer and a short explanation, across 2 topics: Particles, photons and the Bohr model, Orbitals and electronic configuration. Every chapter test draws ten of them, so you can take it many times.
Is the MDCAT Chemistry chapter 2 test free?
Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.
How is the chapter test marked?
The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.
