Arrangement of elements as per the increasing atomic number (protons) incidentally reflects the
electronic configuration of elemental atoms. Number of protons in the nucleus of an atom is, called as ‘Atomic Number’. In a neutral atom, number of protons or atomic number will also be equal to the number of electrons. Fixed number of electrons is, distributed in subshells of varying distance around the positively charged nucleus. Number of shells, subshells and the maximum electrons that can present in them are, limited by the quantum nature of the electrons.
Sub-shells and the maximum number of electrons arranged in terms of increasing energy is given as-
1s2 2s22p6 3s23p6 4s23d104p6 5s24d105p6 6s24f145d106p6 7s25f146d107p6
Arrangement of elements in the modern periodic table and consequent similarity of properties of elements, is because of their similarity in electronic configuration of having same number of valence electrons.
- First period contains two elements, corresponding to the filling up of 1s1 and 1s2 configuration.
- Second & third period have eight elements each filling up of subshells of s2p6 configuration.
- Fourth and fifth have 18 elements, each filling up the sub shells of s2d10p6
- Sixth and seven period have 32 elements, filling up the subshells of s2f14d10p6
- Fourteen elements filling up the f-subshell in the sixth and seventh period are, written separately. Fourteen elements following Lanthanum are, called lanthanides and similarly, fourteen elements following actinium are, called actinides.
Physical properties of elements are, controlled by the nuclear mass, while chemical properties are determined by the valence electrons. Modern periodic table helps in further classification of
Elements in terms of electronic configuration. Elements are, classified in to four main groups as:
üs-block elements, whose valence electrons fill up the s-subshell. s- block elements are of two types – Group 1- Alkali metals and Group 2 -Alkaline earth metals
üp-Block elements, where their valence electrons fill up the p-subshell. p-Block elements are of six types – They belong to the group 13 to 18. Each, group is known by a family name.
- Group 13 as Boron family
- Group 14 as Carbon family
iii) Group 15 as Pnictogen family
- Group 16 as chalcogens family
- Group 17 as Halogens family and
- Group 18 as Noble or Inert gases
d-Block elements, have variable electronic configuration of s1-2d1-10 generally filled s-subshell and electrons filling d-subshell. The elements are also called as transition elements.
f-Block elements, have electrons filling the f-subshell and have a configuration of s2d0-1f1-14.
f-block elements have other names a Lanthanides and Actinides and written at the bottom of the periodic table.
Modern periodic table is useful in understanding the trends in both physical and chemical properties
- Like atomic radii, ionization potential, electron affinity, electronegativity, melting& boiling points,
- Metallic & non-metallic nature, chemical reactivity, nature and chemical nature of their compounds of elements both along the period and along the group.
- Demarcation of elements with electropositive metals – metalloids- electronegative non-metals is obvious.
- Each period indicate the addition of new shell and hence increased atomic radius and volume.
- Trend in the change of properties can be, judged from the increase in the nuclear charge and radius.