The periodic table is a table representing all the chemical elements, ordered by increasing atomic number and organized according to their electronic configuration. The electronic configuration of elements underlies their chemical properties. It is also called the periodic table of the elements or the Mendeleev table,
History of Periodic Table
It was developed by the Russian chemist Dmitri Mendeleev in 1869. Since then it has undergone many readjustments to arrive at the form which is used today. In its current form, the periodic table has 7 periods and 18 columns.
The idea of classifying the elements in a table began with the German chemist Johann Wolfgang Dobereiner in the early 19th century. he was the first to imagine a grouping of chemical elements together. According to him, some elements have chemical properties that can be comparable, which leads him to try to combine them in a triad.
In the middle of the XIXth century, appears the geologist Alexandre-Emile Beguyer de Chancourtois, he classifies for the first time the elements according to their atomic mass. Unfortunately, he used unusual terms, which means that his discovery remains little publicized.
After Alexandre-Emile, John Alexander Reina Newlands was the first to publish a periodic table of the elements and completed it with his hypothesis of the law of octaves: the chemical properties of each element is repeated every 8 times. But it is really another scientist who will revolutionize the classification of elements, it is Dmitri Ivanovich Mendeleev.
Importance of the periodic table
Since its development, the periodic table continues to be a relevant instrument in the comparison between chemical elements. It makes it possible to rationally study the great variety of substances present in nature. It also helps to unify knowledge about these substances and facilitates the understanding of the groups to which they belong, by determining the relationship between their chemical properties and their atomic structure. It is also important in predicting the formulas of compounds as well as the types of bonds that can unite them in a molecule.
The periodic table provides a number of information about materials such as atomic mass, atomic radius, electron configuration, among others.
2 forms of periodic tables:
Dmitry Mendeleev’s periodic table
The table proposed by Dimitri Ivanovich Mendeleïev classified by increasing atomic mass (M) the 63 elements known until then. It was also characteristic by the inversion of some elements, so as to place in columns the elements with similar chemical properties, for example, Iodine I and Tellurium Te. In Mendeleev’s painting some boxes were left empty to be filled with elements still unknown.
Periodic Classification of the Elements in its present form
In the current classification, there are 7 periods, each of which is associated with a quantum number n: the n-th line begins with the filling of the ns orbital and ends when the np sub-layer is filled. There are also 18 columns, each of which groups together the elements of the same electronic valence configuration.
Structure of the periodic table
The periodic table is structured into three regions: metals, nonmetals, and metalloids. In this structure, the elements belonging to the same region share common physical and chemical properties.
Metals constitute the majority of elements of the periodic table. They occupy the left part of the line going from boron (B) to astatine (At). With the exception of mercury (Hg), all metals are solid at room temperature. Most metals react with acids and are ductile, malleable and shiny. They are also good conductors of electricity.
Non-metals are positioned on the right - hand side of the periodic table. They are very varied properties and different from those of metals. They are lusterless, bad conductors of electricity and heat. They are not ductile.
Metalloids are elements that are similar to metals. The denomination metalloids mean “similar to metals”. They locate all along the border of the painting, shaped like a staircase, and separate metals from non-metals. They share certain properties of metals such as the conduction of electricity.
In addition to the three regions, there are also periods and families. The periods are formed by the horizontal rows in which the electrons of the elements are distributed over the same number of electronic layers, a number given by the period number. As the atomic number increases in the period, the radius of the atom and the metallic properties decrease.
Families are on their side, formed by the vertical columns. The elements of the same family have similar properties, which is justified by their electronic configuration. In addition, the elements of the same family have the same number of valence electrons, which corresponds to the number of the family.
As the atomic number increases in the family, the radius of the atom also increases and the ionization energy decreases. There are four main families: alkalis, alkaline earths, inert gases and halogens.
Alkalis are soft, light, silvery-looking metals. They do not exist in their pure state in nature; they are always combined with other elements. They are also characterized by their very high reactivity to non-metals and to water. With water, they form alkalis hence the name alkalis. They are located at the far left of the periodic table.
