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Chemistry Essentials - o Electron cloud model(ECM shows...

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Chemistry Essentials Chemistry is the basis for biology Basic structural concepts Atom: smallest part of a pure substance, or element, that still has the properties of that substance Molecule: a particle made up of one or more atoms bound together Element: a pure substance, made entirely of one kind of atom (all known elements are listed in the Periodic Table) Compound: substance made of molecules that contain more than one kind of atom Atomic structure and function Many different models exist; none are perfect o We'll look at the Bohr model and electron cloud model first —then later structural and space-filling models o Bohr model (named for Niels Bohr) shows electrons orbiting the nucleus like planets orbit the sun
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Unformatted text preview: o Electron cloud model (ECM) shows electrons as a cloud surrounding the nucleus • Nucleus o Protons have positive (+) charge; number of protons is "atomic number" and signifies kind of atom (which element) o Neutrons have no charge; optional and variable in number (isotopes) • Electrons o Electrons have a negative (-) charge and do not affect the type of element o Electrons may be present in regions called energy levels The further from the nucleus, the more energy is needed by the electron to stay there --so the higher energy levels are farther from the nucleus The lowest (first) energy level can contain up to two electrons The next few can hold up to eight electrons each (the "octet rule")...
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