The Periodic Table Of Chemistry is an arrangement of the chemical elements in the form of a table, ordered by their atomic number (number of protons), by their configuration of electrons and their chemical properties.

The atomic weights.

Atomic weight (also called Relative Atomic Mass), was developed by John Dalton in the nineteenth century, his contribution consisted in the formulation of a chemical atomism that integrated element and weight laws. This scientist, took substances of his time and assumed how the atoms of these were combined, I take as reference the mass of a hydrogen atom and from experiences and assumptions built the first table of relative atomic masses. Periodic Table Of Chemistry was perfected with the congress of karlsruhe in 1860. Dalton employed the knowledge of proportions in which the substances of his time reacted and made some assumptions about the way in which the atoms of the same were combined.

Metals, non-metals and metalloids or transition metals.

The first classification of known elements was proposed by Antoine Lavoisier, who proposed that the elements be classified into metals, non-metals and metalloids or transition metals. Although very practical and still functional in the modern periodic table, it was rejected because there were many differences in both physical and chemical properties.

It is called metals to the chemical elements characterized by being good conductors of heat and electricity. They have high density and are solid at normal temperatures, except for mercury.

It is called not metals, the chemical elements opposed to metals because their characteristics are totally different. Its surface is opaque, and are poor conductors of heat and electricity. Compared to metals, they are low density, and melt at low temperatures.

Elements that can not be classified as metals or non-metals; Have properties of the two groups and are called metalloids or semi-metals. They are solid at room temperature and form positive ions with difficulty. Depending on the circumstances they have one or the other behavior.

Importance of periodic table.

The relevance of Periodic Table Of Chemistry lies in the fact of presenting the known elements in a way that is easily understood. This order can be very useful from the pedagogical point of view in that it offers much information regarding the basic constituents of the subject. It was developed over time as scientific knowledge was advanced; It is for this circumstance that in its history can come to present many modifications and corrections. Nowadays, it is a fundamental element for anyone who is graduating in the hard sciences.