Electronic configuration of Hydrogen
Atomic number of hydrogen = 1
Therefore number of electrons = 1
Maximum number of electrons in 1st orbit = 2
Since, hydrogen has only one electron, therefore, it will reside in 1st orbit.
Thus electronic configuration of hydrogen
Number of orbit present in hydrogen = 1
Electronic configuration of Helium
Atomic number of helium = 2
Therefore number of electrons = 2
Therefore, electronic configuration of helium is
Number of orbit in helium atom = 1
Electronic configuration of Lithium
Atomic number of Lithium = 3
Therefore number of electrons = 3
Since the maximum number of electrons in 1st orbit is equal to 2, therefore, after accommodating 2 electrons in 1st orbit, the third electron will go in 2nd orbit.
Thus, electronic configuration of lithium is
Number of orbit in Lithium atom = 3.
