Periodic Table
The Periodic table, also known as the periodic table of chemical elements is a tabular format display of all chemical elements where they are organised in rows and columns. The table is used in physics, chemistry and all other sciences to refer to the properties of chemical elements such as the atomic number and atomic mass. The arrangement of these elements also shows some helpful trends such as ionisation energy, electronegativity and atomic radius.
Different scientists over time have improved our understanding of the arrangement of elements, most recent standardised upgrade was defined in 1869 by Dmitri Mendeleev, also known as “The father of modern periodic table” published the first version of the periodic table. This table was based on characterisation by atomic mass, and although there were gaps in the table due to some unidentified elements, Mendeleev successfully explained their properties too.
The table consists of rows which are called periods and columns which are called groups. It is divided roughly into four blocks: s,p,d and f-blocks. There are a total of 118 elements shown in the table and only 94 of them exists in nature while others can be synthesized in the laboratory. Of these 94 elements, only 8 are stable and three undergo radioactive decay (bismuth, thorium and uranium). All 24 artificial elements known to us so far are radioactive. The table is based upon periodic law which states that: “The properties and atomic structures of chemical elements are periodic functions of their atomic numbers”. All the elements are placed in the periodic table according to their electronic configuration.
Chemical reactions usually involve valence electrons so the elements with similar outer electronic configurations are placed in the same group as they are expected to react similarly. Some important properties that we get to know through the periodic table are:
- Atomic radius: It is the size of the atoms and follows a decreasing trend while going left to right along with the main-group elements. This is because even after having the same electrons in the outer shell, the nuclear charge increases. Now, while going down the column, the atomic radius increases as the outer electrons are in higher shells and thus further away from the nucleus.
- Ionisation energy: It is the energy needed to remove an electron from the atom. Ionisation energy follows an increasing trend from left to right and up to down as the electrons closer to the nucleus are held more tightly and are more difficult to remove.
- Electron affinity: This property is the opposite of the ionisation energy, it is the energy released when adding an electron to the atom. Electron affinity follows the increasing trend from down to up and right to left as an electron will be strongly attracted to an atom if it is pulled from its nucleus more easily.
- Electronegativity: Atoms are capable of forming covalent bonds by sharing pairs of electrons resulting in an overlap orbital. Now, the degree to which an atom can attract pairs of shared electrons depends on its electronegativity which is the tendency of an atom to lose or attract electrons. More electronegative atom attracts more electrons and vice versa.
