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Science and Society

Who Has the Right?

s the population grows and new dustrial interests claim they should have QUESTIONS TO DISCUSS
Aindustries develop, more and more the water because they create jobs and
demands are placed on the water supply. products that people must have. Cities, on 1. Who should have the first priority for
This raises some issues about how water the other hand, claim that domestic con- water use?
should be divided among agriculture, in- sumption is the most important because 2. Who should have the last priority for
dustries, and urban domestic use. Agri- people cannot survive without water. Yet water use?
cultural interests claim they should have others claim that no group has a right to
3. What determined your answers to
the water because they produce the food use water when it is needed to maintain
questions 1 and 2?
and fibers that people must have. In- habitats.

Negative oxygen end Oxygen atom

Hydrogen bond
A Positive hydrogens

Hydrogen atom

FIGURE 11.3 The hexagonal structure of ice. Hydrogen bond-
ing between the oxygen atom and two hydrogen atoms of other
water molecules results in a tetrahedral arrangement, which forms
Hydrogen bonds
the open, hexagonal structure of ice. Note the angles of the water
molecules do not change but have different orientations.

B bond, a hydrogen-oxygen bond, or a hydrogen-nitrogen bond.
However, for brevity the second part of the bond is not named
FIGURE 11.2 (A) The water molecule is polar, with centers
of positive and negative charges. (B) Attractions between these and all the hydrogen-something bonds are simply known as hy-
positive and negative centers establish hydrogen bonds between drogen bonds. The dotted line between the hydrogen and oxy-
adjacent molecules. gen molecules in Figure 11.2B represents a hydrogen bond. A
dotted line is used to represent a bond that is not as strong as
the bond represented by the solid line of a covalent compound.
A water molecule has a negative center at the oxygen end Hydrogen bonding accounts for the physical properties of
and a positive center at the hydrogen end. The positive charges water, including its unusual density changes with changes in
on the hydrogen end are separated, giving the molecule a bent temperature. Figure 11.3 shows the hydrogen-bonded structure
rather than straight-line arrangement. Figure 11.2A shows a of ice. Water molecules form a six-sided hexagonal structure
model of a water molecule showing its polar nature. that extends out for billions of molecules. The large channels, or
It is the polar structure of the water molecule that is respon- holes, in the structure result in ice being less dense than water.
sible for many of the unique properties of water. Polar molecules The shape of the hexagonal arrangement also suggests why
of any substances have attractions between the positive end of a snowflakes always have six sides. Why does it seem as if no two
molecule and the negative end of another molecule. When the snowflakes are alike? Perhaps the answer can be found in the
polar molecule has hydrogen at one end and fluorine, oxygen, or almost infinite variety of shapes that can be built from billions
nitrogen on the other, the attractions are strong enough to make and billions of tiny hexagons of ice crystals.
a type of bonding called hydrogen bonding. Hydrogen bond- When ice is warmed, the increased vibrations of the mol-
ing is a strong bond that occurs between the hydrogen end of a ecules begin to expand and stretch the hydrogen bond struc-
molecule and the fluorine, oxygen, or nitrogen end of similar ture. When ice melts, about 15 percent of the hydrogen bonds
molecules. A better name for this would be a hydrogen-fluorine break and the open structure collapses into the more compact

278 CHAPTER 11 Water and Solutions 11-4