$$\text{Mass number} = \text{Number of protons} + \text{Number of neutrons}$$

Question 1

Which of the following best explains why table salt (NaCl) is considered to have emergent properties?

Accepted Answer

Because sodium is a reactive metal and chlorine is a poisonous gas, but together they form an edible compound with new properties.

Question 2

Which four elements make up approximately 96% of the mass of most living organisms?

Accepted Answer

Oxygen, carbon, hydrogen, nitrogen

Question 3

A compound is best defined as:

Accepted Answer

A substance consisting of two or more elements in a fixed ratio

Question 4

Which of the following statements about trace elements is correct?

Accepted Answer

Trace elements are required in minute quantities but are essential for health, such as iodine to prevent goiter.

Question 5

An atom of nitrogen has 7 protons and 9 neutrons. What is its atomic number and mass number?

Accepted Answer

Atomic number = 7, Mass number = 16

Question 6

Which subatomic particles are found in the nucleus of an atom?

Accepted Answer

Protons and neutrons

Question 7

Isotopes of an element differ in which of the following?

Accepted Answer

Number of neutrons

Question 8

Which of the following best describes an ionic bond?

Accepted Answer

A bond formed by the transfer of electrons from one atom to another, resulting in oppositely charged ions that attract each other

Question 9

What holds together the ions in a crystal of table salt (NaCl)?

Accepted Answer

The attraction between oppositely charged ions

Question 10

Which of the following best explains why water molecules are polar?

Accepted Answer

Because oxygen is more electronegative than hydrogen, resulting in unequal sharing of electrons

Question 11

How many covalent bonds can a carbon atom typically form, and why?

Accepted Answer

Four, because it has four electrons in its outer shell and needs four more to fill it

Question 12

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

Accepted Answer

$$	ext{Mass number} = 	ext{Number of protons} + 	ext{Number of neutrons}$$

Question 13

A patient is diagnosed with goiter, a swelling of the thyroid gland. Which trace element deficiency is most likely responsible?

Accepted Answer

Iodine

Question 14

Which of the following best describes a covalent bond?

Accepted Answer

A bond in which two atoms share one or more pairs of electrons

Question 15

Which of the following is a real-world example of a compound with polar covalent bonds?

Accepted Answer

Water ($$H_2O)$$

Question 16

If an atom has an atomic number of 12 and a mass number of 25, how many neutrons does it have?

Accepted Answer

$$25 - 12 = 13$$ neutrons

Question 17

Which of the following best describes the difference between a molecule of $$O_2$$ and a molecule of $$H_2O$$?

Accepted Answer

$$O_2 is a $$nonpolar molecule with a double covalent bond, while $$H_2O is a $$polar molecule with single covalent bonds.

Question 18

Which of the following statements about electron shells is correct?

Accepted Answer

Atoms with incomplete outer electron shells tend to react with other atoms to achieve stability.

Question 19

Which of the following best explains why sodium (Na) and chlorine (Cl) form an ionic bond in table salt?

Accepted Answer

Sodium donates an electron to chlorine, resulting in oppositely charged ions that attract each other.

Question 20

Which of the following is a correct statement about the relationship between atoms, elements, and compounds?

Accepted Answer

Elements are made of one kind of atom, and compounds are made of two or more elements in a fixed ratio.

Chapter 2: The Chemical Basis of Life – Elements, Atoms, and Compounds

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