Question

Which of the following has largest size
H-
He
Li+
Be+2​

Answer 1

Answer:

H- is the answer because it is an isoelectronic species (exception)

Answer 2

The ion that has the largest size is H-.

• Down the group atomic size increases whereas atomic size decrease across the period.
• The atomic size of different elements and ions is differentiated based on the charge:size ratio. The higher the ratio higher is the size of the atom or ion.
• The size of the isoelectronic is determined by charge. The higher the positive charge smaller the size because it is peneterated to the nucleus more.
• H- has an extra electron so it faces repulsions. Hence, size of H- increases.
• Be2+, He, Li+ and H- all are isoelectronic and contain 2 electrons.