Page 44 - Environment: The Science Behind the Stories

Addition of (Figure 2.3b). Ions are denoted by their elemental symbol fol-
1 neutron lowed by their ionic charge. For instance, a common ion used
2+
2
(a) Hydrogen isotope, H by mussels and clams to form shells is Ca , a calcium atom
Protons = 1 that has lost two electrons and thus has a charge of positive
Electrons = 1 2. The damaging radiation emitted by radioisotopes is called
– Neutrons = 1 ionizing radiation because it generates ions when it strikes
molecules, and these ions affect the stability and functionality
of biological molecules.
–
Hydrogen atom, H (b) Hydrogen ion, H + Atoms bond to form molecules
Protons = 1 Protons = 1 and compounds
Electrons = 1 Electrons = 0
Neutrons = 0 Neutrons = 0 Atoms can bond together and form molecules, combinations
of two or more atoms. Common molecules containing only
Loss of a single element include those of hydrogen (H ) and oxygen
1 electron 2
(O ), each of which exists as a gas at room temperature. A
2
Figure 2.3 Hydrogen has a mass number of 1 because a molecule composed of atoms of two or more different ele-
typical atom of this element contains one proton and no ments is called a compound. One compound is water; it is
2
neutrons. Deuterium (hydrogen-2 or H), an isotope of hydrogen composed of two hydrogen atoms bonded to one oxygen
(a), contains a neutron as well as a proton and thus has greater atom, and it is denoted by the chemical formula H O. Another
mass than a typical hydrogen atom; its mass number is 2. The 2
+
hydrogen ion, H (b), occurs when an electron is lost; it therefore compound is carbon dioxide, consisting of one carbon atom
has a positive charge. bonded to two oxygen atoms; its chemical formula is CO .
2
Atoms bond together because of an attraction for one
another’s electrons. Because the strength of this attraction var-
FAQ When something is irradiated, does it ies among elements, atoms may be held together in different
become radioactive?
Thanks to comic books and movies, many people believe that ways. When electrons are shared between atoms, a covalent
bond forms. For example, two atoms of hydrogen share elec-
when an organism is exposed to high-energy radiation from trons equally as they bind together to form hydrogen gas, H .
2
a source outside the body, such as the sun or nuclear waste, However, in a water molecule, oxygen attracts shared electrons
the organism becomes a source of ionizing radiation—that is, more strongly than does hydrogen. The result is that water has
it becomes “radioactive.” In reality, this does not happen. a partial negative charge at its oxygen end and partial positive
An irradiated organism suffers damage from radiation, charges at its hydrogen ends. This arrangement allows water
but it does not absorb the ionizing radiation, store it, and then molecules to adhere to one another in a type of weakly attrac-
re-emit it to the environment. The radiation simply enters the tive interaction called a hydrogen bond (Figure 2.4). CHAPTER 2 • E ART h’s Physi CAL
organism’s cells, causes damage, and passes through the In compounds in which the strength of attraction is suffi-
organism. So even after experiencing substantial impacts from ciently unequal, an electron may be transferred from one atom
radiation poisoning, the organism is no more radioactive than it to another. This creates oppositely charged ions that form ionic
was before exposure because it was only exposed to radiation
(a form of energy) and was not contaminated with radioactive
particles (a form of matter) that emit harmful radiation.
The damaging effects of ionizing radiation can be put
to positive use, though. Radiation has been used to sterilize
medical supplies since the 1950s to prevent patients from (–)
receiving secondary infections while in the hospital. Raw meat Hydrogen bond
can also be irradiated to kill harmful microbes that may be lurk- (+) Hydrogen atom
ing within the meat, such as Salmonella or disease-causing
strains of Escherichia coli (E. coli). In both cases, the irradi- Water molecule H Oxygen atom s ys TE m s: mATTER , E NER gy, AN d
ated material does not become radioactive, just free of living Hydrogen atom
microorganisms or viruses that could cause sickness or death. (–) O H
(+) (+)
(–) (–)

of about 700 million years. Radioisotopes released into the (+) Covalent bond
environment from the Fukushima nuclear power plant acci-
dent included iodine-131 (half-life of 8 days), cesium-134
(half-life of 2 years), and cesium-137 (half-life of 30 years), gE o L ogy
showing the long-term implications of nuclear accidents.
Figure 2.4 By enabling water molecules to adhere loosely
Ions Atoms may also gain or lose electrons, thereby becom- to one another, hydrogen bonds give water several unique
ing ions, electrically charged atoms or combinations of atoms properties crucial for life. 43

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