In the periodic table of the elements, a period indicates the value of the principal quantum

number (n) for the outermost shells. Each period begins with the filling of principal

quantum number (n). The value of n for the sixth period is 6. For n = 6, azimuthal quantum

number (l) can have values of 0, 1, 2, 3, 4.

According to Aufbau’s principle, electrons are added to different orbitals in order of their

increasing energies. The energy of the 6d subshell is even higher than that of the 7s

subshell.

In the 6th period, electrons can be filled in only 6s, 4f, 5d, and 6 p subshells. Now, 6s has

one orbital, 4f has seven orbitals, 5d has five orbitals, and 6p has three orbitals. Therefore,

there are a total of sixteen (1 + 7 + 5 + 3 = 16) orbitals available. According to Pauli’s

exclusion principle, each orbital can accommodate a maximum of 2 electrons.

Thus, 16 orbitals can accommodate a maximum of 32 electrons.

Hence, the sixth period of the periodic table should have 32 elements.