Alkaline earth exhibit properties similar to alkalis except that they are harder and less reactive than the latter. are located to the right of the alkaline family.
Inert gases or rare gases are characterized by almost zero chemical reactivity to other elements. They enjoy very high chemical stability because of their saturated electronic layers. They are located in the last column of the table
Halogens are characterized by their high reactivity, which means that they are only found in the combined state in nature. They form salts with alkalis hence the Greek name “halogen” meaning “generators of salts”. They are positioned in the column left to the inert gases.
Hydrogen does not belong to any chemical family. It behaves like alkali and sometimes like a halogen. It sits above the alkali family.
The elements are distributed in the table in ascending order from left to right in horizontal lines, according to the atomic number (Z) of each element, which is above its symbol.
The periods indicate the number of layers or electronic levels that the atom has. For example, potassium (K) is located in the fourth period, and cesium (Cs), in the sixth period. This means that in electronic distribution, potassium has four layers or electronic levels and caesium has six.
Palladium (Pd) is an exception: despite being in the fifth horizontal line, it only has four layers or electronic levels.
The elements of the same period have the same number of electronic layers, which in turn is coincident with the number of the period. For example:
Note that in the periodic table there are 18 vertical lines or columns. They represent families or groups of chemical elements.
Above the columns are numbers (1, 2, 3, etc.).
Each column represents a family; for example:
1 is the family of alkali metals;
2 is the family donates alkaline earth;
18 is the family of noble gases.
Each chemical family groups its elements according to the similarity in properties. So with these other elements, from the same family, they have similarities in their properties.
The number of some families indicates how many electrons the chemical element has in the last layer of its electrosphere. Follow some examples below.
Sodium (Na) is in family 1, that is, it has an electron in the last layer of its electrosphere.
Magnesium (Mg) is in family 2, that is, it has an electron in the last layer of its electrosphere.
Aluminum (Al) is found in family 3, as this element has three electrons in the last layer of its electrosphere.
The chemical elements located in families 1 and 2 have the number of electrons in the last layer equal to the number of the family to which they belong.
For families 13 through 18, the number of electrons in the last layer is obtained, subtracting 10 from the family number. In other families, this rule cannot be applied.
Helium, despite being in the family 18, has only two electrons in the last layer, as this element has only two electrons.
The chemical family of the first column
The first column corresponds to the family of alkali metals
Lithium (Z = 3): it is the lightest of metals, it is used to manufacture cells and batteries, glasses and ceramics. Lithium batteries are found in many devices.
Sodium (Z = 11): it is found in the composition of cooking salt and is used for the manufacture of artificial indigo or to purify molten metals or in sodium vapour lamps.
Potassium (Z = 19): it is a very reactive metal and is used in the manufacture of fertilizers, it is also an essential nutrient for the human body.
Rubidium (Z = 37): it is a rare metal that is used in the manufacture of photoelectric cells or safety glasses.
Cesium (Z = 55): this is a rare metal that can be used in the manufacture of atomic clocks.
Francium (Z = 87): it is the heaviest of the alkali metals, it is radioactive.
These elements owe their name to their chemical properties: they can give strong bases when they are with water. They must therefore always be stored in oil so as not to cause reactions with the water. In this family, the global properties of the elements are very similar.
Be careful, hydrogen is not one of them!
All the elements in this column have an outer shell with an electron. They all form cations by losing an electron (Li +, Na +, K +, etc…) quite simply because they seek to obtain the most stable configuration, that of the nearest rare gas. Thus sodium will tend to ionize in Na + to resemble Neon, just as potassium will tend to ionize in K + to resemble argon.
Alkali metals represent an important part of the earth’s crust.
The chemical family of the second column
The second column corresponds to the family of alkaline earth metals
Beryllium (Z = 4): it is a fragile and toxic metal, it is used in certain alloys and is found in the composition of golf clubs.
Magnesium (Z = 12): it is a very abundant element on Earth, it is also essential for the proper functioning of the human body, it is part of the composition of alloys and is used in aeronautics thanks to its lightness.
