Q: Which formula is used to calculate the average atomic mass of an element with multiple isotopes?

$$\text{Average atomic mass} = \sum (\text{fractional abundance} \times \text{isotope mass})$$

Q: Which of the following is the correct expression for the charge of an atom?

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

Question 1

Which scientist is credited with the discovery of the law of conservation of mass, and what does this law state?

Accepted Answer

Antoine Lavoisier; mass is neither created nor destroyed in a chemical reaction.

Question 2

According to Dalton's atomic theory, which statement is now known to be incorrect?

Accepted Answer

Atoms of a given element are identical in mass and properties.

Question 3

Which experiment provided evidence that most of an atom is empty space and that the nucleus is very small and dense?

Accepted Answer

Rutherford's gold foil experiment

Question 4

What is the charge of an atom with 17 protons and 18 electrons?

Accepted Answer

$$-1$$

Question 5

Which of the following best describes an isotope?

Accepted Answer

Atoms of the same element with different numbers of neutrons.

Question 6

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

Accepted Answer

$$28.09\ \mathrm{u}$$

Question 7

Which of the following elements has only one naturally occurring isotope?

Accepted Answer

Sodium

Question 8

If the atomic number ($$Z) of an $$atom is 15 and its mass number ($$A) is 31$$, how many neutrons does it have?

Accepted Answer

$$16$$

Question 9

Which application uses isotope ratios to determine the year of birth from tooth enamel?

Accepted Answer

Forensic dating using $$^{14}\mathrm{C}$$ levels

Question 10

Which formula is used to calculate the average atomic mass of an element with multiple isotopes?

Accepted Answer

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

Question 11

A gallium sample has two isotopes: $$^{69}\mathrm{Ga} (68.9256 u) $$and $$^{71}\mathrm{Ga} (70.925 u). $$The average atomic mass is 69.723 u. Which isotope is more abundant?

Accepted Answer

$$^{69}\mathrm{Ga}$$

Question 12

Which subatomic particle determines the identity of an element?

Accepted Answer

Proton

Question 13

What is the main difference between isotopes of the same element?

Accepted Answer

Number of neutrons

Question 14

Which of the following is the correct expression for the charge of an atom?

Accepted Answer

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

Question 15

Which technique is commonly used to measure the proportions of isotopes in a sample?

Accepted Answer

Mass spectrometry

Question 16

If an atom has 20 protons, 22 neutrons, and 18 electrons, what is its atomic number, mass number, and charge?

Accepted Answer

Atomic number: 20, Mass number: 42, Charge: $$+2$$

Question 17

Which statement about the nucleus of an atom is correct?

Accepted Answer

It contains most of the atom's mass and is positively charged.

Question 18

Which law states that a chemical compound always contains the same proportion of elements by mass?

Accepted Answer

Law of definite proportions

Question 19

Which of the following is a real-world application of isotopes in geology?

Accepted Answer

Dating rocks using $$^{40}\mathrm{K}$$

Question 20

Which of the following statements about atomic mass is correct?

Accepted Answer

Atomic mass is the weighted average of all naturally occurring isotopes of an element.

Atomic Structure and Nuclear Chemistry I: Foundations of Atomic Theory and Isotopes

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