Question

An element 'X' has mass number 35 and number of neutrons 18. Write atomic number and electronic configuration of 'X'. Also write group number, period number and valency of 'X'.

Answer 1

X has mass number = 35 , no. of neutrons = 18
Atomic no. = Mass number - No. of neutrons
Atomic no. of X = 35 -18 = 17
Hence element X has atomic no. = 17
Electronic configuration = 2, 8, 7
Group number = 17 (10+ no. of valence electrons so 10+ 7 = 17)
Period number = no. of shells = 3
Valency = 1 as X will gain one electron to complete its octet.