After studying this chapter, you should be able to:
After studying this chapter, you should be able to:
Identify the elements common in biological matter
Explain the structure and components of an atom
Identify the properties of elements given a periodic table
Define the term isotope and explain how isotopes are used in radiometric dating
State the first and second laws of thermodynamics
Explain the difference between kinetic and potential energy
Elements in Biological Matter
The environment is composed of matter and energy, from the molecules that make up a tree’s cells to the fire that burns down a forest. Understanding environmental issues requires knowledge of chemistry, which is the study of how matter and energy interact.
At its most fundamental level, life is made up of matter. Matter is any substance that occupies space and has mass. Elements are unique forms of matter with specific chemical and physical properties that cannot be broken down into smaller substances by ordinary chemical reactions. There are 118 elements, but only 92 occur naturally. The remaining elements are synthesized in laboratories and are unstable.
Each element is designated by its chemical symbol, which is a single capital letter or, when the first letter is already “taken” by another element, a combination of two letters. Some elements follow the English term for the element, such as C for carbon and Ca for calcium. Other elements’ chemical symbols derive from their Latin names; for example, the symbol for sodium is Na, referring to natrium, the Latin word for sodium.
The four elements common to all living organisms are oxygen (O), carbon (C), hydrogen (H), and nitrogen (N). In the non-living world, elements are found in different proportions, and some elements common to living organisms are relatively rare on the earth as a whole, as shown in Table 1. For example, the atmosphere is rich in nitrogen and oxygen but contains little carbon and hydrogen, while the earth’s crust, although it contains oxygen and a small amount of hydrogen, has little nitrogen and carbon. In spite of their differences in abundance, all elements and the chemical reactions between them obey the same chemical and physical laws regardless of whether they are a part of the living or non-living world.
Table 1. Approximate Percentage of Elements in Living Organisms Compared to the Non-living World
Element
Living Organisms
Atmosphere
Earth’s Crust
Oxygen (O)
65%
21%
46%
Carbon (C)
18%
trace
trace
Hydrogen (H)
10%
trace
0.1%
Nitrogen (N)
3%
78%
trace
Atoms
To understand how elements come together, we must first discuss the smallest component or building block of an element, the atom. An atom is the smallest unit of matter that retains all of the chemical properties of an element. For example, one gold atom has all of the properties of gold in that it is a solid metal at room temperature. A gold coin is simply a very large number of gold atoms molded into the shape of a coin and containing small amounts of other elements known as impurities. Gold at