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11 - Alkali metals Halogens Alkaline earth Proton and...

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Chem notes 8/29/11 Element is defined by number of protons; not electrons because they can move, if protons move than that’s a nuclear reaction Know element name of first six rows/periods Horizontal rows=periods Columns=groups Metal: solids at room temp except Hg, shiny, conduct heat and electricity, malleable, ductile, lose electrons to form cations in reactions, about 75% of all elements, found left of the periodic table, colorless (except Cu and Au) Nonmentals: exist in 3 states, poor conductors of heat and electricity, solids are brittle (no strong attractions holding them together), gain electrons in reactions to become anions, found to the right of the periodic table (except H) Metalloids: shiny, semiconducting, brittle Everything except transition metals and lanthanoids = main groups, representative elements Noble gases: neon and helium are the only gases to not form covalent bonds
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Unformatted text preview: Alkali metals Halogens Alkaline earth Proton and neutrons have almost the same mass; electrons have extremely small masses Atoms have a large amount of empty space Atomic number (Z): number of protons, defines element Mass Number (A): neutrons plus protons; isotopes have different number of neutrons Atomic symbol (X): ex. H, He, Na Isotopes are chemically identical; just different number of neutrons and therefore different masses. Radioisotope fall apart easily Knowing natural abundance allows us to calculate average mass Measuring mass is relative; to measure an objects mass is to compare it to a cylinder in France 1 amu = Carbon-12 mass/ 12 atomic masses on the periodic table are averages average atomic mass is calculated from the mass and abundance of each isotope...
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