MODERN PERIODIC TABLE

Short History

•       In 1863, a 44 year old French geologist, A. E. Béguyer de Chancourtois created a list of the elements arranged by increasing atomic weight. The list was wrapped around a cylinder so that several sets of similar elements lined up, creating the first geometric representation of the periodic law.
•       In England, 32 year old analytical chemist John A. R. Newlands was also wrapping the elements, noting that chemical groups repeated every eight elements. He named this the octave rule, and compared it to a musical scale. Some less observant members of the English Chemical Society considered this absurd, so his work was ignored for years.
•        Chemists Dmitrii I. Mendeleev, a Russian, and German Lothar Meyer were working independently in 1868 and 1869 on the arrangement of elements into seven columns, corresponding to various chemical and physical properties. Their tables were similar - they acknowledged each other's work - the differences are subtle but important: Meyer's table was an accurate (for the time) accounting of the known facts about each element, such as melting point and atomic volume. The table clearly showed the existence of periodic chemical families. In 1870 Meyer's table and description of the periodic law was published in Liebig's Annalen.
•       A year earlier however, Mendeleev presented a much bolder and scientifically useful table.

Mendeleev's Statement of the Law of Periodicity

"The properties of the elements, as well as the forms and properties of their compounds, are in periodic dependence on, or (expressing ourselves algebraically) form a periodic function of, the atomic weights of the elements."

Modern Statement of the Law of Periodicity (Moseley)

"The properties of the elements, as well as the forms and properties of their compounds, are in periodic dependence on, or (expressing ourselves algebraically) form a periodic function of, the atomic number of the elements."

 Patterns in the Periodic Table: Main Features

•        There are 8 groups and 7 periods.
•        The columns are called groups.
•        The rows are called periods (hence periodic table).
•        Group 1 is called The Alkali Metals.
•       Group 2 is called The Alkaline Earth Metals.
•        The transition metals are in the middle. They have no group number.
•        The inner transition metals are at the bottom- lanthanides and actinides.
•        Group 7 is called The Halogens.
•        Group 8 is called The Noble Gases/ Inert Gases.

Hydrogen occupies a unique position at the top of the periodic table. It does not fit naturally into any Group.
All the members of a Group have the same valence configuration but different principal quantum numbers.
The number of valence electrons equals the Group number.
The period number equals the principal quantum number of the valence shell.

The periodic table is divided into BLOCKS.

1.      The s-block elements have valence configuration s¹ or s².

2.      The p-block elements have valence configuration s²p¹ to s²p⁶.

3.      The d-block elements have valence configurations in which d-subshells are being filled.

4.      The f-block elements have valence configurations in which f-subshells are being filled.