The Periodic Table and Periodicity of Elements

In the later part of the 19th century, the works of chemists such as Newland, Lother and most especially Mendelev, eventually led to what is today known as the Periodic Table. Their work showed that there exist the occurrence at regular intervals, with increasing atomic weights, of similar properties amongst the then known elements – this is called periodicity.

Mendelev later designed a table of 7 rows (periods) and 8 vertical columns (groups) in which the then discovered elements were assigned.

Spaces were left for predicted elements to be assigned when eventually they were discovered – he was right, the spaces were filled up with elements which became known later. This table is the periodic table.

The periodic law – the modern periodic law states that the properties of elements are periodic function of their atomic numbers.

The periodic table can be divided into several classes based on the outermost orbitals of the electronic configuration of its elements. Hence, groups IA and IIA are called the s - block elements. They have 1 and 2 electrons in the s orbital, which is the outermost orbital in their outermost shells respectively.

Groups IIIA to 0 are called the p – block elements (their electronic configurations show their outermost orbitals to be the p – orbital). The bridge-like arrangement of elements (elements in-between groups IIA and IIIA - i.e. the B group elements) contains the transition metals – they are the d – block elements (their outermost orbitals are the d orbitals which are partially filled).

Elements in the same group show similar electronic configuration, i.e., they possess the same number of electrons (corresponding to their group number) in their outermost shells, and contain the same number of electrons in their outermost orbitals (which are of the same kind).

For example, in group IA, hydrogen, lithium, sodium and potassium all have 1 electron in their outermost shells, which is accommodated in their s orbitals; in group VIIA, fluorine and chlorine contain seven electrons in their outermost shells, with five in the outermost p orbitals.

Note: * It is because of the similarity in electronic configuration that all members of a group possess similar chemical properties (members of the same group use equal number of electrons from the same kind of orbital to effect chemical reactions).

* The repetition of properties of elements with increase in atomic number (i.e. periodicity) is as a result of repetition of the same order of electronic configuration (i.e., electronic configurations in the outer shells are repeated.

Also see:

Variation in Physical Properties of Elements Across the Periodic Table
Properties of Alkaline Metals
Properties of Alkaline Earth Metals
Properties of Noble Gases