Question 1

Which of the following best explains why the atomic mass of chlorine listed on the periodic table is not a whole number?
Correct answer: It is a weighted average of the masses of all naturally occurring isotopes of chlorine.

Accepted Answer

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

Question 2

A sample of magnesium contains 78.99% 24Mg (23.985 amu), 10.00% 25Mg (24.986 amu), and 11.01% 26Mg (25.983 amu). What is the average atomic mass of magnesium? (Round to two decimal places.)
Correct answer: 24.31 amu

Accepted Answer

24.31 amu

Question 3

Which statement about isotopes is correct?
Correct answer: Isotopes of an element have the same number of protons but different numbers of neutrons.

Accepted Answer

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

Question 4

A neutral atom of phosphorus has an atomic number of 15 and a mass number of 31. How many neutrons does it contain?
Correct answer: 16

Accepted Answer

16

Question 5

Which experiment or law provided the first strong evidence that matter is conserved in chemical reactions?
Correct answer: Lavoisier's law of conservation of mass

Accepted Answer

Lavoisier's law of conservation of mass

Question 6

A forensic scientist analyzes a tooth and finds a 14C/12C ratio consistent with atmospheric levels from the 1960s. What can be inferred from this data?
Correct answer: The individual was likely born in the 1960s.

Accepted Answer

The individual was likely born in the 1960s.

Question 7

Which of the following best describes the structure of an atom according to modern understanding?
Correct answer: A dense nucleus containing protons and neutrons, surrounded by electrons in mostly empty space.

Accepted Answer

A dense nucleus containing protons and neutrons, surrounded by electrons in mostly empty space.

Question 8

Which of the following is NOT a postulate of Dalton’s atomic theory?
Correct answer: Atoms of the same element can have different numbers of neutrons.

Accepted Answer

Atoms of the same element can have different numbers of neutrons.

Question 9

A sample contains two isotopes of element X: 60% X-29 (mass = 29 amu) and 40% X-30 (mass = 30 amu). What is the average atomic mass of element X?
Correct answer: 29.4 amu

Accepted Answer

29.4 amu

Question 10

Which of the following real-world applications relies on the measurement of isotope ratios?
Correct answer: Determining the age of archaeological artifacts using radiocarbon dating

Accepted Answer

Determining the age of archaeological artifacts using radiocarbon dating

Question 11

If an atom has 17 protons, 18 neutrons, and 17 electrons, what is its mass number and net charge?
Correct answer: Mass number = 35, net charge = 0

Accepted Answer

Mass number = 35, net charge = 0

Question 12

Which statement best explains the law of definite proportions?
Correct answer: A chemical compound always contains the same elements in the same ratio by mass.

Accepted Answer

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

Question 13

Which of the following would NOT be detected as a different peak in a mass spectrometer?
Correct answer: Two atoms of the same element with the same number of protons and neutrons

Accepted Answer

Two atoms of the same element with the same number of protons and neutrons

Question 14

Which of the following best describes the main difference between protons and neutrons?
Correct answer: Protons have a positive charge, while neutrons are neutral.

Accepted Answer

Protons have a positive charge, while neutrons are neutral.

Question 15

A neutral atom of element Q has 20 electrons and 22 neutrons. What is the identity of element Q?
Correct answer: Calcium (atomic number 20)

Accepted Answer

Calcium (atomic number 20)

Question 16

Which of the following scenarios would violate Dalton’s atomic theory as originally stated?
Correct answer: Atoms of the same element having different masses

Accepted Answer

Atoms of the same element having different masses

Question 17

Which of the following best explains why most of the mass of an atom is concentrated in its nucleus?
Correct answer: Protons and neutrons, which are much more massive than electrons, are located in the nucleus.

Accepted Answer

Protons and neutrons, which are much more massive than electrons, are located in the nucleus.

Question 18

Which of the following is a correct application of the law of conservation of mass?
Correct answer: The total mass of reactants in a chemical reaction equals the total mass of products.

Accepted Answer

The total mass of reactants in a chemical reaction equals the total mass of products.

Question 19

A scientist uses mass spectrometry to analyze a sample and finds two peaks corresponding to masses of 63 and 65 amu. What does this indicate about the sample?
Correct answer: The sample contains two isotopes of the same element.

Accepted Answer

The sample contains two isotopes of the same element.

Atomic Structure and Nuclear Chemistry: Key Concepts

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