Class 9 Science
Atomic number of aluminium = 13.
Therefore number of electrons = 13.
Thus, electronic configuration of aluminium is 
Number of orbit in aluminium = 3
Atomic number of silicon = 14
Therefore number of electrons = 14
Thus, electronic configuration of silicon is 
Number of orbit in silicon = 3
Atomic number of phosphorous = 15
Therefore number of electrons = 15
Thus, electronic configuration of phosphorous is 
Number of orbit in phosphorous = 3
Atomic number of sulphur = 16
Therefore number of electrons = 15
Thus, electronic configuration of sulphur is 
Number of orbit in sulphur = 3
Atomic number of chlorine = 17
Therefore number of electrons = 17
Thus, electronic configuration of chlorine is 
Number of orbit in chlorine = 3
Atomic number of argon = 18
Therefore number of electrons = 18
Thus, electronic configuration of argon is 
Number of orbit in argon = 3
Atomic number of potassium = 19
Therefore number of electrons = 19
Since, maximum number of electrons in outermost orbit will not be more than 8, thus the 19th electron of potassium atom will reside in 4th orbit.
Thus, electronic configuration of potassium is 
Number of orbit in potassium = 4
Atomic number of calcium = 20
Therefore number of electrons = 20
Thus, electronic configuration of calcium is 
Number of orbit in calcium = 4
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