Question 1

Which of the following statements about Dalton's atomic theory is no longer considered entirely accurate based on modern scientific understanding?

Accepted Answer

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

Question 2

A forensic scientist is analyzing tooth enamel to estimate a person's year of birth. Which isotope is most relevant for this analysis, and why?

Accepted Answer

14C, because its abundance in enamel reflects atmospheric levels at the time the enamel formed.

Question 3

Which experiment or law provided the strongest evidence that mass is conserved during chemical reactions?

Accepted Answer

Law of conservation of mass (Lavoisier)

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?

Accepted Answer

16

Question 5

Which of the following best explains why isotopes of the same element have nearly identical chemical properties?

Accepted Answer

They have the same number of protons and electrons.

Question 6

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 to four decimal places?

Accepted Answer

28.0855 u

Question 7

Which of the following statements about mass spectrometry is correct?

Accepted Answer

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

Question 8

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

Accepted Answer

69Ga, because the average atomic mass is closer to its mass.

Question 9

Which of the following changes would result in the formation of a different element?

Accepted Answer

Changing the number of protons in the nucleus.

Question 10

A neutral atom of an element has 20 protons, 20 neutrons, and 20 electrons. What is the atomic number and mass number of this atom?

Accepted Answer

Atomic number = 20, mass number = 40

Question 11

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

Accepted Answer

Electrons are found outside the nucleus and have negligible mass compared to protons and neutrons.

Question 12

Which of the following is a correct application of the law of constant composition?

Accepted Answer

Water from any source always contains hydrogen and oxygen in the same proportion by mass.

Question 13

A sample of an element contains atoms with 35 protons and 45 neutrons. What is the correct isotope notation for this atom?

Accepted Answer

80Br

Question 14

Which of the following best explains why the atomic mass of an element on the periodic table is rarely a whole number?

Accepted Answer

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

Question 15

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 16

A sample of gallium contains 60% 69Ga (68.9256 u) and 40% 71Ga (70.925 u). What is the calculated average atomic mass of this sample?

Accepted Answer

69.525 u

Question 17

Which of the following best describes the main difference between isotopes of the same element as detected by mass spectrometry?

Accepted Answer

Their mass-to-charge ratio

Question 18

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

Accepted Answer

Determining the age of archaeological artifacts using radiocarbon dating

Question 19

If an atom has a charge of +2, 20 protons, and 18 electrons, what is its atomic number?

Accepted Answer

20

Question 20

Which of the following best explains why most of the mass of an atom is concentrated in its nucleus?

Accepted Answer

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

Atomic Structure and Nuclear Chemistry: Foundations and Applications

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