Knowledge database: Basics: Periodic table of elements

The periodic table of elements, as we know it today, was designed by a Russian chemist named Dmitri Ivanovich Mendeleev. The periodic table of elements (PTE), is a special arrangement of elements in which elements are grouped in precise rows and columns because of exact reasons. Each row of elements is broken when a new element, that has properties similar to the first element in the row that is broken, appears. This phenomenon was the guiding principle for the creation of the first form of PTE, although today we know that the very structure of the atom and the electron cloud also show periodicity, and thus further confirm the PTE.

Regarding columns, the PTE is divided into following groups:

Group 1: lithium, sodium, potassium, rubidium, cesium, francium
Group 2: beryllium, magnesium, calcium, strontium, barium, radium
Groups 3-12: Transition metals, i.e. elements
Group 13: boron, aluminum, gallium, indium, thallium
Group 14: carbon, silicon, germanium, tin, lead
Group 15: nitrogen, phosphorus, arsenic, antimony, bismuth
Group 16: oxygen, sulfur, selenium, tellurium, polonium
Group 17: fluorine, chlorine, bromine, iodine, astatine
Group 18: helium, neon, argon, krypton, xenon, radon

+ Hydrogen, which could, by its properties, be classified into both the group of alkali and the group of halogen elements. Because of that, hydrogen is often placed separately in the PTE.

Each element in the PTE, is marked by its symbol and atomic (or proton) number. The relative atomic mass of the element is also mentioned. In addition, sometimes additional information is also available, most commonly the oxidation states. More about this data will be provided in other chapters.

Also, in the descriptions of individual properties, the ways some properties increase or decrease throughout the PTE will also be mentioned.