Question 1

Which statement from Dalton’s atomic theory has been disproven by later scientific discoveries?

Accepted Answer

All atoms of a given element have the same mass and other properties that distinguish them from the atoms of other elements.

Question 2

Which real-world phenomenon provided evidence that atoms are made of smaller particles, contradicting Dalton’s idea of indivisible atoms?

Accepted Answer

Radioactivity

Question 3

In J.J. Thompson’s cathode ray experiment, which observation led to the conclusion that cathode rays are composed of negatively charged particles?

Accepted Answer

The rays could be deflected by electric and magnetic fields.

Question 4

Which of the following best describes the significance of Marie Curie’s work in the context of atomic theory?

Accepted Answer

She coined the term 'radioactivity' and provided evidence that atoms are not indivisible.

Question 5

Which of the following is NOT a property of the particles that compose the cathode ray, as discovered by Thompson?

Accepted Answer

They have a positive electrical charge.

Question 6

Which experiment first demonstrated that atoms contain a small, dense, positively charged nucleus?

Accepted Answer

Rutherford’s gold foil experiment

Question 7

According to Rutherford’s gold foil experiment, what was the most surprising observation?

Accepted Answer

Most alpha particles passed straight through the foil, but some were deflected at large angles.

Question 8

Which of the following statements about isotopes is correct?

Accepted Answer

Isotopes of an element have the same number of protons but different numbers of neutrons.

Question 9

A sample of boron contains 20.0% $$^{10}B (10.0129 $$amu) and 80.0% $$^{11}B (11.0093 $$amu). What is the atomic weight of boron? Use the weighted average formula: $$	ext{Atomic weight} = (	ext{fraction}_1 	imes 	ext{mass}_1) + (	ext{fraction}_2 	imes 	ext{mass}_2).$$

Accepted Answer

$$10.8$$ amu

Question 10

Which of the following statements about the atomic nucleus is correct according to Rutherford’s model?

Accepted Answer

The nucleus contains most of the atom’s mass and all of its positive charge.

Question 11

Which of the following is the correct definition of atomic number ($$Z$$)?

Accepted Answer

The number of protons in the nucleus of an atom.

Question 12

A neutral atom of nitrogen-15 ($$^{15}N) $$has how many neutrons?

Accepted Answer

8

Question 13

Which of the following best explains why the atomic mass of an element is not a whole number?

Accepted Answer

It is a weighted average of the masses of all naturally occurring isotopes.

Question 14

Which of the following is NOT true regarding Fe-56?

Accepted Answer

Mass number is 55.845.

Question 15

Copper has two stable isotopes: Cu-63 (62.929599 u) and Cu-65 (64.927793 u). If the atomic mass of copper is 63.546 u, what is the fractional abundance of Cu-63? Use the equation: $$x(62.929599) + (1-x)(64.927793) = 63.546.$$

Accepted Answer

0.6915

Question 16

Which of the following statements about protons, neutrons, and electrons is correct?

Accepted Answer

Protons and electrons have equal but opposite charges.

Question 17

Which isotope notation correctly represents an atom with 5 protons and 6 neutrons?

Accepted Answer

$$^{11}_{5}B$$

Question 18

Which of the following best describes the difference between the plum pudding model and the nuclear model of the atom?

Accepted Answer

The plum pudding model has electrons embedded in a positively charged sphere, while the nuclear model has a dense nucleus with electrons outside.

Question 19

Which experiment allowed for the calculation of the charge of a single electron?

Accepted Answer

Millikan’s oil drop experiment

Question 20

Which force was balanced against gravity in Millikan’s oil drop experiment to determine the charge on an electron?

Accepted Answer

Electrostatic force

Foundations of Atomic Theory: Early Discoveries in Chemistry

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