Calculate the effective nuclear charge of the last electron in an atom whose configuration is 1s^2 2s^2 2p^6 3s^2 3p^5.

To calculate the effective nuclear charge experienced by the last electron in an atom, you need to consider the atomic number (Z) and the electron configuration. The effective nuclear charge (Zeff) is a measure of the net positive charge experienced by an electron in an atom, taking into account the shielding or screening effect of inner electrons.

The electron configuration you provided is for an atom with Z = 16 (sulfur). Here's the breakdown of the electron configuration:

1s² 2s² 2p⁶ 3s² 3p⁵

Now, let's calculate the effective nuclear charge (Zeff) for the last electron, which is in the 3p orbital.

Determine the total number of electrons in the atom (Z = 16), including the 3p electron:
Z = 1s² + 2s² + 2p⁶ + 3s² + 3p⁵ = 2 + 2 + 6 + 2 + 5 = 17

Identify the number of inner electrons that shield or screen the 3p electron from the nucleus. These are the electrons in the 1s², 2s², 2p⁶, and 3s² orbitals. So, there are 2 + 2 + 6 + 2 = 12 inner electrons.

Calculate the effective nuclear charge (Zeff) using the formula:
Zeff = Z - Inner Electrons
Zeff = 17 - 12 = 5

So, the effective nuclear charge experienced by the last electron in this sulfur atom is 5.