Question 1

Which of the following elements is NOT one of the six principal chemical elements of life?

Accepted Answer

Calcium (Ca)

Question 2

How many valence electrons does a nitrogen atom have?

Accepted Answer

$$5$$

Question 3

Which statement best explains why water is a polar molecule?

Accepted Answer

Oxygen is more electronegative than hydrogen, creating partial charges on the molecule.

Question 4

Which type of chemical bond involves the sharing of electrons between two non-metal atoms?

Accepted Answer

Covalent bond

Question 5

What is the main reason oil and water do not mix, even after vigorous shaking?

Accepted Answer

Oil molecules are nonpolar and cannot form hydrogen bonds with water.

Question 6

Which of the following best describes a hydrogen bond?

Accepted Answer

An attraction between a partially positive hydrogen atom and a partially negative atom in another molecule.

Question 7

Why does ice float on liquid water?

Accepted Answer

Hydrogen bonding causes water molecules in ice to form a lattice that is less dense than liquid water.

Question 8

Which of the following molecules is most likely to dissolve in water?

Accepted Answer

A polar molecule with partial charges

Question 9

A molecule of ammonia ($$NH_3) $$can form hydrogen bonds with water. Which property of ammonia allows this?

Accepted Answer

Ammonia has a polar covalent bond and a lone pair on nitrogen.

Question 10

Which of the following best explains why water has a high specific heat capacity?

Accepted Answer

Hydrogen bonds between water molecules require a lot of energy to break.

Question 11

Which of the following statements about electronegativity is TRUE?

Accepted Answer

Electronegativity increases from left to right and from bottom to top on the periodic table.

Question 12

Which of the following is a consequence of water's high surface tension?

Accepted Answer

Small insects can walk on the surface of water without sinking.

Question 13

A student claims that sodium chloride ($$NaCl) $$dissolves in water because both are nonpolar. What is the error in this statement?

Accepted Answer

Water is polar and $$NaCl is $$ionic; water's partial charges attract the ions.

Question 14

Which of the following best describes a hydrophobic molecule?

Accepted Answer

A molecule that is uncharged and nonpolar, repelling water.

Question 15

Which of the following molecules can form the greatest number of hydrogen bonds with neighboring water molecules?

Accepted Answer

A single water molecule ($$H_2O)$$

Question 16

Which of the following best explains why sweating cools the human body?

Accepted Answer

Evaporation of water requires energy to break hydrogen bonds, removing heat from the skin.

Question 17

Which of the following molecules is most likely to be amphipathic (having both hydrophilic and hydrophobic regions)?

Accepted Answer

A phospholipid

Question 18

If an atom has 6 valence electrons, how many unpaired valence electrons does it have?

Accepted Answer

$$2$$

Question 19

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

Accepted Answer

A polar covalent bond has unequal sharing of electrons due to differences in electronegativity.

Question 20

Which element is the most electronegative among the following?

Accepted Answer

Fluorine (F)

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

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