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Atomic Number and Mass

Atomic Number and Mass. Atomic Number. Mass. In the periodic table Equal to the number of protons Defines an element’s physical and chemical properties Also equal to the number of electrons (in a neutral atom). Mass Number: Not on the periodic table

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Atomic Number and Mass

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  1. Atomic Number and Mass

  2. Atomic Number Mass • In the periodic table • Equal to the number of protons • Defines an element’s physical and chemical properties • Also equal to the number of electrons (in a neutral atom) • Mass Number: • Not on the periodic table • Equal to the number of protons plus the number of neutrons (totals the number of particles in the nucleus) • Atomic Mass: • On the periodic table • Is a weighted average of the mass numbers of various isotopes • Isotopes = atoms of the same element, having different numbers of neutrons

  3. Isotope Notation: Isotope name vs. symbol? Number of protons, electrons, neutrons? Carbon – 12 Carbon – 14

  4. Calculating Average Atomic Mass: Boron has two naturally occurring isotopes. Boron – 10 has an abundance of 19.8 %. Boron – 11 has an abundance of 80.2 %. Average atomic mass of Boron? Atomic mass unit (amu)

  5. History continued… • 1790s • Lavoisier composed a list of 23 known elements • Mid-1800s • About 70 elements are known • Mendeleev organizes the Periodic Table by atomic mass • 1913 • Moseley re-organizes the Periodic Table by atomic number • Periods  • Groups (families) 

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