These days, it’s hard to find a person, who has never heard about the periodic table or PT for short – the cornerstone of up-to-date chemistry. In this review we’ll tell about it a bit more than you might have expected.
We can define the periodic table as a tabular display of various chemical elements, specially organized in accordance with their atomic numbers, recurring chemical properties, and electronic configurations. Chemical elements are organized in order of growing atomic number, which is the number of protons. The standard form of the periodic table includes an 18 × 7 grid of elements, placed above a smaller double row of chemical elements.
One can deconstruct the periodic table into four rectangular blocks:
We call the rows periods. As for the columns of the d-,s- and p-blocks, they’re dubbed groups. Some of these groups even boast their own names, such noble gases or halogens.
The periodic table helps to explore obvious relationships between the properties of the chemical elements and even predict the properties of the new ones. With this table, one can easily analyze chemical behavior, so the periodic table is a must-have tool in chemistry.
All the versions of the periodic table include only chemical elements, so you won’t find compounds, mixtures or subatomic particles there. Every chemical element boasts a unique atomic number, which stands for the number of protons in the nucleus of this element. The vast majority of chemical elements feature different numbers of neutrons in different atoms and these variations are normally referred to isotopes. By the way, isotopes aren’t separated in the PT, they’re grouped together under a particular element. As for elements without stables isotopes, they feature the atomic masses of their steadiest isotopes.
In the periodic table, the chemical elements are organized in order of increasing their atomic number. A new row dubbed period begins when a new electron shell acquires its first electron. As for columns also dubbed groups, they’re determined by the atom’s electron configuration. Those elements, which share the same number of electrons in a certain subshell, find themselves in the same columns.
The chemical elements, having similar properties normally fall into the same group of the periodic table. So, it’s quite easy to foresee the chemical properties of a particular element if you know the properties of the chemical elements around it.
A vertical column in the periodic table is a group. Up-to-date quantum mechanical theories of atomic structure explain group trends by suggesting that the chemical elements in the same group should share the same electron configuration in the valence shell. This normally results in a shared trend in chemical properties with growing atomic number.
According to the international naming convention, the groups are numbered from one to eighteen in columns from left to right. The chemical elements belonging to the same group, are prone to demonstrating quite definite patterns in electronegativity, ionization energy and atomic radius.
When talking about a period in the PT, we mean exactly a horizontal row there. Though groups mostly have more considerable periodic trends, there’re certain regions where horizontal trends appear to be more crucial than vertical group trends, including the f-block, where actinides and lanthanides from two important horizontal series of chemical elements.
Atomic radius tends to decrease, when moving left to right across a period. This can be explained by the fact that every successive chemical element boasts an electron and proton. As a result, the electron gets drawn close to that atom’s nucleus. The given tumble in atomic radius also causes the ionization energy to surge, when moving from left to right in the period. Apparently, the more tightly bound the chemical element is, the more energy should be applied to remove an electron. Then, electronegativity grows in the same manner as ionization energy. It’s caused by the pull applied to the electrons by the nucleus.
The electron configuration is a crucial part of the periodic table. As we know, electrons are used to occupying corresponding electron shells. Every shell involves one or several subshells. Let’s call them p,s,d, g and f. As atomic number grows, electrons occupy these shells as well as subshells in accordance with the energy ordering rule or Madelung rule.
The history of the periodic table
Antoine Lavoisier in 1789 published a list of up to 33 chemical elements, where they were organized into groups of metals, gases, earths and nonmetals.
In the next century, scientists kept looking for more advanced classification scheme for the chemical elements. In 1829, Johan Wolfgang Dobereiner discovered that a great number of chemical elements could be successfully organized into triads, depending on their chemical properties.
In 1857, Jean-Baptiste Dumas issued a work, where he described relationships between groups of metals.
In 1858, August Kekule, a German chemist found out that carbon often boasted four other atoms firmly bonded to it. The given conception later became known as valency.
In 1862, a French geologist Alexandre-Emile Béguyer de Chancourtois published an early form of the periodic table dubbed the telluric helix. Frankly speaking, he appeared to be the first person who noticed the periodicity of the chemical elements. He arranged the chemical elements on a cylinder in a spiral by order of growing their atomic weight. Moreover, he added some compounds and ions.
In 1864, a German chemist, Julius Lothar Meyer created a table, including up to 44 chemical elements, organized in accordance with valency. The table stated that the chemical elements with similar properties had the same valency.
We’ve finally come up to the most well-known version of the periodic table - Mendeleev’s table. In 1869, Dmitri Mendeleev, a well-known Russian chemist published the first periodic table, where the chemical elements were listed in columns and rows according to their atomic weight.
By the way, the significance of atomic numbers to the organization of the periodic table wasn’t appreciated by the world of science until the very essence of neutrons and protons became clear.
Instead of atomic number, Mendeleev’s periodic table made use of atomic weight to group the chemical elements. Indeed, atomic weight sufficed in most cases, helping to predict the chemical properties of missing elements, while other methods weren’t effective enough in this regard. That substitution of atomic numbers gave a long-awaited definite sequence for the chemical elements.
In 1871, Mendeleev issued an updated form of its periodic table with new detailed predictions for the chemical elements.
As for the most common layout of the legendary periodic table, here we should be grateful to Horace Groves Deming, an American chemist. In 1923, he managed to create a medium and short forms of the periodic table.
With the development of up-to-date quantum mechanical theories of electron configurations in atoms, it became clear that every period of the periodic table corresponded to the certain filing of aquantum shell of electrons. In fact, larger atoms featured more electron sub-shells, respectively tables required longer periods.
In 1945, an American chemist, Glenn Seaborg offered a new version of the periodic table with the actinides belonging to the second f-block series. From this point of view, the actinide elements, including the lanthanides occupied an f-sub-level. Previously, the actinides were supposed to form the fourth d-block row. By the way, his colleagues recommended his not to publish this stuff as it could spoil his scientific career. Nevertheless, he dared to publish it and won the Nobel prize in 1951.
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