Zeff, also known as effective nuclear charge or effective atomic number, refers to the net positive charge experienced by an electron in an atom. It takes into account both the actual positive charge of the nucleus and the shielding effect caused by other electrons in inner energy levels.
The concept of Zeff can influence electron affinity, which is the energy change that occurs when an atom gains an electron to form a negative ion. Electron affinity is influenced by several factors, and Zeff is one of them. Here's how Zeff affects electron affinity:
Effective nuclear charge (Zeff) and electron affinity: In general, as the effective nuclear charge increases, the attraction between the nucleus and the incoming electron also increases. This enhanced attraction tends to increase the electron affinity. When Zeff is high, the valence electrons experience a stronger pull from the nucleus, making it more favorable for the atom to gain an additional electron.
Shielding effect: The shielding effect occurs when inner electrons repel or shield the valence electrons from feeling the full positive charge of the nucleus. This reduces the effective nuclear charge experienced by the valence electrons. If the shielding effect is significant, the valence electrons are less strongly attracted to the nucleus, leading to a decrease in electron affinity.
It's important to note that Zeff is not the sole determinant of electron affinity. Other factors, such as electron-electron repulsion, electron orbital stability, and the overall electronic configuration of the atom, also play a role. Electron affinity trends can vary across different elements and groups of the periodic table.
In summary, as Zeff increases, the effective attraction between the nucleus and the incoming electron strengthens, typically resulting in an increase in electron affinity. However, the shielding effect caused by inner electrons can counterbalance this effect, leading to more complex electron affinity trends across different elements.