$$\text{Atomic mass} = (\text{fractional abundance}_1 \times \text{mass}_1) + (\text{fractional abundance}_2 \times \text{mass}_2)$$

$$(0.7577 \times 34.97) + (0.2423 \times 36.97) = 35.45$$ amu

Question 1

Which experiment provided the evidence that led to the rejection of the plum-pudding model of the atom?

Accepted Answer

Rutherford’s gold foil experiment

Question 2

Which of the following statements best describes the modern nuclear model of the atom?

Accepted Answer

Most of the atom’s mass and all its positive charge are concentrated in a small nucleus, with electrons occupying most of the volume.

Question 3

A neutral atom of magnesium (Mg) has an atomic number of 12 and a mass number of 24. How many protons, neutrons, and electrons does it contain?

Accepted Answer

12 protons, 12 neutrons, 12 electrons

Question 4

Which property is NOT characteristic of metals?

Accepted Answer

Tends to gain electrons in chemical reactions

Question 5

Which element is defined by having 17 protons in its nucleus?

Accepted Answer

Chlorine

Question 6

A fluorine atom gains one electron to form an ion. What is the charge and name of this ion?

Accepted Answer

$$	ext{F}^-$$, fluoride anion

Question 7

Which of the following best explains why noble gases are chemically inert?

Accepted Answer

They have a full set of valence electrons, making them stable.

Question 8

Which group in the periodic table contains elements that are highly reactive nonmetals?

Accepted Answer

Halogens

Question 9

How many neutrons are in an isotope of carbon-14?

Accepted Answer

8

Question 10

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

Accepted Answer

$$	ext{Atomic mass} = (	ext{fractional abundance}_1 	imes 	ext{mass}_1) + (	ext{fractional abundance}_2 	imes 	ext{mass}_2)$$

Question 11

A sample of chlorine contains 75.77% chlorine-35 (mass 34.97 amu) and 24.23% chlorine-37 (mass 36.97 amu). What is the atomic mass of chlorine?

Accepted Answer

$$(0.7577 	imes 34.97) + (0.2423 	imes 36.97) = 35.45$$ amu

Question 12

Which of the following statements about isotopes is TRUE?

Accepted Answer

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

Question 13

Which of the following elements is a metalloid and is widely used in the electronics industry?

Accepted Answer

Silicon

Question 14

Which of the following best describes the difference between cations and anions?

Accepted Answer

Cations are positively charged ions formed by losing electrons; anions are negatively charged ions formed by gaining electrons.

Question 15

Which scientist is credited with organizing the periodic table based on recurring properties and increasing atomic mass?

Accepted Answer

Dmitri Mendeleev

Question 16

A sodium atom (Na) loses one electron during a chemical reaction. What is the resulting ion and its charge?

Accepted Answer

$$	ext{Na}^+$$, sodium cation

Question 17

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

Accepted Answer

Technetium-99 is used in medical imaging to diagnose diseases.

Question 18

Which of the following best explains why matter is usually electrically neutral?

Accepted Answer

Matter contains equal numbers of protons and electrons, so their charges cancel.

Question 19

Which of the following is a property of nonmetals?

Accepted Answer

Poor conductor of heat and electricity

Question 20

Which of the following best describes the periodic law as observed by Mendeleev?

Accepted Answer

When elements are arranged in order of increasing atomic mass, certain sets of properties recur periodically.

Atoms and Elements: Foundations of Chemistry

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