The periodic table is a model that groups together all known chemical elements and their properties . The elements are organized in increasing order according to their atomic numbers.
The most recent periodic table has 118 elements, 92 natural and 26 artificial .
Each square specifies the name of the element, its symbol and its atomic number.
Organization of the periodic table
The elements are arranged in increasing order according to their atomic number . The atomic number (number of protons) is located above the symbol of the element. Beneath the symbol of the element is the atomic mass or atomic weight (the sum of protons and neutrons).
The periodic table is composed of horizontal lines called periods and vertical columns called groups or families .
The periods are numbered from 1 to 7, from top to bottom, on the left side of the table, and groups are listed from 1 to 18, from left to right, at the top of the table. Previously the groups were denominated with Roman numbers (from I to VIII) and in two groups: A and B.
The members of a period have the same number of electronic layers, totaling seven periods. However, they do not necessarily have the same characteristics. For example, sodium (Na) and magnesium (Mg) tend to lose electrons, but sodium loses one while magnesium loses two electrons. Chlorine (Cl), which also belongs to period 3, tends to gain an electron.
The members of a family have the same number of electrons in their outermost layer, that is, the valence shell . In addition, they have similar chemical properties. Thus, all elements of family 1 (or AI), which groups the elements lithium, sodium, potassium, rubidium, cesium and francium, tend to lose an electron in the reactions.
- Family 1 (IA): alkali metals. In the reactions, these elements lose an electron. In this family are sodium and potassium, important elements for life.
- Family 2 (IIA): alkaline earth metals . In the reactions, these elements lose two electrons. In this family calcium is found, important for the formation of bones and teeth.
- Family 17 (VIIA): halogens . These elements tend to gain an electron when they react. The outstanding members in this group are chlorine, a component of kitchen salt and lye, and iodine used in disinfectants.
- Family 18 (VIIIA): noble gases . These elements have their last full valence layer, so they are very stable.
The elements in families 3 through 12 are called elements or transition metals .
The two periods in the lower part of the periodic table represent two special groups. The period that starts with Lantano (57) is called of the lanthanidesand the period that starts with actinium (89) is called the actinides . These elements are sometimes called as rare earths, because initially it was difficult to separate them and identify them.
History of the periodic table
In 1786, the French chemist Lavoisier tried to organize the 30 known elements, classifying them as metallic, non-metallic, gas and earth elements according to their properties.
In 1829, the German chemist Döbereiner found that certain groups of three elements (triads) possessed similar properties.
Julius Lothar Meyer (German chemist, 1830-1895) and Dimitri Mendeleyev(Russian chemist, 1834-1907) each developed their own versions of the periodic table. Both recognized a repetitive pattern in the chemical elements known until the first half of the 19th century.
Meyer published his table of 28 elements for the first time in 1864, based on the atomic mass and chemical properties of the elements. Mendeleyev arranged the elements according to the atomic mass and left blank spaces, predicting the existence of elements that had not yet been discovered. This earned him recognition as the father of the periodic table.
In 1913, Henry Moseley (1887-1915) established the concept of atomic number as the key aspect in the organization in the modern periodic table. The atomic number is the number of protons in the nucleus.
In 1945, Glenn Seaborg (1912-1997) suggested that elements from actinium (number 89) should be considered in rare earths. Seaborg also contributed to the creation of the lanthanide and actinide series, which are the periods represented below the periodic table.
The updated periodic table dates from November 28, 2016 and includes the elements 113 (Tennessine), 115 (Nihonium), 117 (Moscovium) and 118 (Oganesson).
UNESCO established 2019 as the “international year of the periodic table” to celebrate 150 years of recognition of Mendeleyev’s periodic system.
Discovery of noble gases
For a long time the noble gases (helium, neon, argon, krypton, xenon and radon) were known as inert gases, because they were thought not to react at all. In 1962, Neil Bartlett discovered that under special conditions these gases can form compounds with other elements. Since then, it is called noble gases.
Most abundant elements
The first two elements of the periodic table, hydrogen and helium, represent 90% of the matter in the entire universe.
Organization in charge of the periodic table
The IUPAC (for the abbreviations in English International Union of Pure and Applied Chemistry) is the organism in charge of the update of the periodic table and to establish the criteria for the creation and designation of new elements.
Names of elements
One of the disadvantages that the IUPAC had when choosing the name of an element was its insistence that the element was not named in honor of a person still alive. In 1993, the Americans called the element 106 seaborgio, by the scientist Glenn Seaborg (1912-1997), who at the time was alive.
Creation of new elements
Thanks to advanced technological developments, the creation of new elements has been achieved. The initiator of this field was Glenn Seaborg, who first synthesized plutonium in 1943 and was responsible after the synthesis of many of the transuranic elements.