Small Molecules and the Chemistry of Life.docx

Small Molecules and the Chemistry of Life.docx - Ch 2 Small...

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Ch. 2 Small Molecules and the Chemistry of Life Six elements ( C, H , O, N, P and S ) make up most of the matter in living organisms Reactive atoms tend to gain or lose electrons from their valence (outer) shell in order to achieve a fully valence shell which confers stability Atoms are composed of: Electrons- negligible mass, negative charge In the atomic nucleus: Protons- have mass. positive charge Neutrons – have mass: no charge Generally, atoms are electrically neutral: # of electrons = # of protons Important definitions: Atoms: the smallest part of an element (electrons, protons, neutrons) Element: pure chemical substance containing only one kind of an atom Atomic number: number of protons -Number of protons or electrons determines how an element behaves in chemical reactions -Mass number= protons + neutrons Molecule: 2 or more atoms chemically joined together (H20, 02 etc) Compound: A molecule made up of 2 0r more elements bonded together in a fixed ratio Molecular weight: of a compound = sum of atomic weights of all atoms in the molecule Orbital: Region where an electron is found at least 90% of the time Octet rule: tendency of atoms to form stable molecules resulting in full valence/ outermost shells Chemical Bond: Attractive force that links atoms together to form molecules Covalent bonds: atoms share one or more pairs of electrons so that the outer shells are filled
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