Biol 131
Question bank
Nature of Molecules
You are expected to bring completed study questions to the evening study session. Answer
these study questions by referencing the relevant sections of the textbook. The written
explanations are the most important part of your answers and key to learning of concepts.
Use these tables as necessary to answer questions:
Elec. Neg.
0.82
0.93
1
1.55
1.83
2.19
2.2
2.55
2.58
3.04
3.16
3.44
3.98
Name
Potassium
Sodium
Calcium
Manganese
Iron
Phosphorus
Hydrogen
Carbon
Sulfur
Nitrogen
Chlorine
Oxygen
Fluorine
Common ion
K+
Na+
Ca2+
Mn+
Fe3+
P
H
C
S
N
ClOF-
1. A carbon atom contains six protons and six neutrons.
A. Its atomic number is ____ and its atomic weight is _____.
B. How many electrons does it have? _____
C. How many more electrons must it have to fill its outermost shell? _____
D. Carbon with an atomic weight of 14 is radioactive. How does it differ in structure from
nonradioactive carbon? __________________________________
How does this difference affect its chemical behavior?
2. The electrons in the K level electron shell of a nitrogen atom (see
figure) participate in chemical bonding.
True
False
Explain why or why not.
3. The difference in ______________________ between atoms determines how polar a
covalent bond between them will be. Would you expect the covalent bond between a
hydrogen and nitrogen to be more or less polar (circle) than the covalent bond between
hydrogen and oxygen?
Explain your answer.
Biol 131
Question Bank
Molecular Structure
Page 1
4. Which of the following pairs of elements are likely to form ionic bonds?
A. Hydrogen and carbon
D. Sulfur and hydrogen
B. Potassium and chlorine
E. Carbon and chlorine
C. Carbon and oxygen
Explain why:
5. Referring to the molecular model below …
A. Draw in a ‘C’ wherever the model implies the position of a carbon atom. How many
carbon atoms does the molecule have? _____
B. Add covalently bonded ‘H’s wherever a hydrogen is needed to complete octets on the
carbon atoms. How many hydrogen atoms? _____
6. Which of the following pairs of atoms do you expect to be least reactive?
A. argon and neon
C. sodium and sulfur
B. hydrogen and oxygen
D. helium and magnesium
This is due to the:
A. differences in their electronegativities
B. number of valence electrons
C. size of the atoms
Explain:
7. The half-life of Carbon-14 is approximately 5,600 years. Using this information scientists
have been able to determine the age of some artifacts left by humans. Suppose that a scientist
wanted to know approximately how old a piece of wood was that she found on the floor in an
old cave that had recently been discovered. She removed the wood (with permission) to her
laboratory. If a similar sized piece of wood that was just taken from a tree has 8 grams of
Carbon 14 and the piece of wood from the cave contains only 2 grams of Carbon-14, how old
is the wood from the cave?
A. 5,600 years
D. 22,400 years
B. 11,200 years
E. 28,000 years
C. 16,800 years
Show your calculations here
Biol 131
Question Bank
Molecular Structure
Page 2
8. Referring to the water molecule to the right. . .
A. Indicate the presence of partial positive and
negative charges using the symbols δ+ and δ–.
B. Assuming a hydrogen atom can participate in a
single hydrogen bond, and an oxygen atom can
form two hydrogen bonds, add to the diagram as
many other water molecules as will hydrogen
bond to this one. Draw dashed lines (- - - )
showing the H-bonds.
C. This shows that each water molecule can H-bond
with up to ___ neighboring water molecules.
9. Like oxygen, sulfur can form covalent bonds with two hydrogens to form the molecule H2S
(hydrogen sulfide – a substance with a notable ‘rotten egg’ smell). At common temperatures,
H2S exists normally as a gas, whereas H2O exists as a liquid.
A. What are the electronegativities of H (_____), O (______) and S (_____)?
B. In which molecule will the bonds be most polar, H2S or H2O (circle)?
Explain:
C. Explain how/why the above information explains the tendency of H2S or H2O to exist as a
liquid or a gas:
10. With no active pumping system, water moves up plant stems and trunks of even the tallest
trees. As water evaporates from the leaves more water is ‘pulled’ upward through tiny tubeshaped cells called tracheids, and in doing so brings various mineral nutrients up from the
roots. Explain how each of the following properties of water contributes to this process (do
not simply define the terms).
Adhesion:
Cohesion:
High solubility:
Biol 131
Question Bank
Molecular Structure
Page 3
11. A classmate makes the following claims -- explain why each statement is wrong.
1) “Pure water lacks free H+ and OH-.”
2) “The concentration of H+ increases as the pH increases.”
3) “The concentration of OH- increases as the pH decreases.”
4) “The concentrations of H+ at pH 5 is 2X greater than that at pH 6.”
5) “The effect of a pH buffer is to stabilize the pH of water at 7.”
12. Your dog becomes ill and you rush him to the veterinarian’s office. A technician draws blood
from your dog’s leg for a lab test that has been ordered by the vet. After a few minutes the
lab results are given to the vet. The vet grabs a bottle from a shelf and begins to fill a syringe
with a fluid. You inquire about the fluid. The vet says your dog is in acute acidosis and needs
an immediate injection to correct the condition. You know that:
A. your dog’s blood pH has moved toward the acidic end of the pH scale and has a higher
pH value than normal
B. your dog’s blood pH has moved toward the acidic end of the pH scale and has a lower
pH value than normal
C. your dog’s blood pH has moved toward the basic end of the pH scale and has a higher
pH value than normal
D. your dog’s blood pH has moved toward the basic end of the pH scale and has a lower
pH value than normal
13. As you and a friend are entering a chemistry laboratory at your university, you see a sign that
states in big, bold, red letters: DANGER—RADIOACTIVE ISOTOPES IN USE. Your
friend is an accounting major and has not had any science courses yet. She asks you what a
radioactive isotope is and you respond correctly using which of the following choices.
A. Radioactive isotopes are atoms formed by the joining together of two other atoms.
B. Radioactive isotopes are atoms that have a positive or negative charge due to the
presence or absence of electrons.
C. Radioactive isotopes are atoms that are unstable due to the number of neutrons they
possess, and decay by releasing energy and/or particles.
D. Radioactive isotopes are atoms that are more highly reactive in chemical processes due
to the number of electrons they possess.
Biol 131
Question Bank
Molecular Structure
Page 4
14. Would you expect the surface of a water strider’s feet (see figure 2.13 of the textbook) to be
coated with polar or non-polar compounds (circle)? Explain your answer.
15. In the table below, indicate if, and if so explain how, orientation of electron orbitals, number
of valence electrons, and differences in atom electronegativities are relevant to the formation
of covalent, ionic, and hydrogen bonds.
Orientation of
electron orbitals
Number of
valence electrons
Electronegativity
differences
Is / is not (circle) relevant.
Is / is not (circle) relevant.
Is / is not (circle) relevant.
If so, explain:
If so, explain:
If so, explain:
Is / is not (circle) relevant.
Is / is not (circle) relevant.
Is / is not (circle) relevant.
If so, explain:
If so, explain:
If so, explain:
Is / is not (circle) relevant.
Is / is not (circle) relevant.
Is / is not (circle) relevant.
If so, explain:
If so, explain:
If so, explain:
Covalent
bonds
Ionic
bonds
Hydrogen
bonds
Biol 131
Question Bank
Molecular Structure
Page 5