04 Atomic Structure and Isotopes Online Quiz Questions

A neutral atom contains 15 protons, 16 neutrons, and 15 electrons. Explain its net charge and where nearly all its mass is concentrated, then estimate its mass in unified atomic mass units (u).

For a neutral atom written as $^{23}_{11}\mathrm{Na}$, determine the numbers of protons, neutrons, and electrons. Explain how the notation and the word “neutral” support your counts.

Compare $^{12}_{6}\mathrm{C}$ and $^{13}_{6}\mathrm{C}$. Explain why they are atoms of the same element but different isotopes, and identify the particle-count difference that accounts for their different mass numbers.

A student argues that an isotope with a measured mass that is not a whole number must have a fractional number of neutrons. Explain why this reasoning confuses mass number with measured isotope mass.

A sample contains two isotopes: one has a mass of $10.0\,\mathrm{u}$ and an abundance of $75\%$, and the other has a mass of $11.0\,\mathrm{u}$ and an abundance of $25\%$. Calculate the sample’s average atomic mass and show how the abundances enter the calculation.

Two samples contain the same two isotopes, with the same isotope masses, but one sample has a greater fraction of the heavier isotope. Predict which sample has the higher average atomic mass and explain why the individual isotope masses need not change.

Evaluate Dalton’s atomic theory in light of both the evidence that supported it and the later evidence that showed it was incomplete. Identify a lasting useful idea and a claim that had to be revised.

Cathode rays were deflected by electric and magnetic fields, and their properties were consistent across different electrode materials. Explain what these observations support about the rays and atoms, which earlier claim they challenge, and what they do not by themselves establish about the internal arrangement of an atom.

In gold-foil scattering, most alpha particles passed through with little deflection, but a small number were sharply deflected, sometimes back toward the source. Use both observations to infer atomic structure and explain why a model with diffuse positive charge is inadequate.

Explain how the discovery of a neutral nuclear particle with a mass similar to a proton helped resolve the puzzle of different masses among atoms of the same element.

A diagram shows electrons traveling around the nucleus on definite planetary tracks. Contrast that picture with the modern description of electrons and explain how atomic spectra support the modern model.

Two nuclear descriptions give the same atomic number and mass number, but one also specifies a nuclear energy state. Explain what they share and what the additional state information contributes to specifying the nuclide.

A neutral sodium-23 atom has atomic number $Z=11$ and mass number $A=23$. Determine its numbers of protons, neutrons, and electrons, then write its nuclide notation.

Carbon-12 and carbon-13 each have 6 protons. Calculate the neutron count in each and explain why they are isotopes of the same element despite having different mass numbers.

A classmate claims that an isotope’s measured mass must equal its mass number because both describe the atom’s mass. Identify the error and explain how the two quantities differ, including why an isotope’s measured mass is usually not a whole number.

A sample contains two isotopes: one has mass $10.0\,\mathrm{u}$ and abundance $25\%$, and the other has mass $11.0\,\mathrm{u}$ and abundance $75\%$. Calculate the sample’s average atomic mass in $\mathrm{u}$.

Two samples contain the same element and the same isotope types, but in different proportions. Explain why their listed average atomic masses can differ even though the mass of each particular isotope is unchanged. Also explain why neither average is the mass of every atom in its sample.

In the gold-foil experiment, most positively charged alpha particles passed through with little deflection, but a few were sharply deflected or even turned back. Explain how both observations support a model of the atom with mostly open space and a tiny, concentrated, positively charged nucleus.

Explain how Chadwick’s discovery of a neutral nuclear particle helped account for atoms of the same element having different masses without having different element identities.

A diagram shows electrons as tiny planets on fixed circular paths. Describe how the modern quantum-mechanical picture differs and name one kind of measurement that supports it.

Two nuclear labels show the same atomic number but different mass numbers. A student concludes that the labels also tell whether either nucleus is in an excited energy state. Is that conclusion justified? Explain what the labels establish and what additional information is needed when nuclear energy state matters.

Explain how evidence from chemical reactions could support Dalton’s account of compound formation while later evidence still required revising his claim that atoms are indivisible. What does this show about the fate of useful parts of a scientific model?

A researcher finds that one isotope of an element is radioactive. What can be concluded about its relationship to other isotopes of that element regarding proton count, neutron count, mass, chemical identity, and radioactivity? Identify one conclusion about radioactivity that cannot be drawn from that finding alone.

Three nuclides have these values: P has atomic number $Z=8$ and mass number $A=16$; Q has $Z=8$ and $A=18$; R has $Z=9$ and $A=18$. Which pair are isotopes of the same element? Explain using their proton and neutron counts, and explain why the remaining nuclide is not part of that isotope pair.

A hypothetical element has two naturally occurring isotopes: one has a mass of $34.97\ \mathrm{u}$ and an abundance of $75\%$, while the other has a mass of $36.97\ \mathrm{u}$ and an abundance of $25\%$. Calculate the element's average atomic mass and explain how the abundances affect the result.

A neutral atom contains 10 protons, 10 neutrons, and 10 electrons. Treat each proton and neutron as having a mass of approximately $1\,\mathrm{u}$, and each electron as having a mass of approximately $\frac{1}{1836}$ of a proton. Estimate what percentage of the atom's total mass comes from its electrons, and use your estimate to explain where nearly all its mass is concentrated.

In cathode-ray experiments, rays were deflected by electric and magnetic fields, and their properties were consistent even when different electrode materials were used. What conclusions about the rays' charge and their relationship to atoms are supported by these two observations? Explain how those conclusions affected the idea that atoms were indivisible.

In a gold-foil experiment, most positively charged alpha particles passed through with little deflection, but a small number were deflected sharply, some back toward the source. Construct a model of the atom that explains both observations. Your explanation should account for where most of the atom's mass and positive charge are located.

A student says the modern atom is just a tiny solar system, with electrons traveling on fixed paths around the nucleus. Correct this model by explaining what an orbital represents and how atomic spectra relate to support for the modern description.

One unified atomic mass unit is defined as one-twelfth the mass of a carbon-12 atom. A hypothetical atom has a mass 2.5 times the mass of a carbon-12 atom. What is the hypothetical atom's mass in u? Show how you use the definition.