Chapter 2 Outline - Summary Campbell Biology PDF

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Chapter 2: The Chemical Context of Life 2.1 “Matter consists of chemical elements in pure form and in combinations called compounds” 

There are 92 elements occurring in nature

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About 25 of the 92 elements are known to be essential to life

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4 elements—Carbon (C), oxygen (O), hydrogen (H), and Nitrogen (N)—make up 96% of living matter

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Phosphorous, sulfur, calcium, potassium, and a few others account for most of other 4%

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Some trace elements, such as iron, are needed by all forms of life; others are required only by certain species

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A daily intake of only 0.15 mg of iodine is adequate for normal activity of the human thyroid

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An iron deficiency in the diet causes the thyroid gland to grow to abnormal size, a condition called goiter 2.2 “An element’s properties depend on the structure of its atoms”

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Each element consists of a certain kind of atom that is different from the atoms of any other element

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Atoms are so small that it would take about a million of them to stretch across the period at the end of this sentence.

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We symbolize atoms with the same abbreviation used for the element made up of those atoms; thus C stands for both the element carbon and a single carbon atom

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Atoms are composed of even smaller parts. 3 of them are neutrons, protons, and electrons

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Neutrons and protons are packed together tightly to form an atomic nucleus

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The electrons, moving nearly at the speed of light, form a cloud around the nucleus

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Electrons (-) and protons (+) are electrically charged

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Neutrons and protons have masses close to 1 dalton, while electrons have a mass ½000th of that

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Atomic number = number of protons (subscript). Atomic mass = protons + neutrons (superscript)

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The most common isotope is carbon-12

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Radioactive carbon decays to nitrogen

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An electron’s energy level is correlated with its average distance from the nucleus; these average distances are represented symbolically by electron shells

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The chemical behavior of an atom is determined by its electron configuration— that is, the distribution of electrons in the atom’s electron shells

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The chemical behavior depends mostly on the number of electrons in its outermost shell, or valence shell. Valence electrons make up valence shells 2.3 “The formation and function of molecules depend on chemical bonding between atoms”

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The strongest kinds of chemical bonds are covalent and ionic bonds

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Covalent- sharing of a pair of valence electrons. Ionic- electrons are transferred

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Two or more atoms held together by covalent bonds constitute a molecule

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Compounds formed by ionic bonds are called salts or ionic compounds

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We know NaCl as table salt

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Most of the strongest chemical bonds in living organisms are covalent ones, which link atoms to form a cell’s molecules

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Several types of chemical bonds, such as ionic and hydrogen bonds, are important in living organisms as well

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A molecule has a characteristic size and shape. The precise shape of a molecule is usually very important to its function in the living cell 2.4 “Chemical reactions make and break chemical bonds”

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Reactants- left side of arrow. Products- right side of arrow

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Opposite headed arrows indicate the reaction is reversible

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The greater the concentration of the reactant molecules, the more frequently they collide with one another and have an opportunity to form products. The same holds for products

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The point at which the reactions offset one another exactly is called chemical equilibrium

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Equilibrium does not mean the reactants and products are equal in concentration, but only that their concentrations have stabilized at a particular ratio...