Calcium (Z = 20): it is a very abundant element in the earth’s crust and it is essential for the development of the bone skeleton. Calcium is part of the composition of cement.
Strontium (Z = 38): it is a metal that ignites easily, it is used in fireworks or in ceramic varnishes.
Barium (Z = 56): barium ignites easily, it is used in pyrotechnics or radiology.
Radium (88): it is an extremely radioactive metal, it provides radon as a decay product. It is used in medicine for brachytherapy, it can be a tracer of contamination.
Free alkaline earth is never found in nature because they form a very reactive family.
All the elements of this family have two electrons on their outer shell. They can all form cations by losing two electrons (Be 2+, Mg 2+, Ca 2+, etc.).
The chemical family of the penultimate column
The penultimate column is that of halogens: it includes fluorine, chlorine, bromine, iodine and astatine. Each of these elements lacks an electron so that the last layer is complete and when they are transformed into ions they gain these electrons and form the F -, Cl -, Br -, I - and At - ions.
Fluorine (Z = 9): it is the most reactive of chemical elements, it is part of the composition of plastics and acts on tooth enamel.
Chlorine (Z = 17): it is very widespread in nature, it is a powerful biocide, it is used in the manufacture of bleach, it is also an element of the human body.
Bromine (Z = 35): it is scarce, it is used in medicine and has long been used for film photography.
Iodine (Z = 53): it is a rare element but essential for the proper functioning of the human organism, it is used in halogen lamps and in medicine.
Astatine (Z = 85): it is a rare and radioactive element, it is used in the medical and scientific fields.
Chemical families: last column
The last column corresponds to the family of noble gases (also called inert gases).
These gases are odourless, colourless and are not very reactive, which is why in the past they were called inert gases. They have very low boiling and melting points. All these elements were discovered at the end of the 19th century.
This family includes helium, neon, argon, krypton, xenon, and radon. The elements all have a complete outer layer which makes them (according to the duet and byte rules) very little reactive: they do not form ions and do not participate in any molecules.
Helium (Z = 2): very light and non-flammable gas, it is used in certain nuclear reactors, in the manufacture of telescopes or glasses. It is also the gas that is used to inflate the balloons that children love so much!
Neon (Z = 10): it is found in the form of traces in the atmosphere, it gives the colour red to neon lamps, it is also used in the manufacture of plasma televisions.
Argon (Z = 18): it is part of the earth’s atmosphere, it is used in the food industry but also for scuba diving.
Krypton (Z = 36): this gas is little used because it is expensive, nevertheless it is used for incandescent lamps and in double glazing.
Xenon (Z = 54): it is the rarest and the most expensive of the noble gases, it is used in lasers and plasma screens.
Radon (Z = 86): it is one of the densest elements capable of persisting in the form of gas. It is used in medicine and as a radioactive tracer.
The other families
The other families also have particular characteristics, we can mention some families to know:
In the middle of the table are the transition metals: these metals are less reactive than the alkali metals or the alkaline earth metals but they are good electrical conductors and they can be used in different alloys. Among them are chromium or manganese.
Metalloids (or semi-metals): these are non-metallic elements. This family is dispersed over columns 13 to 16. Among them, we find boron or silicon.
Lanthanides (or rare earth): these are elements contained in ores, among them we find cerium or lanthanum.
Non-metals: these are non-metallic elements that can be solid or gaseous and have poor thermal or electrical conductivity. Oxygen or sulfur are part of it.
Actinides: these are radioactive elements that are found abundantly in nature or that can be produced artificially. Among these elements are uranium or plutonium.
This table is also called the Periodic Table of the Elements because some atoms regularly exhibit similar properties due to their similar electronic configuration.
The table presents 7 rows called periods and 18 columns. These columns are designated by a Roman numeral (I, II…) and lowercase letters (a, b…).
The columns are used to classify the elements by family, according to the common characteristics of the atoms.
This table was last updated in 2016: the Periodic Table of the Elements currently has 118 elements.