Question

Write the atomic number of the element present in the third period and seventeenth group of the periodic table.

Answer 1

There are two elements in the \(1^{st}\) period and eight elements in the \(2 ^{nd}\) period. The third period starts with the element with \(Z = 11\). Now, there are eight elements in the third period. Thus, the 3rd period ends with the element with \(Z = 18\) i.e., the element in the \(18^{th}\) group of the third period has \(Z = 18\). 

Hence, the element in the \(17^{th}\) group of the third period has atomic number \(Z = 17\).