What Is the Periodic Table?

1. The periodic table is a way of ordering the complete list of known elements according to their atomic number (in increasing order) and relevant chemical properties. In the tables, the rows are known as periods and the columns are known as groups.
2. The elements follow a Cartesian order horizontally (from left to right) and vertically (from top to bottom) according to atomic number: 
3. In the same group, the electrons of the elements follow the same valence configuration. This implies that they are similar in the chemical properties they express.
4. On the other hand, the elements of the same period order the number of valence electrons from lowest to highest. This means that as the energy level of the atom increases, so does the number of sublevels per energy level.
5. There are two fundamental divisions in the periodic table. In the first are the first 94 elements, which can be found in nature. The remaining 23 elements are not found in the environment and exist because they have been synthesized.
6. The modern periodic table is an improved version of certain earlier models. An example of another periodic table is the one developed by Dimitri Mendeleev. This table is based on discoveries made by other scientists such as Newlands and Lavoisier. 

Mendeleev’s Periodic Table

The father of the periodic table, Dmitri Mendeleev, is responsible for the first version of the periodic table that most closely resembles the one used today. In Mendeleev’s table, the basis on which the elements are ordered in increasing atomic mass. In the modern periodic law, the basis is the increasing order of atomic numbers. Mendeleev’s periodic table was based on the weight of the atoms. However, thanks to this table it was also possible to predict the discovery and properties of some elements. Mendeleev’s Periodic Table was first published in the German Journal of Chemistry in 1869. This first version contained about half of today’s elements, with a great deal of inaccuracy.

Long-Form of the Periodic Table

The modern periodic table has a long-form, which is based on the modern periodic law. In this table, the elements are arranged in increasing order according to their atomic numbers. The modern periodic table consists of 18 vertical columns and 7 horizontal rows.

Modern Periodic Table

1. The (vertical) columns are called groups in the modern periodic table. There are 18 groups in the table, numbered from 1 to 18. In each group are grouped the elements that have the same electronic configuration of the outer shell. 
2. On the other hand, the horizontal rows are called periods in the modern periodic table. Seven periods can be found in the periodic table. These are numbered from 1 to 7 from top to bottom. The first period consists of only two elements: hydrogen and helium.
3. The second and third periods are made up of a total of 8 elements each. Moving on to periods 4 and 5, there are 18 elements in each. In period 6 there are 32 elements. The 7th period of the table has had four new elements added: 113-Nihonium, 115-Moscovium, 117-Tennessine and 118-Oganese. With the new additions to this period, this row now contains 32 elements.
4. The periodic table has additionally, at the bottom, a separate panel. In this panel are the elements known as lanthanoids. Within this classification, 14 elements are belongingthere are 14 elements belonging to the 6th period. Finally, in the 7th period are the actinoids. In this category, there are 14 elements. Each period represents the energy levels present in the atoms of the elements.

The Cause of Periodicity in the Modern Periodic Table

1. In the modern periodic table, the external electronic configurations are repeated in certain uniform intervals.
2. For example, in group 1, we have alkali metals. These metals have the external electronic configuration ns1 (where n is the principal quantum number of the outer shell). This can be found in other groups. In fact, in group 17 the elements share a similar electronic configuration with formula ns2 np5. This means that they are similar in terms of properties. This group is known as halogens.
3. In group 18, the elements are configured as ns2 np6, having their orbitals fully occupied. These are known as noble gases or inert gases. Helium and argon belong to this group. Their characteristics are similar, and therefore, they are found together in the same group.
4. It can then be concluded that elements belonging to one group have similar properties to all the other elements in that group. Again, this is a consequence of the fact that they are very similar in their outer shell electron configuration.
5. Finally, another of the periodic properties of the modern table is valence. Using the valence electrons in the subshell as a basis, the periodic table allows the elements to be classified into different blocks: s, p, d and f.