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The periodic table of elements is a graph (a table) in which all the chemical elements known to man are arranged, ordered according to their atomic number (protons), electron configuration and specific chemical properties.
It is a fundamental conceptual tool for the study of matter whose first version was published in 1869 by Russian chemist Dmitri Mendeleev, and which has been updated over the years as new chemical elements have been discovered and the patterns underlying their properties have been better understood.
The current periodic table is structured in seven rows (horizontal) called periods and in 18 (vertical) columns called groups or families. Chemical elements are arranged according to their properties from left to right and top to bottom, in decreasing order of their atomic numbers.
See also: Examples of chemical elements from the periodic table
Groups of the periodic table
Numbered 1 through 18 from left to right, current group names are determined by nomenclature IUPAC approved in 1988 to unify the diverse forms of name that existed. The elements of each group have similar electronic configurations and the same valence (electrons in the last orbit), so they have similar chemical properties.
There are the following groups of elements, according to IUPAC:
- Group 1 (IA). All alkali metals, with the exception of hydrogen, which although nominally in the group, is a gas. The elements are part of the family: lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr). They have very low densities, are good transmitters of heat and electricity, and they are never found freely in nature, but rather in compounds with other elements.
- Group 2 (IIA). The so-called alkaline earth metals are harder than the alkaline ones, bright and good electrical conductors, although less reactive and very good reducing agents (oxidants). The family consists of: beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba) and radium (Ra).
- Group 3 (IIIB). They constitute the scandium family, although in many of the groups in segment “d” of the table (groups 3 to 12, including actinium and rare earths) there is no definitive consensus regarding the ideal arrangement. This family is made up of scandium (Sc), yttrium (Y), lanthanum or lutetium (La) and actinium (Ac), they are solid, shiny and highly reactive, similar in properties to aluminum.
The so-called “rare earths” or internal transition elements also belong to this group: lanthanides (or lanthanides) and actinides (or actinoids), which are found in a lower block of the table. Lanthanides are: Lanthanum (La), Cerium (Ce), Praseodymium (Pr), Neodymium (Nd), Promethium (Pm), Samarium (Sm), Europium (Eu), Gadolinium (Gd), Terbium (Tb), Dysprosium (Dy), Holmium (Ho), Erbium (Er), Thulium (Tm), Ytterbium (Yb), Lutetium (Lu). Actinides are: thorium (Th), proactinium (Pa), uranium (U), neptunium (Np), plutonium (Pu), americium (Am), curium (Cm), berkelium (Bk), californium (Cf), einsteinium (Es), fermium (Fm), mendelevium (Md), nobelium (No) and lawrencio (Lr). From neptunium onwards they are unstable isotopes created by man.
- Group 4 (IVB). The so-called titanium family is made up of the elements titanium (Ti), Zirconium (Zr), Hafnium (Hf) and Rutherfordium (Rf), the latter synthetic and radioactive, so it is sometimes not taken into account. They are highly reactive metals, so in certain presentations they can instantly become red and inflamed just by coming into contact with the oxygen in the air.
- Group 5 (VB). The vanadium (V) family, logically headed by this element and accompanied by niobium (Nb), tantalum (Ta) and dubnium (Db), the latter exclusively produced in laboratories. They are solid at room temperature, silver in color, and conduct heat and electricity.
- Group 6 (VIB). The chromium (Cr) family, made up of molybdenum (Mo), tungsten (W) and seaborgium (Sg), are solids with a high melting and boiling point, conductors of heat and electricity, very resistant to corrosion and quite reagents.
- Group 7 (VIIB). In this family are manganese (Mn), technetium (Tc) and rhenium (Re), as well as the element with atomic number 107, bohrium (Bh). The latter was synthesized for the first time in 1981, it is highly unstable so its half-life is just 0.44 seconds. In general, rhenium and technetium are also extremely rare elements, the latter lacking in stable forms, while manganese is very frequent in nature.
- Group 8 (VIIIB). The Iron (Fe) family includes Ruthenium (Ru), Osmium (Os) and Hassium (Hs). The latter was known as Unniloctio and was synthesized in 1984 for the first time; it is listed among controversial items 104 to 108, whose nomenclature has been questioned. They are quite reactive elements, good conductors of heat and electricity and, in the case of iron, magnetic.
