Periodic Trends Chemistry I

What patterns can you find on the Periodic Table? We have already discovered that The Periodic Table is organized in order of increasing atomic number. Elements in groups have similar physical and chemical properties.

Here are some important patterns (aka trends): Atomic radius Electronegativity Ionization energy

Atomic Radius distance from the center of an atom's nucleus to its outer most electron Measured in picometers (10-12)

Electronegativity The ability of an atom in a molecule to attract shared electrons to itself. The Pauling scale measures elements from a scale of .7 to 4.0

Ionization Energy The amount of energy required to pull the outer shell electron from an atom. Example: Na + energy --> Na+ + e-

What causes these patterns? Shielding Core charge

Shielding The shielding of the outer shell electrons from its attraction to the nucleus The inner levels of electrons do the shielding

Effective nuclear charge The strength of the nucleus’ positive attraction for electrons Core charge = proton charge + core electron charge (core electrons are everything except for the valence electrons)