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 present after a chemical reaction is the same as the total mass before the reaction.

Question 2

Which of the following is NOT a postulate of John Dalton's atomic theory as originally proposed in 1808?

Accepted Answer

Atoms of a given element can have different masses due to isotopes.

Question 3

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 contain?

Accepted Answer

17 protons, 18 neutrons, 17 electrons

Question 4

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 5

The atomic number ($$Z) of an $$element is defined as:

Accepted Answer

The number of protons in the nucleus

Question 6

Which of the following best explains why isotopes of the same element have different mass numbers?

Accepted Answer

They have different numbers of neutrons.

Question 7

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

Accepted Answer

$$28.09\ \mathrm{u}$$

Question 8

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

Accepted Answer

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

Question 9

If an atom has 15 protons, 16 neutrons, and 15 electrons, what is its mass number and what element is it?

Accepted Answer

Mass number = 31, element = phosphorus

Question 10

Which of the following statements about mass spectrometry is correct?

Accepted Answer

It separates isotopes based on their mass-to-charge ratio.

Question 11

Gallium has two naturally occurring isotopes: $$^{69}Ga (68.9256 u) $$and $$^{71}Ga (70.925 u). $$The average atomic mass of gallium is 69.723 u. Which isotope is more abundant?

Accepted Answer

$$^{69}Ga$$

Question 12

Which of the following best describes a nucleon?

Accepted Answer

A particle in the nucleus, i.e., a proton or neutron

Question 13

Which of the following would change the identity of an element?

Accepted Answer

Changing the number of protons in the nucleus

Question 14

A neutral atom has 20 protons and 22 neutrons. What is its atomic number and mass number?

Accepted Answer

Atomic number = 20, mass number = 42

Question 15

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

Accepted Answer

$$	ext{Average atomic mass} = \sum (	ext{fractional abundance} 	imes 	ext{isotopic mass})$$

Question 16

Which of the following statements about atoms is correct?

Accepted Answer

Most of the volume of an atom is empty space.

Question 17

If a neutral atom becomes an ion with a charge of $$+2$$, what has happened to its electrons?

Accepted Answer

It has lost two electrons.

Question 18

Which of the following is a correct statement about isotopes?

Accepted Answer

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

Question 19

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

Accepted Answer

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

Question 20

Which of the following would be the result of changing the number of neutrons in an atom?

Accepted Answer

A different isotope of the same element

Atomic Structure and Nuclear Chemistry: Foundations and Applications

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