Question 1

Which of the following statements best explains why the atomic mass of chlorine listed on the periodic table is not a whole number?

Accepted Answer

Because the atomic mass is a weighted average of all naturally occurring isotopes of chlorine.

Question 2

A forensic scientist analyzes a tooth and finds a high ratio of carbon-14 to carbon-12. What can this information most directly help determine?

Accepted Answer

The year of birth of the individual.

Question 3

Which of the following modifications to Dalton’s atomic theory was made after the discovery of isotopes?

Accepted Answer

Atoms of the same element can have different masses due to varying numbers of neutrons.

Question 4

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

Accepted Answer

28.09 u

Question 5

Which of the following best describes the location and relative mass of the subatomic particles in an atom?

Accepted Answer

Protons and neutrons are in the nucleus and account for nearly all the atom's mass; electrons are outside the nucleus and have negligible mass.

Question 6

A neutral atom of gallium has an atomic number of 31 and a mass number of 70. How many neutrons does it contain?

Accepted Answer

39

Question 7

Which of the following real-world applications relies on the law of constant composition?

Accepted Answer

Determining the purity of a pharmaceutical compound by analyzing its elemental ratios.

Question 8

A mass spectrometry analysis of a sample shows two peaks for gallium: one at 68.9256 u and another at 70.925 u. The average atomic mass of gallium is 69.723 u. Which isotope is more abundant?

Accepted Answer

68.9256 u isotope

Question 9

Which of the following best describes an isotope?

Accepted Answer

Atoms of the same element with different numbers of neutrons.

Question 10

A certain atom has 17 protons, 18 neutrons, and 18 electrons. What is the charge and identity of this atom?

Accepted Answer

Chloride ion with a -1 charge

Question 11

Which experiment or observation most directly led to the conclusion that most of the atom is empty space?

Accepted Answer

Rutherford’s gold foil experiment, where most alpha particles passed through the foil.

Question 12

Which of the following is a correct representation of a carbon isotope with 6 protons and 8 neutrons?

Accepted Answer

14C or 14/6 C or $$14^6C $$are all correct notations.

Question 13

Which statement about nucleons is correct?

Accepted Answer

Nucleons are protons and neutrons found in the nucleus.

Question 14

A sample contains 80% isotope X (mass = 10 u) and 20% isotope Y (mass = 11 u). What is the average atomic mass of the element?

Accepted Answer

10.2 u

Question 15

Which of the following best explains why changing the number of protons in an atom changes the element?

Accepted Answer

The number of protons defines the atomic number, which uniquely identifies the element.

Question 16

Which of the following is a real-world application of mass spectrometry?

Accepted Answer

Determining the isotopic composition of lead in ancient Roman pipes to trace their origin.

Question 17

Which of the following best describes the law of conservation of mass?

Accepted Answer

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

Question 18

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

Accepted Answer

Electrons are found outside the nucleus and have a negative charge.

Question 19

Which of the following best explains why isotopic analysis is useful in archaeology?

Accepted Answer

It helps determine the age of samples by measuring the ratios of radioactive isotopes.

Question 20

Which of the following is the correct formula for calculating the charge of an atom?

Accepted Answer

Charge = number of protons - number of electrons

Atomic Structure and Nuclear Chemistry: Foundations and Applications

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