Question

why helium is placed in p block and group 18?​

Answer 1

Helium is having electronic configuration 1s² that is a configuration of s block element then it should be kept in s block. But it is not placed because of its properties only those match with inert gases.

• Helium is gas like other inert gases unlike solid s block metals.
• Helium is non- metal while s block contains only metals.
• Helium is much less reactive like other inert gases unlike s block metals which are most reactive.
• Helium also possess a completely filled electronic configuration like other inert gases. For all such reasons Helium is placed in inert gases group which lies in p block.

Answer 2

• He is a noble gas. It is called noble gas because it has a  stable electronic configuration.

• The electronic configuration of Helium is 1s².

• Despite its last electron entering in the s orbital, it is placed in p-block.

       This is because it has its duplet complete making it an inert gas.

• All the 18 group elements have a stable electron configuration which makes them inert.

     The properties of Helium resemble that of other 18 group elements.

Thus Helium is placed in group 18 with all other noble gases.