Q: Millikan’s oil drop experiment allowed for the calculation of the charge of a single electron. Which equation did Millikan use to equate the forces acting on the oil droplet?

$$\text{Force}_{\text{gravity}} = \text{Force}_{\text{electrostatic}}$$

Question 1

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

Accepted Answer

Atoms of one element cannot change into atoms of another element.

Question 2

Marie Curie coined the term 'radioactivity.' What evidence did radioactivity provide about the nature of atoms?

Accepted Answer

Atoms are made of smaller particles.

Question 3

In Thompson’s cathode ray experiment, what property of the cathode ray led to the conclusion that it was composed of electrons?

Accepted Answer

The ray was deflected by electric and magnetic fields.

Question 4

Which of the following best describes the charge-to-mass ratio ($$\frac{e}{m}) $$determined by Thompson for the electron?

Accepted Answer

$$\frac{e}{m} is a $$constant for all electrons, regardless of the cathode material.

Question 5

Millikan’s oil drop experiment allowed for the calculation of the charge of a single electron. Which equation did Millikan use to equate the forces acting on the oil droplet?

Accepted Answer

$$	ext{Force}_{	ext{gravity}} = 	ext{Force}_{	ext{electrostatic}}$$

Question 6

Which model of the atom was disproven by Rutherford’s gold foil experiment?

Accepted Answer

Plum pudding model

Question 7

Rutherford’s gold foil experiment led to which major conclusion about atomic structure?

Accepted Answer

Most of the atom’s mass and all its positive charge are concentrated in a small nucleus.

Question 8

Which subatomic particle was discovered by James Chadwick, completing the modern atomic model?

Accepted Answer

Neutron

Question 9

An atom of Nitrogen-15 has how many neutrons?

Accepted Answer

8

Question 10

Which formula correctly relates the mass number ($$A$$), atomic number ($$Z$$), and number of neutrons ($$N) in an $$atom?

Accepted Answer

$$A = Z + N$$

Question 11

Which of the following statements about isotopes is correct?

Accepted Answer

Isotopes of an element have the same atomic number but different mass numbers.

Question 12

Given the natural abundances and atomic masses of Boron isotopes: $$^{10}B (20.0$$%, 10.0129 amu) and $$^{11}B (80.0$$%, 11.0093 amu), what is the atomic weight of Boron?

Accepted Answer

$$10.8$$ amu

Question 13

Copper has two stable isotopes, Cu-63 and Cu-65, with atomic masses of $$62.929599 u $$and $$64.927793 u$$, respectively. If the atomic weight of copper is $$63.546 u$$, what is the percent abundance of Cu-63?

Accepted Answer

$$69.152\%$$

Question 14

Which statement is NOT true regarding Fe-56?

Accepted Answer

Mass number of Fe-56 is 55.845

Question 15

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

Accepted Answer

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

Question 16

Which hydrogen isotope is radioactive?

Accepted Answer

Tritium

Question 17

If an atom has 12 protons, 12 neutrons, and 12 electrons, what is its atomic number and mass number?

Accepted Answer

Atomic number $$= 12$$, mass number $$= 24$$

Question 18

Which of the following is the correct definition of atomic mass unit (amu)?

Accepted Answer

One amu is defined as exactly $$\frac{1}{12}$$ the mass of a $$^{12}C$$ atom.

Question 19

Which statement best explains why atomic weights are not whole numbers?

Accepted Answer

Atomic weights are weighted averages of the masses of all naturally occurring isotopes.

Foundations of Atomic Theory: Dalton, Radioactivity, and the Electron

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