Question 1

Which of the following statements best explains why sodium chloride (NaCl) has properties different from both pure sodium and pure chlorine?

Accepted Answer

The chemical reaction between sodium and chlorine forms a compound with a fixed ratio and new properties.

Question 2

Which four elements make up approximately 96% of living matter in the human body?

Accepted Answer

Oxygen, carbon, hydrogen, and nitrogen

Question 3

An atom of carbon-14 ($$^{14}C) $$has 6 protons and 8 neutrons. What is its atomic number and mass number?

Accepted Answer

Atomic number: 6, Mass number: 14

Question 4

Which of the following best describes a trace element?

Accepted Answer

An element required by an organism in minute quantities

Question 5

If an atom has 11 protons, 12 neutrons, and 11 electrons, what is its atomic number and is it electrically neutral?

Accepted Answer

Atomic number: 11; Yes, it is neutral

Question 6

Which type of chemical bond involves the sharing of a pair of valence electrons between two atoms?

Accepted Answer

Covalent bond

Question 7

A radioactive isotope decays with a half-life of 5,000 years. If a fossil contains 25% of its original radioactive isotope, how many half-lives have passed?

Accepted Answer

Two half-lives

Question 8

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

Accepted Answer

Polar covalent bonds share electrons unequally due to differences in electronegativity; nonpolar covalent bonds share electrons equally.

Question 9

Which statement about chemical reactions is correct?

Accepted Answer

Chemical reactions must be balanced, meaning all atoms in reactants are accounted for in products.

Question 10

What is the main reason that atoms with incomplete valence shells are chemically reactive?

Accepted Answer

They seek to complete their valence shell by gaining, losing, or sharing electrons.

Question 11

Which of the following is an example of a weak chemical bond that is crucial for reinforcing the shapes of large biological molecules?

Accepted Answer

Hydrogen bond

Question 12

A molecule of methane ($$CH_4) $$has a tetrahedral shape. What determines this three-dimensional shape?

Accepted Answer

The arrangement of electron orbitals involved in covalent bonding

Question 13

Which of the following best describes van der Waals interactions?

Accepted Answer

Weak attractions due to transient partial charges in molecules or atoms in close proximity

Question 14

If a molecule has regions of partial positive and partial negative charge, which type of bond is most likely present?

Accepted Answer

Polar covalent bond

Question 15

Which of the following is true about isotopes of an element?

Accepted Answer

They have the same number of protons but different numbers of neutrons.

Question 16

Which equation correctly represents the balanced chemical reaction for the formation of water from hydrogen and oxygen?

Accepted Answer

$$2H_2 + O_2$ \rightarrow 2H_2O$$

Question 17

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

Accepted Answer

Molecules with similar shapes can have similar biological effects by binding to the same receptors.

Question 18

Which of the following statements about chemical equilibrium is correct?

Accepted Answer

At equilibrium, the forward and reverse reactions occur at the same rate.

Question 19

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

Accepted Answer

Radioactive isotopes can be used as tracers to track atoms through metabolism.

Chapter 2: The Chemical Context of Life – Study Notes

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