Chapter 2 - Chapter 2 The Chemistry of Life All matter is...

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Chapter 2 The Chemistry of Life All matter is composed of atoms What Are the Chemical Elements That Make Up Living Organisms? Atoms have volume and mass. Mass of one proton or one neutron = atomic mass unit (amu) or 1 dalton , or 1.7 × 10 –24 grams. Mass of one electron = 9 × 10 –28 —usually ignored Protons : positive charge +1 Electrons : negative charge –1 Neutrons : zero charge Atoms : # protons = # electrons—electrically neutral Element : pure substance containing only one kind of atom and are arranged in the periodic table . Atomic number: The number of protons identifies an element and is called the atomic number. Mass number = number of protons + number of neutrons. Mass number mass of atom in daltons. All elements except hydrogen have one or more neutrons. Isotopes : forms of an element with different numbers of neutrons, thus different mass numbers. Ex: 12 C has 6 neutrons, 13 C has 7 neutrons, 14 C has 8 neutrons Atomic weight : average of mass numbers of isotopes in their normally occurring proportions Radioisotopes are unstable, they give off energy in the form of alpha, beta, and gamma radiation from the nucleus. This radioactive decay transforms the atom, including changes in the number of protons. Radiation can damage cells and tissues. It is sometimes used to treat cancer
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The number of electrons determines how atoms will interact. Chemical reactions involve changes in the distribution of electrons between atoms.
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  • Spring '08
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