Download Physical Science 100 Chapter 18, The Periodic Table

Physical Science 100
Chapter 18, The Periodic Table
The Periodic Law
The properties of elements are a periodic function of their atomic numbers (Moseley c.a. 1900)
The Periodic Table
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Horizontal rows of the periodic table are called periods or rows
Each period begins with an atom having one valance electron and ends with a complete outer shell
structure of an inert gas
Vertical columns of the periodic table are called groups or families
Elements in a group exhibit similar or related properties
The Roman numeral group number gives an indication of the number of electrons probably found
in the outer shell of the atom and therefore an indication of one of its possible valence numbers
Metals are found on the left of the chart with the most active metal in the lower left corner.
Nonmetals are found on the right ride with the most active nonmetal in the upper right-hand
corner.
Metals and non-metals are separated by a red “staircase”
Elements near this staircase are called semi-metals (or semi-conductors)
The noble or inert gases are on the far right.
Trends in the Periodic Table
Mendeleev created a table with elements arranged by atomic weights. He noted behaviors of chemical
properties that appeared to be periodic in weights.
Chemical Similarity in Families
• chemical behavior is dictated by the “valence” electrons
• the number of valence electrons is the same for elements in a family
• the “non-valence” electrons are “hidden” inside closed shells (according to the wave model) and
have little influence on chemical reactivity
Atomic Radius
• From left to right in the periodic table, atoms generally get smaller – the nuclear charge gets
bigger, pulling the electrons in closer.
• From top to bottom in the table, atoms generally get larger – the exclusion principle forces
electrons to occupy larger shells.
Ionization Energy – the energy required to take one electron from a neutral atom
• From left to right in the table, the ionization energy generally increases
• From top to bottom in the table, the ionization energy generally decreases
The Wave Model of the Atom
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electrons are described by standing waves of probability
electrons in the atom have discrete energies
electrons obey the Exclusion Principle
The grand accomplishment of science in the latter half of the
19th century was for Mendeleev and others to create the Periodic
Table.
It would be the grand accomplishment of Rutherford, Bohr, and
others in the opening decades of the 20th century to explain why
the mysterious periodic patterns exist.