Question

Electronic configuration of element T is 2, 8, 7.

How many valence electrons are there in an atom of T?

• A. 1
• B. 5
• C. 3
• D. 7

Answer 1

Answer: (D)

7

Given $2,8,7$ in this first shell can have $2$ electrons where as second shell can have $8$ electrons $2$ in s orbital and $6$ in p -orbital. Hence remaining $7$ must be only in third shell as third shell has capacity of $18$ electrons.

Here in valence shell we have $7$ electrons in which $2$ are in s orbital and $5$ are in p orbital in which 1 is unpaired.Hence valency electrons is $7$ for atomic number $17$ that is chlorine.