Explain the concept of effective nuclear charge in bonding.

Effective nuclear charge refers to the net positive charge experienced by an electron in a multi-electron atom.

In more detail, the concept of effective nuclear charge is a fundamental principle in understanding the structure and behaviour of atoms in chemical bonding. It is based on the idea that the net positive charge experienced by an electron in a multi-electron atom is less than the actual nuclear charge due to electron-electron repulsion. This means that the outer electrons are not as strongly attracted to the nucleus as they would be in a single-electron atom.

The effective nuclear charge can be calculated using Slater's rules, which take into account the shielding effect of inner electrons. The shielding effect refers to the phenomenon where inner electrons shield outer electrons from the full positive charge of the nucleus. This is because the negatively charged electrons repel each other, reducing the overall attractive force from the positively charged nucleus.

The concept of effective nuclear charge is crucial in explaining trends in the periodic table, such as atomic radii, ionisation energy, and electron affinity. For instance, as you move across a period from left to right, the effective nuclear charge increases because the number of protons in the nucleus increases, while the shielding effect remains relatively constant. This results in a stronger attraction between the nucleus and the outer electrons, leading to smaller atomic radii.

Similarly, the increase in effective nuclear charge across a period also explains the increase in ionisation energy. As the effective nuclear charge increases, the outer electrons are held more tightly to the nucleus, making it more difficult to remove an electron and thus increasing the ionisation energy.

In summary, the concept of effective nuclear charge is a key factor in understanding the structure of atoms and their behaviour in chemical bonding. It provides a quantitative measure of the net positive charge experienced by an electron in a multi-electron atom, taking into account the shielding effect of inner electrons. This concept is fundamental in explaining various trends in the periodic table.