Chapter 2: The Chemical Context of Life
The compound CaSO4 ionizes into a calcium ion and a sulfate ion (SO4). Calcium has two electrons in its outer shell. Upon ionization, what would you expect the charge on the sulfate ion to be? (Concept 2.3)
-2
The most common form of calcium has 20 protons, 20 neutrons, and 20 electrons. Which of the following elements would be an isotope of calcium? (Concept 2.2)
an atom with 20 protons, 21 neutrons, and 20 electrons
In which of the following will isotopes of an element always differ? (Concept 2.2)
atomic mass
Ionic bonds form as a result of __________. (Concept 2.3)
attraction between ions that have opposite charges
Why are radioactive isotopes useful in scientific research? (Concept 2.2)
because they can be used as tracers to follow particular atoms and molecules through metabolic pathways
Pharmaceutical researchers are often interested in blocking particular receptor proteins on cell surfaces. What chemical property of a molecule would be most important for this type of application? (Concept 2.3)
the molecule's shape
Phosphorus-32 (radioactive) has __________ than phosphorus-35 (normal). (Concept 2.2)
three fewer neutrons
When do hydrogen bonds occur? (Concept 2.3)
when partial opposite charges on molecules come close enough to attract each other
For most atoms, when is an unreactive configuration of electrons attained? (Concept 2.2)
when the atom has eight electrons in its outermost shell
A covalent bond is likely to be polar if __________. (Concept 2.3)
one of the atoms sharing electrons is much more electronegative than the other
Which of the following is a trace element? (Concept 2.1)
Copper
When one or more pairs of valence electrons are shared by two neutral atoms, what type of bond is formed? (Concept 2.3)
a covalent bond
How many electrons would be present in the valence shell of a sulfur atom (atomic number 16, mass number 32)? (Concept 2.2)
6
A neutral atom of chlorine has an atomic number of 17. It has __________ electrons in its third shell. (Concept 2.2)
7
An element has eight protons, nine neutrons, and eight electrons. Its atomic number and atomic mass, respectively, are __________. (Concept 2.2)
8 and 17.
A particular carbon isotope has an atomic number of 6 and an atomic mass of 14. The respective number of neutrons, protons, and electrons that this carbon isotope has is __________. (Concept 2.2)
8, 6, and 6
There are __________ naturally occurring elements. (Concept 2.1)
92
What is generally true about essential elements and living organisms? (Concept 2.1)
Although all forms of life require iron, other elements are required only by certain species.
What is the role of van der Waals interactions in biological molecules? (Concept 2.3)
Although they are weak bonds, van der Waals interactions help to reinforce the three-dimensional shapes of large molecules.
Which of the following has negligible mass? (Concept 2.2)
Electron
How would you respond to this reasoning: oxygen is not a greenhouse gas; therefore, gases containing oxygen—such as ozone, nitrous oxide, and carbon dioxide—are not greenhouse gases either.(Concept 2.1)
False. Compounds can have emergent properties that are very different from those of the elements that form them.
If you were told that concentrations of trace elements above what is required by organisms generally have no effect on those organisms, what would you say? (Concept 2.1)
False. Elevated concentrations of some trace elements such as cobalt and chromium can be toxic.
Which of the following subatomic particles has appreciable mass but no charge? (Concept 2.2)
Neutron
Copper has an atomic number of 29 and a mass number of 64. What would result if an uncharged copper atom lost two electrons? (Concept 2.3)
The atomic number would remain 29, the mass number would remain 64, and the atom would be a cation with a +2 charge.
Which statement describes a reversible reaction that has reached chemical equilibrium? (Concept 2.4)
The rate of the reverse reaction equals the rate of the forward reaction.
Which statement is true about chemical reactions? (Concept 2.4)
They involve the making and breaking of chemical bonds.
An atom that normally has __________ in its outer shell would NOT tend to form chemical bonds with other atoms. (Concept 2.2)
eight electrons
The number of protons in an uncharged atom __________. (Concept 2.2)
equals the number of electrons.
What are the four most abundant elements found in living systems? (Concept 2.1)
hydrogen, oxygen, nitrogen, and carbon
A hydrogen bond __________. (Concept 2.3)
is a weak chemical bond.
When the proton number and electron number are unequal, the atom or molecule __________. (Concept 2.3)
is an ion
Which molecule has the shape of a completed tetrahedron? (Concept 2.3)
methane (CH4)
The chemical characteristics or reactivity of an element depend mostly on the __________. (Concept 2.2)
number of electrons in its outermost shell
Some groups of chemical elements react similarly to one another. For example, the chemistries of sodium and of lithium are similar, as are the chemistries of chlorine and of iodine. These similarities in chemistry result when different elements have similar __________. (Concept 2.2)
numbers of outer-shell electrons
An uncharged atom of nitrogen (atomic number = 7) has __________. (Concept 2.2)
seven protons and seven electrons