The trend on the periodic table is to increase across a period and increase down a group. Effective nuclear charge refers to the charge felt by the outermost valence electrons of a multi electron atom after the number of shielding electrons that surround the nucleus is taken into account. Except for hydrogen z eff is always less than z and z eff increases from left to right as you go across a row.
Relationship between the effective nuclear charge z eff and the atomic number z for the outer electrons of the elements of the first three rows of the periodic table. The term effective is used because the shielding effect of negatively charged electrons prevents higher orbital electrons from experiencing the full nuclear charge. The effective nuclear charge often symbolized as z eff or z is the net positive charge experienced by an electron in a multi electron atom.
Electrons that are closer to the nucleus which are referred to as inner or core electrons effectively cancel some of the attraction of outside or valence electrons to the nucleus. The effective nuclear charge is then the net electric field that a particular electron experiences. Hence the electrons will cancel a portion of the positive charge of the nucleus and thereby decrease.
If an electron is far from the nucleus i e if the distance r between the nucleus and the electron is large then at any given moment many of the other electrons will be between that electron and the nucleus figure pageindex 1. Electron shielding and effective nuclear charge. The effective nuclear charge may be approximated by the equation.
The effective nuclear charge is the net charge an electron experiences in an atom with multiple electrons. In general for any many electron atom any particular electron will always be screened from the nucleus to some extent by the remaining electrons. The difference between the full nuclear charge z and the screening effect of the inner two electrons is called the effective nuclear charge or z eff.
The effective nuclear charge often symbolized as or is the net positive charge experienced by an electron in a polyelectronic atom the term effective is used because the shielding effect of negatively charged electrons prevents higher orbital electrons from experiencing the full nuclear charge of the nucleus due to the repelling effect of inner layer electrons.
