The Periodic Table of Elements

Currently, more than 100 elements are known. Most of them occur naturally, while others are made artificially.

These elements vary greatly in their physical and chemical properties as well as in the characteristics of their compounds. It has long been recognized that if the elements could be classified, it would simplify their study.

Dmitri Mendeleev, a Russian chemist in the middle 19th century, was first given credit for arranging the elements in a usable manner. He observed that when the elements were arranged in order of increasing atomic mass, similiar chemical and physical properties appeared at regular, or periodic, intervals.

While this was close, some irregularities did exist. The current table is arranged according to atomic number (# of protons), thanks to the work of English scientist Henry Moseley.

Table Information is provided below...

Trends of the Table:

Families contain similiar chemical properties
Atomic Radius increases as you move down a column and from right to left across a period
Ionization Energy increases up a column and from left to right across a period
Electronegativity increases the same as ionization energy

Atomic Number = # of protons
Atomic Mass = protons + neutrons
Oxidation states = # of electrons lost/gained in a reaction
2-4 = # of electrons and location in shells
In a neutral atom: # protons = # electrons
Isotope: an atom with a different # of neutrons than an atom of the same element
Ion: loss or gain of electrons from a neutral atom