LIFE 102 Lecture Notes - Atomic Number, Covalent Bond, Valence Electron

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10 May 2014
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About 25 of the 92 elements are essential to life. Carbon, hydrogen, oxygen, and nitrogen make up 96% of living matter. Most of the remaining 4% consists of calcium, phosphorus, potassium, and sulfur. Trace elements are those required by an organism in minute quantities. Neutron mass and proton mass are almost identical and are measured in daltons. Atoms of the various elements differ in number of subatomic particles. An element"s atomic number is the number of protons in its nucleus. An element"s mass number is the sum of protons plus neutrons in the nucleus. Atomic mass, the atom"s total mass, can be approximated by the mass number. All atoms of an element have the same number of protons but may differ in number of neutrons. Isotopes are two atoms of an element that differ in number of neutrons. Radioactive isotopes decay spontaneously, giving off particles and energy. Some applications are radioactive isotopes in biological research are:

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