Calculate the effective nuclear charge experienced by the 4s electron in potassium atom(Z = 19.

The effective nuclear charge experienced by an electron in a multi-electron atom is the net positive charge felt by that electron due to the nucleus after accounting for the shielding or screening effect of other electrons. It is also known as the "effective charge" or "net charge" that the electron experiences.

The effective nuclear charge (Zeff) can be calculated using Slater's Rules, which provide a way to estimate the shielding effect of inner electrons on outer electrons. According to Slater's Rules:

For each inner-shell electron, the contribution to shielding is set as follows:

Full shielding for electrons in the same shell.
Partial shielding of 0.35 for electrons in the preceding shell.
No shielding for electrons in earlier shells.
For outer-shell electrons, the sum of the shielding constants of all inner-shell electrons gives the effective nuclear charge (Zeff).

The electron configuration of a potassium (K) atom is: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹.

Using Slater's Rules, we can calculate the effective nuclear charge experienced by the 4s electron in a potassium atom (Z = 19):

The 1s² electrons provide full shielding (1 × 2 = 2).
The 2s² and 2p⁶ electrons provide partial shielding (0.35 × 8 = 2.8).
The 3s² and 3p⁶ electrons provide no shielding.
Adding these contributions: 2 (full shielding) + 2.8 (partial shielding) + 0 (no shielding) = 4.8.

Therefore, the effective nuclear charge (Zeff) experienced by the 4s electron in a potassium atom is approximately 4.8.

Keep in mind that this is a simplified estimation and actual quantum mechanical calculations can give more precise values.