Free Practice Quiz Question List

04 Atomic Structure and Isotopes Online Quiz Questions

Use this free practice quiz with 20 questions to review 04 Atomic Structure and Isotopes, test your knowledge, and prepare for your next test or exam.

20 questions

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1 point

Which pair of atoms are isotopes of the same element?

A
Atom P: 8 protons, 8 neutrons; Atom Q: 8 protons, 8 neutrons
B
Atom P: 8 protons, 8 neutrons; Atom Q: 8 protons, 10 neutrons
C
Atom P: 8 protons, 9 neutrons; Atom Q: 9 protons, 10 neutrons
D
Atom P: 8 protons, 8 neutrons; Atom Q: 10 protons, 8 neutrons

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1 point

A neutral atom is written as $^{37}_{17}\mathrm{Cl}$ . Which set gives its numbers of protons, neutrons, and electrons, respectively?

A
17 protons, 37 neutrons, 17 electrons
B
20 protons, 17 neutrons, 20 electrons
C
17 protons, 20 neutrons, 17 electrons
D
37 protons, 17 neutrons, 37 electrons

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1 point

A neutral atom has atomic number $15$ and mass number $31$ . Which particle counts are consistent with those values?

A
15 protons, 16 neutrons, 15 electrons
B
15 protons, 31 neutrons, 15 electrons
C
16 protons, 15 neutrons, 16 electrons
D
31 protons, 15 neutrons, 31 electrons

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1 point

Two atoms have the same atomic number but different mass numbers. Which conclusion follows from the definitions of atomic number and isotope?

A
Atoms with the same mass number must be the same element.
B
Atoms with different neutron counts must be different elements.
C
Atoms with the same number of electrons must be isotopes.
D
Atoms with the same atomic number are the same element, even if their neutron counts differ.

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1 point

An isotope has mass number $A=35$ , but its measured mass is not exactly $35\,\mathrm{u}$ . Which interpretation is consistent with the distinction between mass number and measured isotope mass?

A
The isotope's measured mass must equal its mass number exactly because both count protons and neutrons.
B
Its mass number is a whole-number particle count, while its measured mass can differ from that number.
C
Its mass number is the weighted average of all naturally occurring isotopes.
D
A non-whole-number isotope mass proves the atom contains a fractional number of neutrons.

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1 point

A neutral sodium-23 atom has 11 electrons, and its mass is approximately $23\,\mathrm{u}$ . Using an electron mass of about $\frac{1}{1836}$ of a proton mass and a proton mass close to $1\,\mathrm{u}$ , which is the best estimate of the fraction of the atom's mass contributed by all its electrons?

A
About $0.026$ of the atom's mass
B
About $0.0026$ of the atom's mass
C
About $0.00026$ of the atom's mass
D
About $0.26$ of the atom's mass

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1 point

By definition, what mass does $1\,\mathrm{u}$ represent?

A
$\frac{1}{12}$ of the mass of a carbon-12 atom
B
$\frac{1}{12}\,\mathrm{u}$
C
The mass of one proton exactly
D
The weighted average mass of naturally occurring carbon atoms

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1 point

A carbon sample contains $98.93\%$ carbon-12 with mass $12.0000\,\mathrm{u}$ and $1.07\%$ carbon-13 with mass $13.0034\,\mathrm{u}$ . What is the sample's average atomic mass, rounded to four decimal places?

A
$12.0000\,\mathrm{u}$
B
$12.1070\,\mathrm{u}$
C
$12.9893\,\mathrm{u}$
D
$12.0107\,\mathrm{u}$

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1 point

Cathode rays behaved as negatively charged particles, and their properties were consistent across different electrode materials. Which conclusion is best supported by these observations?

A
Atoms contain no charged particles because the rays passed between the electrodes.
B
Electrons are produced only by the particular metal used as an electrode.
C
Electrons are negatively charged constituents of atoms, so atoms have internal structure.
D
Atoms consist of electrons embedded in a tiny, dense positive nucleus.

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1 point

In a gold-foil experiment, most positively charged alpha particles passed through with little deflection, while a small number deflected sharply, some back toward the source. Which atomic picture best accounts for both observations?

A
A diffuse positive charge fills most of the atom and causes all alpha particles to bend slightly.
B
Most of the atom is open space, with positive charge and most of its mass concentrated in a tiny nucleus.
C
Electrons and protons are distributed uniformly throughout a solid atom.
D
The gold foil's atoms are indivisible spheres that deflect alpha particles equally in all directions.

