Q: Which of the following is the correct formula for calculating the average atomic mass of an element with two isotopes?

$$M_{av} = \frac{\text{abundance}_1}{100} \times M_1$ + \frac{\text{abundance}_2}{100} \times M_2$

Q: Which of the following best describes the charge of an atom?

Charge $$= \text{number of protons} - \text{number of electrons}$$

Question 1

Which experiment provided the first direct evidence that atoms have a small, dense, positively charged nucleus?

Accepted Answer

Rutherford’s gold foil experiment

Question 2

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 3

A neutral atom of gold has 79 protons and 118 neutrons. What is its mass number?

Accepted Answer

$$197$$

Question 4

Which law states that a chemical compound always contains the same proportion of elements by mass?

Accepted Answer

Law of constant composition (law of definite proportions)

Question 5

Which subatomic particle is responsible for the chemical identity of an element?

Accepted Answer

Proton

Question 6

A sample contains $$92.23\%$$ $$^{28}\mathrm{Si} ($$mass $$= 27.9769 u$$), $$4.67\%$$ $$^{29}\mathrm{Si} ($$mass $$= 28.9765 u$$), and $$3.10\%$$ $$^{30}\mathrm{Si} ($$mass $$= 29.9738 u). $$What is the average atomic mass of silicon?

Accepted Answer

$$28.09 u$$

Question 7

Which of the following best describes the result of mass spectrometry?

Accepted Answer

A spectrum showing the proportion of atoms in the sample belonging to each isotope

Question 8

Which of the following is a real-world application of isotope ratios?

Accepted Answer

Determining the year of birth from tooth enamel using $$^{14}\mathrm{C}$$

Question 9

Which of the following statements about Dalton’s atomic theory is NOT correct according to modern understanding?

Accepted Answer

Atoms are indestructible and retain their identity in all chemical reactions.

Question 10

A neutral atom has 17 protons, 18 neutrons, and 17 electrons. What is its atomic number and mass number?

Accepted Answer

Atomic number $$= 17$$, mass number $$= 35$$

Question 11

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

Accepted Answer

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

Question 12

Which of the following is the correct formula for calculating the average atomic mass of an element with two isotopes?

Accepted Answer

$$M_{av} = \frac{	ext{abundance}_1}{100} 	imes M_1$ + \frac{	ext{abundance}_2}{100} 	imes M_2$

Question 13

Gallium has two naturally occurring isotopes: $$^{69}\mathrm{Ga} ($$mass $$= 68.926 u) $$and $$^{71}\mathrm{Ga} ($$mass $$= 70.925 u). $$The average atomic mass is $$69.723 u. $$Which isotope is more abundant?

Accepted Answer

$$^{69}\mathrm{Ga}$$

Question 14

Which of the following best describes the charge of an atom?

Accepted Answer

Charge $$= 	ext{number of protons} - 	ext{number of electrons}$$

Question 15

Which of the following is a correct statement about the nucleus of an atom?

Accepted Answer

It contains most of the atom’s mass but occupies a tiny fraction of its volume.

Question 16

Which of the following is a practical application of nuclear chemistry in medicine?

Accepted Answer

Using technetium isotopes for imaging internal organs

Question 17

Which of the following best explains why most alpha particles passed straight through the gold foil in Rutherford’s experiment?

Accepted Answer

Most of the atom is empty space.

Question 18

Which of the following is a correct description of a nucleon?

Accepted Answer

A particle in the nucleus, either a proton or a neutron

Question 19

Which of the following is the best explanation for why changing the number of protons in an atom changes the element?

Accepted Answer

The atomic number, which defines the element, is equal to the number of protons.

Atomic Structure and Nuclear Chemistry: Foundations and Applications

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