the unconditional guru

The number of valence electrons in phosphorus is generally 5 and it requires 3 more electrons to complete its octet.

but it has an empty d-sub shell in which its electrons can excite and increase its valency from 3 to 5.

in the above picture you can easily understand in case of phosphorus , the electron from s-subshell jumps to the empty d-subshell .

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