- Group 9 (VIIIB). This family is that of cobalt (Co), rhodium (Rh), iridium (Ir) and meitnerium (Mt). As in the previous group, the former is ferromagnetic and representative of the properties of the family, and the latter is synthetic, so it does not exist in nature. Its most stable isotope, in fact, lasts about 10 years.
- Group 10 (VIIIB). Together with groups 8 and 9, this family constituted in previous versions of the Periodic Table a single group of elements. Recent versions have separated them, and this one is led by nickel (Ni), which is accompanied by Palladium (Pd), Platinum (Pt) and Darmstadtium (Ds). They are common metals in nature in elemental form, although nickel, being the most reactive, can be found in alloy (in some meteorites, especially). Their catalytic properties make these metals an important supply for the aerospace industry.
- Group 11 (IB). The so-called copper (Cu) family is made up of the precious metals gold (Au) and silver (Pb). They are also known as "coin metals". They are quite unreactive, difficult to corrode, soft and extremely useful to man.
- Group 12 (IIB). This group contains the so-called Zinc (Zn) family, such as cadmium (Cd), mercury (Hg) and copernicium (Cn), formerly called ununbium. They are soft metals (in fact, mercury is the only liquid metal at room temperature), diamagnetic and divalent, with the lowest melting points of all transition metals. The funny thing is that zinc is very necessary for the chemistry of life, while cadmium and mercury are highly intoxicating. Copernicium, for its part, is a synthetic element created in 1996.
- Group 13 (IIIA). These elements are known as earthy elements, since they are abundant in the earth, especially aluminum. The group is headed by boron (Br), which is a metalloid, and then aluminum (Al), gallium (Ga), indium (In) and thallium (Ta), increasingly metallic as one descends in the column . And although borium has high hardness and non-metallic properties, the others are soft and malleable metals widely used by man.
- Group 14 (VAT). The carbonid elements, logically headed by carbon (C), silicon (Si), germanium (Ge), tin (Sn) and lead (Pb), all well-known and widespread elements, especially the first, indispensable for all the chemistry of life. As one moves down the family, however, the elements acquire metallic properties, to the point that carbon is non-metallic, silicon and germanium are semi-metallic, and the last two are clearly metallic.
- Group 15 (VA). It is the group of nitrogenoidal elements, headed as their name indicates by nitrogen (N), then phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi) and muscovio (Mc), a synthetic element. They are also known as pannogens or nitrogenoids, they are very reactive at high temperatures and many are indispensable for organic chemistry.
- Group 16 (VIA). Called chalcogens or ampigens, they are in the oxygen (O) family, followed by sulfur (S), selenium (Se), tellurium (Te) and polonium (Po). They are characterized by having six valence electrons, despite which their properties vary from non-metallic to metallic as their atomic number increases. At room temperature, oxygen is a gas, highly reactive due to its small size, while the rest are solid and less frequent in nature.
- Group 17 (VIIA). The family of halogens, a name that comes from its tendency to form salts (halides). This is due to the fact that they generally constitute diatomic molecules of considerable oxidizing power, which leads them to form mononegative ions. Therefore, they are widely used in the chemical industry and in the manufacture of laboratory supplies. These elements are fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astate (At) and tenese (Ts), the latter being also a metal of group f.
- Group 18 (VIIIA). Known as noble gases or inert gases, they are elements of very low reactivity, which are usually found as monatomic gases, odorless, colorless, tasteless, forming very few and exceptional compounds, due to their complete electron shell. These elements are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), radon (Rn), and oganeson (Og). These last two are particular: radon is radioactive and has no stable isotopes, so it survives for just 3.8 days; while oganeson is of synthetic origin and the heaviest element created to date.
Periodic Table Blocks
Another way to understand the periodic table is through its blocks, which are four:
- Block s. It comprises the first two groups, that is, alkali and alkaline earth metals, in addition to hydrogen and helium.
- Block p. It includes the last six groups, that is, from 13 to 18 in the periodic table and also all the metalloids.
- Block d. It includes groups 3 to 12 and all transition metals.
- Block f. Includes rare earths: lactanides and actinides. It does not have its own group numbers, although it is assumed that these elements would belong to 3.
- Block g. A hypothetical block, in which the elements that can be synthesized in the future would go.
