Also called Mendeleev’s table, the periodic table is an organized grid comprising Earth’s chemical elements. There are 118 elements (as of July 2016) on the table, which are purposely positioned to depict their chemical property differences and similarities with other elements. Out of the 118 elements, 94 are natural and the remaining 24 produced synthetically. Metals and non-metals are separated from each other, with non-metals taking up the right and metals occupying the left portion of the table.
Structure and Arrangement
Periodic table elements are organized based on increasing atomic numbers and similarity. The positioning helps predict the properties of the element, such as number of atoms an element has (courtesy its atomic mass) or its electron configuration. Elements with more or less identical properties are placed in proximity to each other on the table as columns, called groups (formerly known as families).
Every column on the table is a group. The periodic table has 18 groups. A group comprises elements having the same electron count in their outermost or valence shell. For example, the first group or column has elements that have a single electron in their outermost shells. Similarly, the second column has elements that have two electrons in their valence shells.
The seven horizontal rows are called periods, with a couple of smaller periods below them. These periods comprise elements with similar properties. For instance, the two row blocks house actinides and lanthanoids. These groups of elements are called inner transitional metals.
Symbols and Box Information
The table doesn’t have the full names of the elements mentioned, due to space limitations. Knowing what these symbols stand for is imperative to find out which element it signifies. Generally, the symbol or short form is derived from the actual element name. However, there are instances when the symbols and actual element name have little to no connection. For example, Hg is the symbol for the element ‘mercury.’
Besides having the element symbol, each grid on the table also gives out additional information about the element, which makes it easier to find an element’s atomic mass, atomic number, valence numbers and electron configuration.
Before 1700, there were only 12 elements. With time, more elements were discovered. Johann Dobereiner, a German scientist, first tried organizing elements based on their physical and chemical properties. In 1817, Dobereiner saw specific chemically similar elements could be pooled with each other in threes based on their atomic weight patterns – for instance, calcium, strontium and barium; lithium, sodium and potassium. As a result, in 1829, Dobereiner came up with the Law of Triads. Thereafter, other scientists attempted finding more patterns between larger element groups.
In 1862, Alexandre-Émile Beguyer de Chancourtois, a French geologist, came up with another arrangement as per which the elements were organized by ascending atomic weights and vertically lining up similar elements. In 1863, John Newlands, an English chemist, attempted a similar classification based on atomic weight. He too witnessed a pattern between elements, which he named Law of Octaves.
During the late 1800s, a Russian scientist named Dmitri Mendeleev, who is known as the father of the modern periodic table, arranged the elements by increasing atomic weights. Unlike his counterparts, Mendeleev chose to move specific elements to new spots on the table based on their atomic weights, to group elements with similar properties.
His periodic table was published in 1869, and has been in use ever since. As not all elements were discovered (only 60 of them were known) at that time, the periodic table had some empty space for elements that weren’t discovered yet. For instance, noble gases, a fresh element group, was discovered during the 1895-1901 period.