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