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Bio Chapter 2 Outline - Campbell and Reece Chapter 2 1 The...

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Campbell and Reece Chapter 2 1 The Chemical Context of Life I. Atoms and Molecules Matter - anything that takes up space and has mass. Matter is composed of elements. Element - a substance that can not be broken down to other substances by chemical reactions. In other words, an element is composed of a single type of Atom (i.e., the smallest unit of matter having the physical and chemical properties of an element). Major elements 70 - 95% of all cells is water (H 2 O) 96% of living matter is made up of C, H, O, and N. other major elements include P, S, K, Ca, Mg, Na, Cl Trace elements - required in minute quantities (< 0.01%) but are nonetheless essential for life e.g., Fe, Zn, I, Mn, V… Compounds - Elements are organized into compounds two or more elements combined in a fixed ratio. 1. Atomic structure Atoms are mostly space - they have a dense nucleus and a large amount of empty space occupied by scattered electrons Atoms are composed of three stable subatomic particles. Charge Mass (g) nucleus protons (p) +1 1.7 x 10 -24 ~1 Da (dalton)* neutrons (n) 0 1.7 x 10 -24 ~1 Da electrons (e - ) -1 0.0005 x mass of a proton or neutron Note: the mass of e - is ignored in computing total mass of an atom * Dalton is equivalent to an atomic mass unit (amu) Notation (mass number = sum of protons and neutrons) atomic mass 16 O Element symbol atomic number 8 (number of protons) (If the atom has a neutral charge then atomic number = the number of electrons)
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Campbell and Reece Chapter 2 2 All atoms of an element have the same number of protons, however, the mass of some atoms of an element can vary (i.e., some atomic forms have more neutrons than others). These different forms are called isotopes e.g., C - atomic mass of 12, 13, 14 P - atomic mass of 31, 32, 33 Isotopes are considered stable if their nuclei do not have a tendency to lose particles. Radioactive isotopes are unstable and their nuclei decay or give off particles and energy. Radioactive isotopes are used in medicine, research, energy, bombs II. Electrons - Shells, Energy Levels and Chemical Properties The distance of an electron from the nucleus is determined by its energy level
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