Name ____________________
Applied Chemistry
November 10, 2009
Periodic Table - Addendum
Periodicity
Trends or recurring variations in element properties with increasing atomic number.
Periodicity is caused by regular and predictable variations in element atomic structure.
Periodic Law
When the elements are arranged according to their atomic numbers, elements with
similar properties appear at regular intervals.
Representative Elements
Main-Group Elements
Groups on the left and right sides of the
periodic table.
Elements in groups 1, 2, and 13-18
Hydrogen
 Most common element in the universe
 One proton and one electron
 Can react with many other elements
Name ____________________
Trends Revisited:
Ionization Energy
 Ionization energy decreases as you move down a group/family.
o Group 1 elements have low ionization energies because the loss of an
electron forms a stable octet.
 Ionization energy increases as you move across a period.
o Decreasing atomic radius.
Atomic Radius
 Atomic radius increases as you move across the period.
o Electrons are added to the outer energy shell.
o Number of protons increases, the effective nuclear charge (+) increases
across the period.
 Atomic radius increases as you move down a group/family.
o Electrons found further from the nucleus due to additional energy levels
Electronegativity
 Electronegativity decreases as you move down a group/family.
o Increased distance between the valence electrons and the nucleus
o Atomic radius increases
 Electrongegativity increases as you move across a period.
o Each element gains one electron