Question 1

Which of the following elements makes up the largest percentage of living matter?

Accepted Answer

Oxygen

Question 2

A molecule of water ($$\mathrm{H_2O}) is $$held together by which type of bond between its atoms?

Accepted Answer

Covalent bond

Question 3

Which of the following best explains why water is a polar molecule?

Accepted Answer

Oxygen is more electronegative than hydrogen, causing unequal sharing of electrons

Question 4

Which of the following is a correct statement about the cycling of elements in ecosystems?

Accepted Answer

Carbon and nitrogen are both cycled through ecosystems

Question 5

What is the main reason that nitrogen is considered a limiting factor for life on Earth?

Accepted Answer

Nitrogen is required for building proteins and nucleic acids, but is not easily accessible to most organisms

Question 6

Which of the following best describes a hydrogen bond?

Accepted Answer

A bond formed when a hydrogen atom covalently bonded to one electronegative atom is attracted to another electronegative atom

Question 7

Which of the following molecules is most likely to be hydrophobic?

Accepted Answer

A molecule with mostly nonpolar covalent bonds

Question 8

If an atom has 6 protons, 6 neutrons, and 6 electrons, what element is it and how many valence electrons does it have?

Accepted Answer

Carbon, 4 valence electrons

Question 9

Which of the following best describes the octet rule?

Accepted Answer

Atoms are stable when they have 8 electrons in their valence shell

Question 10

Which of the following is true about the chemical behavior of polar and nonpolar groups in water?

Accepted Answer

Polar groups are hydrophilic and dissolve in water

Question 11

Which of the following is a correct example of an ionic bond?

Accepted Answer

The bond formed when sodium transfers an electron to chlorine, forming $$\mathrm{Na^+}$$ and $$\mathrm{Cl^-}$$

Question 12

Which of the following statements about valence electrons is correct?

Accepted Answer

The number of valence electrons determines how an atom bonds with other atoms

Question 13

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

Accepted Answer

The shape affects the molecule's function and ability to interact with other molecules

Question 14

Which of the following is true about chemical reactions?

Accepted Answer

Chemical reactions involve both the making and breaking of chemical bonds

Question 15

A molecule contains a region with a partial negative charge and a region with a partial positive charge. What type of bond is most likely present?

Accepted Answer

Polar covalent bond

Question 16

Which of the following is NOT an essential element for life, making up more than 96% of living matter?

Accepted Answer

Sulfur

Question 17

Which of the following best describes the difference between a covalent and an ionic bond?

Accepted Answer

Covalent bonds involve sharing electrons, ionic bonds involve transfer of electrons

Question 18

Which of the following is a real-world example of a molecule whose function depends on its shape?

Accepted Answer

Endorphin binding to brain cell receptors

Question 19

Which of the following statements about electronegativity is correct?

Accepted Answer

Electronegativity describes how strongly an atom attracts electrons in a bond

Question 20

Which of the following best explains why 'like dissolves like' in chemistry?

Accepted Answer

Polar substances dissolve in polar solvents due to similar charge distributions

Unit 1: The Chemistry of Life – Elements, Molecules, and Chemical Bonds

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