NAME____________________________ DATE______________CLASS_________
Homework/Test
Objectives:
Discuss the properties of hydrogen bonds and their
importance to life.
Standard:
Understand
the structure and function of hydrogen bonds
Sub-objectives:
new scientific discoveries about hydrogen bonds
THE
UNUSUAL PROPERTIES OF WATER
One
of the most important components of life as we know it is the hydrogen bond. It
occurs in many biological structures, such as DNA. But perhaps the simplest
system in which to learn about the hydrogen bond is water. In liquid water and
solid ice, the hydrogen bond is simply the chemical bond that exists between H2O
molecules and keeps them together. Although relatively feeble (about 5%
of a covalent bond), hydrogen bonds are so plentiful in water that they play a
large role in determining their properties.
Arising
from the nature of the hydrogen bond and other factors, such as the disordered
arrangement of hydrogen in water, the unusual properties of H2O have
made conditions favorable for life on Earth. For instance, it takes a relatively
large amount of heat to raise water TEMPERATURE one degree. This enables
the world's oceans to store enormous amounts of heat, producing a moderating
effect on the world's climate, and it makes it more difficult for marine
organisms to destabilize the temperature of the ocean environment even as
their metabolic processes produce copious amounts of waste heat.
In
addition, liquid water expands when cooled below 4 degrees Celsius. This
explains how ice can sculpt geological features over eons through the process of
erosion. It also makes ice less dense than liquid water, and enables ice to
float on top of the liquid. This property allows ponds to freeze on the top and
has offered a hospitable underwater location for many life forms to
develop on this planet.
TWO
TYPES OF BONDS IN WATER
In
water, there are two types of bonds. Hydrogen bonds are the bonds between water
molecules, while the much stronger "sigma" bonds are the bonds within
a single water molecule. Sigma bonds are strongly "covalent," meaning
that a pair of electrons is shared between atoms. Covalent bonds can only be
described by quantum mechanics, the modern theory of matter and energy at the
atomic scale. In a covalent bond, each electron does not really belong to a
single atom--it belongs to both simultaneously, and helps to fill each
atom's outer "valence" shell of electrons, a situation that makes the
bond very stable.
THE
ELECTROSTATIC NATURE OF THE HYDROGEN BOND
On
the other hand, the much weaker hydrogen bonds that exist between H2O
molecules are principally the electrical attractions between a positively
charged hydrogen atom--which readily gives up its electron in water--and a
negatively charged oxygen atom--which receives these electrons--in a neighboring
molecule. It is now known however that hydrogen bonds between water MOLECULES
would also be affected by the sigma bonds within the water molecules and because
of this the hydrogen bonds cannot be completely be described as electrostatic
bonds anymore. Instead, they take on some of the properties of the highly
covalent sigma bonds--and vice versa. In
a sense, the hydrogen bonds would partially assume the identity of these
covalent bonds!
For many years, many scientists dismissed the possibility that hydrogen bonds in water had significant covalent properties This fact can no longer be dismissed. Not only will it allow researchers in many areas to improve theories of water and the many biological structures such as DNA which possess hydrogen bonds. Improved information on the H-bond may also help us to assume better control of our material world. For example, it may allow nanotechnologists to design more advanced self-assembling materials, many of which rely heavily on hydrogen bonds to put themselves together properly.
Instructions:
Please number
the lines in the article, highlight concepts and terms, and place notes along
the margins. (5 pts.)
Please
write answers to all questions, except multiple choice, on a separate sheet of
paper and incorporate the question in your answers.
the article, page in the text, or other source.
(15 pts)
A.
water is
made up of 2 Hydrogen atoms and 1 Oxygen atom
B.
water is
hydrophobic
C.
liquid
water expands below 4 degrees Celsius
D.
liquid
water captures sunlight
EXTRA
CREDIT:
1. What is
nanotechnology?
2. Who
discovered or created “quantum mechanics”?
ESSAY
QUESTION: (15 pts.)
Write
a one page essay on scientist Linus Pauling and his contribution to the
understanding hydrogen bonds.