What is the Difference Between Effective Nuclear Charge and Nuclear Charge?

The difference between effective nuclear charge and nuclear charge lies in the way electrons in an atom experience the attractive force of the nucleus. Here are the key differences:

• Nuclear Charge: This is the total positive charge of all the protons in the nucleus of an atom. It is represented by the atomic number (Z) and is the same for all electrons in the atom.
• Effective Nuclear Charge: This is the net positive charge experienced by an electron in a multi-electron atom. It is always smaller than the actual nuclear charge due to electron-electron repulsions. The effective nuclear charge depends on the type of electron and is experienced by the outer shell electrons.

The reason for the difference between nuclear charge and effective nuclear charge is that electrons in an atom do not all experience the same attraction towards the nucleus. Electrons in inner shells partially shield the outer electrons from the full nuclear charge, making the effective nuclear charge felt by the outer electrons smaller than the actual nuclear charge. As a result, the effective nuclear charge determines the size and energy of orbitals, which in turn influence important chemical properties such as the element's size, how easily it loses or gains electrons, and its electronegativity.

Comparative Table: Effective Nuclear Charge vs Nuclear Charge

Here is a table comparing the differences between effective nuclear charge and nuclear charge:

In summary, the effective nuclear charge (Zeff) is the net positive charge experienced by valence electrons in an atom, while the nuclear charge (Z) is the total positive charge of the nucleus. The effective nuclear charge takes into account electron shielding, which affects atomic sizes and ionization energies. On the other hand, the nuclear charge directly depends on the atomic number of the atom and influences physical and chemical properties of elements.