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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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