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1 point

How did the discovery of a neutral nuclear particle with a mass similar to a proton help explain why atoms of the same element can have different masses?

A
A neutron can change the nucleus's mass without changing the proton-defined element identity.
B
An electron can change the element's atomic number while leaving the proton count fixed.
C
A neutron gives the atom a different atomic number while preserving its mass number.
D
The nucleus must contain the same number of protons and neutrons in every isotope.

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1 point

Which statement best distinguishes the modern quantum-mechanical description of electrons from a picture of electrons as tiny planets?

A
Electrons follow fixed circular paths, and spectra show those paths directly.
B
Orbitals are the physical surfaces of electron shells, with electrons fixed on them.
C
The nucleus is replaced by a probability cloud, while electrons remain stationary.
D
Orbitals represent regions where electrons are likely to be found, and the model is supported by measurements such as atomic spectra.

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1 point

A neutral atom is represented by ${}^{23}_{11}\mathrm{Na}$ . Which description gives its numbers of protons, neutrons, and electrons, in that order?

A
11 protons, 12 neutrons, and 11 electrons
B
11 protons, 23 neutrons, and 11 electrons
C
23 protons, 11 neutrons, and 23 electrons
D
11 protons, 12 neutrons, and 12 electrons

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1 point

An atom contains 15 protons, 16 neutrons, and 15 electrons. Which conclusion about where nearly all its mass is concentrated is best supported by the relative particle masses?

A
The electrons, because they occupy the region around the nucleus
B
The electrons and nucleus equally, because the atom is neutral
C
The nucleus, because it contains protons and neutrons, each with a mass close to $1\,\mathrm{u}$
D
The nucleus, because neutrons are much more massive than protons

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1 point

Which pair consists of two isotopes of the same element?

A
Atoms with 8 protons and 8 neutrons, and 10 protons and 8 neutrons
B
Atoms with 8 protons and 8 neutrons, and 8 protons and 10 neutrons
C
Atoms with 8 protons and 8 neutrons, and 10 protons and 10 neutrons
D
Atoms with 8 protons and 8 neutrons, and 8 protons and 8 neutrons

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1 point

A sample contains two isotopes: one has a mass of $10.0\,\mathrm{u}$ and an abundance of $20\%$ ; the other has a mass of $11.0\,\mathrm{u}$ and an abundance of $80\%$ . What is the sample’s average atomic mass?

A
$10.2\,\mathrm{u}$
B
$10.5\,\mathrm{u}$
C
$10.8\,\mathrm{u}$
D
$11.0\,\mathrm{u}$

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1 point

A carbon atom has 6 protons and 7 neutrons, and its measured isotope mass is about $13.0034\,\mathrm{u}$ . Which statement correctly distinguishes its mass number from its measured isotope mass?

A
Its mass number is 13, while its measured mass is not exactly $13\,\mathrm{u}$ .
B
Its mass number is 13.0034 because the mass number is the measured isotope mass.
C
Its mass number is 6 because the atomic number gives the total number of nuclear particles.
D
Its mass number is not defined because the measured mass is not a whole number.

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1 point

In cathode-ray experiments, the rays deflected in electric and magnetic fields, and their properties were consistent across different electrode materials. Which conclusion is best supported by the combination of observations?

A
Atoms are indivisible, because the rays are produced during experiments on matter.
B
The rays are positively charged particles unique to the gold used in the apparatus.
C
Atoms contain diffuse positive charge with electrons embedded in it, as proven directly by the deflection alone.
D
Electrons are constituents of atoms, since the negatively charged particles behaved consistently with different electrode materials.

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1 point

In the gold-foil experiment, most positively charged alpha particles passed through with little deflection, while a small number were sharply deflected, some back toward the source. Which atomic structure best explains both observations?

A
Atoms are solid throughout, but alpha particles usually pass through because their charge is neutralized by gold.
B
Atoms are mostly open space, with positive charge and most mass concentrated in a tiny nucleus.
C
Positive charge and mass are spread uniformly across the atom, causing occasional sharp deflections.
D
The atom’s electrons form a dense central core that repels most alpha particles.

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1 point

Which description matches the modern atomic model and the role of atomic spectra in supporting it?

A
Electrons are described by quantum mechanics, with orbitals representing regions where they are likely to be found; atomic spectra support this model.
B
Electrons travel on tiny fixed planetary paths, and orbitals identify those exact paths.
C
Electrons are embedded in diffuse positive charge, and atomic spectra prove this is the complete modern model.
D
Electrons are absent from the space around the nucleus; spectra instead show that atoms are mostly open space.