Periodic Table and Periodicity

Dmitri Mendeleev “The elements, if arranged according to their atomic weights, exhibit an apparent periodicity of properties.”

I. History A. Dimitri Mendeleev, 1869 B. Moseley, 1914 periodic law: The chemical and physical properties of the elements are periodic functions of their atomic numbers; When the elements are arranged in order of increasing atomic number, there is a periodic repetition of their properties.

II. Structure/Organization A. Periodic table Periods Groups or families Valence electrons - Representative elements B. Metals - Alkali metals - Alkaline earth metals - Transition metals - Inner transition metals C. Nonmetals - Halogens - Noble gases D. Semimetals/metalloids

Compare properties of metals and nonmetals

Periodicity in properties A. Ionization energy

Ionization Potential/Energy IE: Energy required to remove e- Higher the IE: more difficult to remove e- Across Period IE INCREASES* as the number of protons increases * with decrease @ each subshell Why? (effective nuclear charge) Down Group IE DECREASES as the number of shells increases Why? (shielding, effective nuclear charge)

B. Electronegativity

Electronegativity The ability to attract e- Across Period EN INCREASES Because nuclear charge (# p+) increases Down Group EN DECREASES Because more shells (n), more shielding, e- further away from nucleus

C. Atomic/ionic radius

Atomic Radius Across Period Atomic size DECREASES! Because nuclear charge (# p+) increases, as e- are added to same shell (n), pulls e- in tighter Down Group Atomic size INCREASES Because more n (shells), more shielding, e- further away from nucleus

Ionic

Ionic Radius Ion Charged atom Cation Positive (+) ion (neutral atom looses e-) Anion Negative (-) ion (neutral atom gains e-) Isoelectronic Same electron structure

Ionic Radius Across Period IR DECREASES* (why?) * with jump up in size @ metalloids! Down Group IR INCREASES Compare to neutral atom Valence e- are the outermost e- of an atom

D. Metallic character/nonmetallic character Nonmetallic character increases Metallic Character Increases

Metallic Properties Across Period Metallic Properties DECREASES Down Group Metallic Properties INCREASES

Summary of Periodic Table Trends Moving Left --> Right Atomic Radius Decreases Ionization Energy Increases Electronegativity Increases Metallic character decreases Moving Top --> Bottom Atomic Radius Increases Ionization Energy Decreases Electronegativity Decreases Metallic character increases