Chapter 18: The Periodic Table

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This chapter is a preview for the next few chapters. As such it raises some questions that will be addressed later in coming chapters. The Periodic Table (or Chart) is an attempt to organize our knowledge of the chemical elements. You do not have to memorize all of the chemical symbols or names of the elements for this class. (These are always provided with the examinations.) Rather, you should try to learn the patterns of chemical behavior that the table summarizes. It was a grand accomplishment of physics in the 20th century to understand why the patterns were there in terms of the wave model of the atom. Definition: "Ionization energy" is the energy required to (add, remove?) an electron (to, from?) an atom. Pattern: The ionization energy of helium is (smaller, larger?) than the ionization energy of lithium. The ionization energies of the elements show a periodic behavior that systematically changes along a (column, row?) of the Periodic Table. Pattern: Metals are found to the (right, left?) of the Table and nonmetals are found to the upper (right, left?) of the Table. Pattern: Atoms tend to get (larger, smaller?) as you move downward in a column. Pattern: Atoms tend to get (larger, smaller?) as you move from left to right in a row. The Wave Model of the Atom (with its associated energy levels, orbitals and shells) explains patterns in the Periodic Table. Rule: In Shell 1, only the -orbital is possible. In Shell 2, the s- and -orbitals are possible. In Shell 3, -, p-, and -orbitals are possible. Etc. Rule: The Exclusion Principle says that you may only have (how many?) electrons in an s-orbital in a particular shell, (how many?) electrons in p-orbitals in a particular shell and (how many?) electrons in d-orbitals in a particular shell. Because of the Exclusion Principle, shells within atoms fill up, forcing additional electrons into new (higher energy) shells. When a shell fills or the s+p orbitals fill, a new (row, column?) is formed in the Periodic Table. Can you look at the Table and see where s-orbitals are being filled, where p-orbitals are being filled, and where d-orbitals are being filled? (Look for blocks of 2, 6 and 10 atoms.) Electrons in unfilled shells are called electrons. Pattern: In the Periodic Table, elements with the same number of valence electrons are found in the same (row, column?) . Elements with the same number of valence electrons have (similar, dissimilar?) chemical behavior. Pattern: Columns of the Periodic Table are labelled (in Roman Numerals) to indicate the number of valence electrons for the elements in that column. Lithium (Li), sodium (Na), potassium (K) in Columns IA are called "alkali metals." The have (how many?) valence electron(s). Boron (B) and aluminum (Al) in Column IIIA have (how many?) valence electron(s). Helium (He), neon (Ne), argonne (Ar), etc. in Column VIIIA are called "noble gases." They have full shells; they have no valence electrons. Elements in the same (row, column?) are said to belong to the same "family" or "group." Elements in the same (row, column?) are said to belong to the same "period." Elements in the same period exhibit systematic changes in chemical behavior that is best illustrated in the changes in the of the compounds the elements of the period form.

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