Chapter 8

1. Chapter 8 Relationships in the Periodic Table

2. A Brief Overview

3. A Series of Properties: Atomic Radius - one half the distance between the two nuclei in a covalent homonuclear molecules. Metals Diatomic Molecules Atomic Radius increases from top to bottom and decreases from left to right in the table.

4. Ionic Radius: • Corresponds to an ion • Cationic Radius - smaller than atomic due to decrease in repulsive and increase in attractive forces • Anionic Radius - larger than atomic due to increase in repulsive forces Loses 2 electrons Ca Ca+2

5. Ionization Energy The minimum energy required to remove an electron from a gaseous atom in its ground state. energy +X(g) ----> X+ (g) + e- energy + X+----> X+2(g) + e- second ionization energy + X+2 ----> X+3 (g) + e- third ionization I1 < I2 < I3 <… Increases from bottom to top and from left to right in the Periodic Table.

6. Electron Affinity: The energy exchange associated with an element when it accepts electrons in a molecular environment. Electronegativity: The tendency of an element in an isolated gaseous state to attract an electron toward itself. Electronegativity increases from bottom to top and left to right in the periodic table.

7. As you move from left to right in the periodic table you are putting electrons on the same shelf, so the shielding stays constant. At the same time you are increasing the positive charge in the center. This is the cause of many of the trends we have observed:

8. Summary of Facts and Concepts: • 1.Nineteenth century chemists developed the periodic table by arranging elements in the increasing order of their atomic masses. Discrepancies in early versions of the periodic table were resolved by arranging the elements in order of their atomic numbers. • 2.Electron configuration determines the properties of an element. The modern periodic table classifies the elements according to their atomic numbers, and thus also by their electron configurations. The configuration of the valence electrons directly affects the properties of the atoms of the representative elements.

9. 3. Periodic variation in the physical properties of the elements reflect differences in atomic structure. The metallic character of elements decreases across a period from metals through the metalloids and increases from top to bottom within a particular group of representative elements. • 4. Atomic radius varies periodically with the arrangement of the elements in the periodic table. It decreases from left to right and increases from top to bottom. • .Ionization energy is a measure of the tendency of an atom to resist the loss of an electron. The higher the ionization energy, the stronger the attraction between the nucleus and an electron. Electron affinity is a measure of the tendency of an atom to gain an electron.

10. The more positive the electron affinity, the greater the tendency for the atom to gain an electron. Metals usually have low ionization energies, and non-metals usually have high electron affinities. • 5. Noble gases are very stable because their outer ns and np subshells are completely filled. The metals among the representative elements (in Groups 1A,2A, and 3A) tend to lose electrons until their cations become isoelectronic with the noble gases that precede them in the periodic table. The nonmetals in Groups 5A,6A, and 7A tend to accept electrons until their anions become isoelectronic with the noble gases that follow them in the periodic table.

11. Key Words: Amphoteric Oxide Atomic Radius Diagonal Relationship Electron Affinity Ionic Radius Ionization Energy Isoelectronic Noble Gases Representative Elements Valence Electrons

12. The End