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General Chemistry Principles, Patterns, and Applications, 2011

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large amounts of other molecules. For example, vitamin B12 contains a single atom of cobalt, which is essential for its<br />

biological function. If the molecule whose level is controlled by the trace element can regulate the level of another<br />

molecule, <strong>and</strong> more <strong>and</strong> more molecules, then the potential exists for extreme amplification of small variations in the<br />

level of the trace element. One goal of modern chemical research is to elucidate in detail the roles of the essential<br />

elements. In subsequent chapters, we will introduce some results of this research to demonstrate the biological<br />

importance of many of the elements <strong>and</strong> their compounds.<br />

Summary<br />

About 19 of the approximately 115 known elements are essential for humans. Anessential element is<br />

one whose absence results in abnormal biological function or development that is prevented by dietary<br />

supplementation with that element. Living organisms contain relatively large amounts of oxygen, carbon,<br />

hydrogen, nitrogen, <strong>and</strong> sulfur (these five elements are known as the bulk elements), along with sodium,<br />

magnesium, potassium, calcium, chlorine, <strong>and</strong> phosphorus (these six elements are known as<br />

macrominerals). The other essential elements are the trace elements, which are present in very small<br />

quantities. Dietary intakes of elements range from deficient to optimum to toxic with increasing<br />

quantities; the optimum levels differ greatly for the essential elements.<br />

K E Y T A K E A W A Y<br />

<br />

The absence of some elements can result in abnormal biological function or development.<br />

1.9 Essential Skills 1<br />

T O PI C S<br />

<br />

<br />

<br />

<br />

Measurement<br />

Scientific Notation<br />

Significant Figures<br />

Accuracy <strong>and</strong> Precision<br />

This section describes some of the fundamental mathematical skills you will need to complete the questions <strong>and</strong><br />

problems in this text. For some of you, this discussion will serve as a review, whereas others may be encountering at<br />

least some of the ideas <strong>and</strong> techniques for the first time. We will introduce other mathematical skills in subsequent<br />

Essential Skills sections as the need arises. Be sure you are familiar with the topics discussed here before you start<br />

the Chapter 1 "Introduction to <strong>Chemistry</strong>" problems.<br />

Saylor URL: http://www.saylor.org/books<br />

Saylor.org<br />

73

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