http://www.ck12.org Chapter 6. The Periodic Table
FIGURE 6.20
Summary of periodic trends within peri-
ods and groups.Lesson Summary
- The chemical behavior of elements can largely be explained by electron configurations.
- The elements on the far left of the periodic table (groups 1 and 2) are very reactive as pure metals, while the
noble gases (group 18) are almost totally unreactive. - Ionization energy is the energy required to remove an electron from a specific atom. Ionization energy
generally increases as you move left to right across the table or from bottom to top. - Electron affinity is the energy required for an electron to be added to a neutral atom in its gaseous form.
Because most atoms release energy when an electron is added, most electron affinity values are negative.
These values generally become more negative (more energy is released) as you move left to right across the
table or from bottom to top. - Ionic radius helps to indicate the size of an ion as compared to its parent atom. Cations always have a smaller
atomic radius than the parent atom; anions always have a larger atomic radius than the parent atom. - When an atom gains an electron, its radius increases. Conversely, when an atom loses an electron, its radius
decreases. The radius of an anion is larger than the radius of a neutral isoelectronic atom because there are
fewer protons available to attract the same number of electrons. The reverse is true for cations. - Electronegativity is a measure of the relative tendency of an atom to attract electrons to itself when chemically
combined with another atom. In general, electronegativity increases as you move left to right across the table
and from bottom to top. - Periodic trends in metallic and nonmetallic characteristics mirror those of the other properties that we have
discussed; the most metallic elements are at the lower left of the table, and the most nonmetallic elements are
at the upper right.
Lesson Review Questions
- Compare and contrast the characteristics of metals and nonmetals.
- Write the electron configurations for the following ions:
a. Li+
b. Be^2 +
c. N^3 −
d. O^2 −