Question

Why are the groups 1,2,13,14,15,16,17,18, are called representative elements

Answer 1

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ELEMENTS



       The modern periodic table was constructed by the Russian chemist Dmitri Mendeleyev in 1869. The modern periodic table consists of horizontal rows called periods and vertical columns calledgroups. These are discussed below: 

Groups in Modern Periodic Table

       A group may be defined as vertical column in the periodic table. In terms of electronic structure of the atom, a group constitutes a series of elements whose atoms have the same outermost electronic configurations. There are 18 groups in the long form of the periodic table. According to the new recommendations of international Union of Pure and Applied Chemistry (IUPAC), the groups are numbered from 1 to 18. 

       Each group contains elements that tend to react chemically in similar ways, because they all have atoms in which the arrangement of electrons around the nucleus is similar. Some groups in the periodic table are given special names e.g. 

       Group 1        the alkali metals

       Group 2        the alkaline earth metals

       Group 15       the pnicogens

       Group 16       the chalcogens

       Group 17       the halogens

       Group 18       the noble gases





Representative elements in modern periodic table

       The first two groups on the extreme left and last six groups on the extreme right involve the filling of s- and p- orbitals, respectively, These groups represent the main groups of the periodic table and are numbered as 1, 2, 13, 14, 15, 16, 17 and 18. The elements present in these groups are known asnormal elements or representative elements.

Transition series elements in modern periodic table

       The ten groups lie in between first two and last six groups i.e. between group 2 and group 13. These are numbered from 3 to 12. The elements present in these groups are called transition elements. The name is derived from the fact that they represent transition (change) in character from reactive metals (elements of groups 1 and 2) on one side to the non-metals (elements of group 13 to 18) on the other side. 

Inner transition series elements in modern periodic table

       There are two more rows at the bottom of the periodic table. These rows consist of fourteen elements after lanthanum (Z = 57) and fourteen elements which follow actinium (Z = 89). These are placed separately in the periodic table to save space and avoid undue sidewise expansion of the periodic table. The elements in the first row, starting from cerium are called lanthanoids (or lanthanides) and the elements present in the second row starting from thorium are called actinoids (or actinides). These lanthanoids and actinoids together are called inner transition elements .




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Answer 2

Explanation:

According to the Aufbau principle, in the ground state of an atom or ion the electrons fill atomic orbitals of the lowest energy levels first, before filling the higher energy levels.

So, in groups 1,2,13,14,15,16,17,18 the electrons fill in the orbitals of each element according to the Aufbau's principle. Also, the number of valence electrons present in the elements of these groups represents their respective group.

That is why, they are called representative elements as valence electrons present in their elements represent their respective group.