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 familiesValence electrons

• C. Nonmetals- Halogens- Noble gases

• B. Metals - Alkali metals

- Alkaline earth metals - Transition metals - Inner transition metals

- Representative elements

• D. Semimetals/metalloids

Compare properties of metals and nonmetals

III. Periodicity in properties • A. Ionization

energy

Ionization Potential/EnergyIE: Energy required to remove e-

Higher the IE: more difficult to remove e-

Across PeriodIE INCREASES* as the number of protons increases

* with decrease @ each subshellWhy? (effective nuclear charge)

Down GroupIE DECREASES as the number of shells

increasesWhy? (shielding, effective nuclear charge)

• B.Electronegativity

Electronegativity

The ability to attract e-

Across PeriodEN INCREASESBecause nuclear charge (# p+) increases

Down GroupEN DECREASESBecause more shells (n), more shielding, e- further away from nucleus

•C. Atomic/ionic radius

Atomic Radius

Across PeriodAtomic size DECREASES!Because nuclear charge (# p+) increases, as e- are added to same shell (n), pulls e- in tighter

Down GroupAtomic size INCREASESBecause more n (shells), more shielding,

e- further away from nucleus

Ionic

Ionic Radius

IonCharged atom

CationPositive (+) ion (neutral atom looses e-)

AnionNegative (-) ion (neutral atom gains e-)

IsoelectronicSame 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

Metallic CharacterIncreases

Nonmetallic 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