Campbell's Biology 9e - Chapter 2: The
Chemical Context of Life (Test Bank)
About 25 of the 92 natural elements are known to be essential to life. Which four of these 25
elements make up approximately 96% of living matter? - ANS carbon, hydrogen, nitrogen,
oxygen
Trace elements are those required by an organism in only minute quantities. Which of the
following is a trace element that is required by humans and other vertebrates, but not by other
organisms such as bacteria or plants? - ANS iodine
Which of the following statements is false? - ANS Virtually all organisms require the same
elements in the same quantities.
What factors are most important in determining which elements are most common in living
matter? - ANS both the relative abundances of the elements and the emergent properties of the
compounds made from these elements
Why is each element unique and different from other elements in chemical properties? - ANS
Each element has a unique number of protons in its nucleus.
Knowing just the atomic mass of an element allows inferences about which of the following? -
ANS the number of protons plus neutrons in the element
In what way are elements in the same column of the periodic table the same? - ANS They have
the same number of electrons in their valence shell.
Oxygen has an atomic number of 8 and a mass number of 16. Thus, what is the atomic mass of
an oxygen atom? - ANS approximately 16 daltons
The nucleus of a nitrogen atom contains 7 neutrons and 7 protons. Which of the following is a
correct statement concerning nitrogen? - ANS The nitrogen atom has a mass number of 14 and
an atomic mass of approximately 14 daltons.
Molybdenum has an atomic number of 42. Several common isotopes exist, with mass numbers
of 92, 94, 95, 96, 97, 98, and 100. Therefore, which of the following can be true? - ANS
Molybdenum atoms can have between 50 and 58 neutrons.
Carbon-12 is the most common isotope of carbon, and has an atomic mass of 12 daltons. A
mole of carbon in naturally occurring coal, however, weighs slightly more than 12 grams. Why? -
ANS Some carbon atoms in nature have more neutrons.
, Which of the following best describes the relationship between the atoms described below? -
ANS They are isotopes.
The precise weight of a mole of some pure elements like silicon (Si) can vary slightly from the
standard atomic mass, or even from sample to sample. Why? - ANS The element may have
multiple stable isotopes, and the isotopic composition may vary from sample to sample.
One difference between carbon-12 (12-6-C) is that carbon-14 (14-6-C) has - ANS two more
neutrons than carbon-12.
An atom has 6 electrons in its outer shell. How many unpaired electrons does it have? - ANS 2
The atomic number of nitrogen is 7. Nitrogen-15 is heavier than nitrogen-14 because the atomic
nucleus of nitrogen-15 contains how many neutrons? - ANS 8
Electrons exist only at fixed levels of potential energy. However, if an atom absorbs sufficient
energy, a possible result is that - ANS an electron may move to an electron shell farther away
from the nucleus.
The atomic number of neon is 10. Therefore, which of the following is most correct about an
atom of neon? - ANS It has 8 electrons in its outer electron shell and it is inert.
From its atomic number of 15, it is possible to predict that the phosphorus atom has - ANS 15
protons and 15 electrons.
Atoms whose outer electron shells contain 8 electrons tend to - ANS be both chemically inert
and gaseous at room temperature.
The atomic number of each atom is given to the left of each of the elements below. Which of the
atoms has the same valence as carbon (12-6-C)? - ANS 14Si silicon
Two atoms appear to have the same mass number. These atoms - ANS must have the same
number of protons + neutrons.
Fluorine has an atomic number of 9 and a mass number of 19. How many electrons are needed
to complete the valence shell of a fluorine atom? - ANS 1
What is the maximum number of electrons in a single 2 p orbital of an atom? - ANS 2
The organic molecules in living organisms have a measurably lower ratio of
carbon-13/carbon-12, two stable isotopes of carbon that comprise approximately 1.1% and
98.9% of atmospheric carbon, respectively. What is a reasonable explanation for this
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