뒤로Chapter 2: The Chemical Context of Life – Study Notes
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Chapter 2: The Chemical Context of Life
Matter
Matter is the foundation of all biological systems, encompassing everything that occupies space and has mass. Understanding matter is essential for studying the chemical basis of life.
Definition: Matter is anything that takes up space and has mass.
Composition: Matter consists of chemical elements in pure form, or mixtures of elements and chemical compounds.
Elements: An element is a substance that cannot be broken down to other substances by chemical reactions.
Compounds: A compound is a substance consisting of two or more elements in a fixed ratio.
Elements and Compounds
Elements and compounds are the basic chemical substances that make up all matter.
Element: A pure substance that cannot be transformed into other substances by chemical reactions. Example: Iron (Fe) is one of the 92 naturally occurring elements.
Compound: Composed of two or more elements (e.g., water, H2O). Compounds have characteristics different from their constituent elements.
Emergent Properties: Compounds often exhibit properties distinct from those of the individual elements that compose them.
Compounds
Compounds are formed by the chemical combination of elements in specific ratios, resulting in substances with unique properties.
Fixed Ratio: Compounds consist of elements combined in a fixed ratio. Example: Sodium chloride (NaCl) contains equal numbers of sodium and chlorine atoms.
Emergent Properties: Pure sodium is a metal, and chlorine is a gas, but together they form edible table salt, which has properties not found in either element alone.
Example: The combination of sodium and chlorine to form NaCl demonstrates how chemical bonding creates new substances with novel characteristics.
Elements of Life
Only a small subset of elements are essential for life, and these elements are found in all living organisms.
Essential Elements: About 20–25% of the 92 naturally occurring elements are essential for life.
Major Elements: Carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) make up approximately 96% of living matter.
Other Important Elements: The remaining 4% consists mainly of calcium (Ca), phosphorus (P), potassium (K), and sulfur (S).
Trace Elements: Required by organisms in minute quantities (e.g., iron, iodine, zinc).
Table: Elements in the Human Body
Element | Symbol | Percentage of Body Mass (including water) |
|---|---|---|
Oxygen | O | 65.0% |
Carbon | C | 18.5% |
Hydrogen | H | 9.5% |
Nitrogen | N | 3.3% |
Calcium | Ca | 1.5% |
Phosphorus | P | 1.0% |
Potassium | K | 0.4% |
Sulfur | S | 0.3% |
Sodium | Na | 0.2% |
Chlorine | Cl | 0.2% |
Magnesium | Mg | 0.1% |
Trace elements (less than 0.01% of mass): Boron (B), chromium (Cr), cobalt (Co), copper (Cu), fluorine (F), iodine (I), iron (Fe), manganese (Mn), molybdenum (Mo), selenium (Se), silicon (Si), tin (Sn), vanadium (V), zinc (Zn).
Atomic Structure
Atoms are the smallest units of matter that retain the properties of an element. Understanding atomic structure is fundamental to the study of chemistry and biology.
Atom: The smallest unit of matter that retains the properties of an element.
Subatomic Particles: Atoms are composed of protons (positive charge), neutrons (no charge), and electrons (negative charge).
Nucleus: Protons and neutrons form the atomic nucleus; electrons form a cloud around the nucleus.
Unique Number: Each element has a unique number of protons, known as its atomic number.
Additional info: The arrangement of electrons in shells and orbitals determines the chemical behavior of atoms, which is covered in further detail in subsequent sections of the chapter.
