What is the next atomic orbital in the series below? 1s, 2s, 2p, 3s, 3p, 4s, a. 3d b. 4d c. 4p d. 5s

A) 3d

Explanation:

To know how to fill atomic orbitals, you have to use the Aufbau Principle. Aufbau Principle, which is also called Building-up Principle, states that electrons fill orbitals in order of increasing energy.

Madelung´s Rule also helps us to determine the energy level of each orbital and besides, the order to filling them. It claims that:

The first number of each orbital is n, the principal quantum number. Then l takes values of 0, 1, 2 and 3, according to the orbital letter:

Let´s calculate n+l values in this exercise:

As 2p and 3s have both n+l=3, we use the second statement of Madelung´s Rule to determine the orbital which fills first (that with lower energy), and so, 2p fills before 3s as it has lower n value.

Now, let´s calculate n+l values for the possible answers:

Answer B) isn´t correct because 4d is the orbital with the highest n+l value, so the highest energy level and the last orbital in the answers that must be filled.

For answers A), C) and D), as they have identical n+l values, it´s necessary to use the second statement of Madelung´s Rule again. Increasing in n shows the order of increasing energy and the correct order of filling orbitals. So, 3d orbital (answer A) must be filled first than 4p and 5s, as well; and of course, as we said before, 3d orbital must be also filled before 4d.

The correct answer is A) 3d.

the answer is a and have a great day