An Introduction to the Periodic Table

The periodic table is a great achievement of organized chemical information. It contains a list of all the chemical elements organized based on atomic number, electron configuration and occurring chemical properties. It´s called the periodic table because the way in which the elements are arranged can predict the properties of existing or new elements. The periodic elements can be in their solid, liquid or gaseous state at room temperature. There are 92 naturally found elements and a number of synthetic (man-made) elements in the periodic table. They all are arranged based on their chemical and physical properties. The elements contained in the periodic table comprise the chemical blocks found in the whole universe.

The elements in the periodic table are arranged into periods, which correspond to the rows and groups, corresponding to the columns in the table. The standard periodic table is arranged in 18 columns and 7 rows. The standard periodic table is also divided into four distinct blocks; the s block, which is situated at the left of the table; the p block to the right; the d block in the middle; and the f block, which contains the lanthanides and actinides. The periodic table defines recurring chemical properties of existing, new, undiscovered or synthesized elements.


A group in the periodic table is a vertical column. The groups are numbered from 1 to 18 from left to right. The roman numbers on top of each column correspond to the number of valence electrons in each of the elements in that group. A group or family usually has the same electron configuration in their outer shell. Elements of the same group tend to show similar patterns in atomic radii, electronegativity and ionization energy. The atomic radii increase from top to bottom in a group. Similarly, the ionization energy decreases from top to bottom, since the valence electrons are less tightly bound to the nucleus. The electronegativity also decreases from top to bottom, due to this trend.


Periods are configured in rows along the periodic table. The elements in a row exhibit trends in atomic radius, electron affinity, ionization energy and electronegativity. From left to right along a row, the atomic radius of the elements decreases, due to the added protons and electrons in each successive element, which attract the electron closer to the nucleus. This trend also requires more energy to remove an electron, thus, the ionization energy increases from left to right. Electronegativity also increases due to the attraction exerted on the electrons by the nucleus. Electron affinity increases from left to right, with the metals having a lower electron affinity than the nonmetals. Each new period, which starts in the group of the alkali metals, corresponds to a new shell that is occupied by an electron.


Some sections of the periodic table are categorized as blocks. This stems from the configuration of the outermost electron shell. Thus, each block is named based on the subshell in which the valence electron is located. The s block includes the leftmost groups, including the alkali and alkaline earth metals. This block also includes hydrogen and helium. The p block groups 13-18, which contain the nonmetals and metalloids. The d block is composed of groups 3-12 and includes all the transition metals. The f block, which is usually located at the bottom of the periodic table, contains the lanthanides and actinides. Some tables include the f block inside the main table, while in the standard periodic table, it is separated. 

The properties of the elements show recurring patterns or periodicity. This recurring behavior is what led to the creation of the periodic law and the creation of the first periodic table. Dmitri Mendeleev, who developed the first recognized periodic table of elements, published it in 1869. Most of Mendeleev’s predictions about the properties of unknown elements which were supposed to fill the gaps in the table were proven correct when these elements were subsequently discovered.