Subtract the atomic number from the mass number: $$\text{Number of neutrons} = \text{Mass number} - \text{Atomic number}$$

Question 1

Which of the following best describes the difference between an element and a compound?

Accepted Answer

An element is a substance that cannot be broken down by chemical reactions, while a compound consists of two or more elements in a fixed ratio.

Question 2

Which four elements make up approximately 96% of living matter?

Accepted Answer

Carbon, hydrogen, oxygen, and nitrogen

Question 3

Which of the following is a trace element required by humans and what is its function?

Accepted Answer

Iodine; necessary for proper thyroid function

Question 4

Which naturally occurring element is toxic to most living organisms?

Accepted Answer

Arsenic

Question 5

How can you determine the number of neutrons in an atom?

Accepted Answer

Subtract the atomic number from the mass number: $$	ext{Number of neutrons} = 	ext{Mass number} - 	ext{Atomic number}$$

Question 6

Which statement best explains why electrons in the first electron shell have less potential energy than those in higher shells?

Accepted Answer

They are closer to the nucleus, so their energy is lower due to the attractive force of the protons.

Question 7

Which of the following best describes the difference between a nonpolar covalent bond and a polar covalent bond?

Accepted Answer

Nonpolar covalent bonds share electrons equally, while polar covalent bonds share electrons unequally.

Question 8

Which of the following is an example of a biological application that uses radioactive isotopes?

Accepted Answer

Using $$^{14}C to $$date ancient fossils

Question 9

What is the main reason weak bonds, such as hydrogen bonds and van der Waals interactions, are important in living organisms?

Accepted Answer

They allow large biological molecules to maintain their functional shapes and to be easily broken and reformed.

Question 10

Which of the following best describes chemical equilibrium?

Accepted Answer

The forward and reverse reactions occur at the same rate, so the concentrations of reactants and products remain constant.

Question 11

A sodium atom ($$Na) $$reacts with a chlorine atom ($$Cl) to $$form sodium chloride ($$NaCl). $$Which of the following best describes this process?

Accepted Answer

A sodium atom transfers an electron to a chlorine atom, forming $$Na^+$$ and $$Cl^-$$ ions that are held together by ionic bonds.

Question 12

Which of the following molecules is held together primarily by hydrogen bonds in biological systems?

Accepted Answer

Water molecules ($$H_2O)$$

Question 13

Which of the following best explains why the shape of a molecule is important in biology?

Accepted Answer

The shape determines how molecules recognize and respond to each other, affecting biological function.

Question 14

Which of the following is the correct Lewis dot structure for a hydrogen molecule ($$H_2$$)?

Accepted Answer

$$H : H$$

Question 15

A patient is exposed to a radioactive isotope for cancer treatment. Which property of radioactive isotopes makes them useful for this application?

Accepted Answer

They emit radiation that can damage or destroy cancer cells.

Question 16

Which of the following best describes the difference between atomic number and mass number?

Accepted Answer

Atomic number is the number of protons; mass number is the sum of protons and neutrons.

Question 17

Which of the following is a real-world example of a chemical reaction important for life, and what is its balanced equation?

Accepted Answer

Photosynthesis: $$6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6$ + 6O_2$$

Question 18

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 19

Which of the following best explains why covalent bonds are important in biological molecules?

Accepted Answer

They provide the stability needed for the structure of large molecules like DNA and proteins.

The Chemical Context of Life: Elements, Atoms, and Chemical Bonds

Study Guide - Practice Questions