In which orbital does an electron in a cesium atom experience the greatest effective nuclear charge?

The effective nuclear charge in a cesium atom is greatest in the 1s orbital

Explanation:

Effective nuclear charge (Zeff) is the positive nuclear charge that is experienced by an electron in an atom. It is affected by the shielding effect and penetration of electrons of the atoms.

The shielding effect is the decrease in attraction between an electron and the nucleus in any atom with more than one electron shell. Innermost electrons shield the outermost electrons from the positive charge of the nucleus. The more electron shells there are, the greater the shielding effect experienced by the outermost electrons. and the more electron shielding an electron has, the lower the Zeff value.

Penetration is the ability of an electron to approach the nucleus. The closer the electron is to the nucleus, the higher the penetration. Electrons with higher penetration will shield outer electrons from the nucleus more effectively. The s orbital being closest to the nucleus has the highest penetration while the f orbital has the lowest penetration.

Cesium has an atomic number of 55 as well as nuclear charge of +55. It has 54 electrons in its filled 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s²4d¹⁰5p⁶6s¹ shells and an outermost 6s electron. Based on the explanation above, the effective nuclear charge is greatest in the innermost 1s orbital and least in the outermost 6s orbital.