Q: Which of the following equations correctly represents the relationship between the charge of an atom, the number of protons, and the number of electrons?

$\text{Charge} = \#\text{protons} - \#\text{electrons}$

Question 1

Which of the following statements best describes the law of conservation of mass as discovered by Antoine Lavoisier?

Accepted Answer

The total mass of substances before and after a chemical reaction remains unchanged.

Question 2

A sample of silicon contains three naturally occurring isotopes: $^{28}\mathrm{Si}$ (92.23%, 27.9769 u), $^{29}\mathrm{Si}$ (4.67%, 28.9765 u), and $^{30}\mathrm{Si}$ (3.10%, 29.9738 u). What is the average atomic mass of silicon? (Round to two decimal places.)

Accepted Answer

$28.09\ \mathrm{u}$

Question 3

Which experiment provided evidence that most of the mass of an atom is concentrated in a tiny, positively charged nucleus?

Accepted Answer

Rutherford's gold foil experiment

Question 4

Which of the following is true about isotopes of an element?

Accepted Answer

They have the same number of protons but different numbers of neutrons.

Question 5

A neutral atom of chlorine has an atomic number of 17 and a mass number of 35. How many protons, neutrons, and electrons does it have?

Accepted Answer

17 protons, 18 neutrons, 17 electrons

Question 6

Which of the following best explains why atomic masses on the periodic table are not whole numbers?

Accepted Answer

They are weighted averages of all naturally occurring isotopes of each element.

Question 7

Which of the following statements about Dalton’s atomic theory is no longer considered completely accurate?

Accepted Answer

All atoms of a given element are identical in mass and in all other properties.

Question 8

A forensic scientist uses the ratio of $^{14}\mathrm{C}$ to $^{12}\mathrm{C}$ in tooth enamel to estimate a person's year of birth. This method relies on which property of isotopes?

Accepted Answer

The changing atmospheric levels of $^{14}\mathrm{C}$ over time are recorded in biological tissues.

Question 9

Which of the following equations correctly represents the relationship between the charge of an atom, the number of protons, and the number of electrons?

Accepted Answer

$	ext{Charge} = \#	ext{protons} - \#	ext{electrons}$

Question 10

Gallium has two naturally occurring isotopes: $^{69}\mathrm{Ga}$ (68.93 u) and $^{71}\mathrm{Ga}$ (70.925 u). The average atomic mass of gallium is 69.723 u. Which isotope is more abundant, and why?

Accepted Answer

$^{69}\mathrm{Ga}$ is more abundant because the average atomic mass is closer to its mass.

Question 11

Which of the following best describes a nucleon?

Accepted Answer

A nucleon is a general term for a proton or neutron.

Question 12

A sample contains 75% isotope X (mass = 10 u) and 25% isotope Y (mass = 12 u). What is the average atomic mass of the element?

Accepted Answer

$10.5\ \mathrm{u}$

Question 13

Which of the following is a direct consequence of the law of definite proportions?

Accepted Answer

A chemical compound always contains the same elements in the same ratio by mass.

Question 14

Which of the following statements about the structure of the atom is correct?

Accepted Answer

Most of the atom's mass is concentrated in the nucleus, which is very small compared to the overall size of the atom.

Question 15

Which of the following best describes the main difference between isotopes of the same element?

Accepted Answer

They have different numbers of neutrons.

Question 16

Which of the following real-world applications relies on the measurement of isotope ratios?

Accepted Answer

Dating archaeological samples using $^{14}\mathrm{C}$ analysis.

Question 17

If an atom has 15 protons, 16 neutrons, and 18 electrons, what is its charge?

Accepted Answer

$-3$

Question 18

Which of the following best describes mass spectrometry?

Accepted Answer

A technique that separates isotopes based on their mass-to-charge ratio.

Question 19

Which of the following is NOT a postulate of Dalton’s original atomic theory?

Accepted Answer

Atoms can be subdivided into protons, neutrons, and electrons.

Atomic Structure and Nuclear Chemistry: Foundations and Applications

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