Explain the salient features of periods in the modern periodic table.

Explanation

Features of periods :
(i) The horizontal rows are called periods . There are seven periods in the periodic table .
(ii) First period ( Atomic number 1 and 2 ):
Shortest period
Contains only two elements (Hydrogen and Helium ) .
(iii) Second period (Atomic number 3 to 10):
Short period.
Contains eight elements (Lithium toNeon).
(iv) Third period (Atomic number 11 to 18):
Short period.
Contains eight elements (Sodium to Argon)
(v) Fourth period (Atomic number 19 to 36):
Long period.
Contains eighteen elements (Potassiumto Krypton). This includes 8 normal elements and 10 transition elements.
(vi) Fifth period (Atomic number 37 to 54):
Long period.
Contains 18 elements (Rubidium to Xenon). This includes 8 normalelements and 10 transition elements.
(vii) Sixth period (Atomic number 55 to 86):
Longest period
Contains 32 elements (Caesium to Radon). This includes 8 normal elements, 10 transition elements and 14 inner transition elements (Lanthanides)
(viii) Seventh period(Atomic number 87 to 118):
Like the sixth period, this period also accommodates 32 elements.
Recently 4 elements have been included by IUPAC.