5.4: periodicity

revisiting the periodic table

• Dmitri Mendeleev and Lothar Meyer independently came to the same conclusion about how elements should be grouped
• chemists mainly credit Mendeleev with the discovery primarily because he could predict elements that hadn’t been discovered yet and their properties (eg. germanium)
• periodicity: the repetition of properties at certain intervals

atomic numbers

• based on atomic masses → the basis of organization for the periodic table
• as atomic number increases, the size of the individual atom decreases

nuclear charge and ionization energy

effective nuclear charge

• many properties depend on attractions between valence electrons and the nucleus
• sizes of ions   * determined by interatomic distances in ionic compounds   * dependent on     * nuclear charge     * number of electrons     * the orbital in which electrons reside   * in an isoelectronic series, ions have the same number of electrons     * ionic radius decreases with increasing nuclear charge; positive ions have more protons than negative ions in an isoelectronic series

\ ionization energy (notation: I)

• ionization energy: the minimum amount of energy required to remove an electron from the ground state of a gaseous atom or ion   * the first ionization energy is the energy required to move the first electron; the second ionization energy is the energy required to move the second electron, etc., etc.   * the higher the ionization energy, the more difficult it is to remove electrons
• requires more energy to remove each successive electron
• metals vs. nonmetals   * metals tend to form cations (positively charged ions) whereas nonmetals tend to form anions (negatively charged ions)     * cations (+) are smaller than the parent atom     * anions (-) are larger than the parent atom

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