What causes shielding effect?

Question

Lucy Alessi · Accepted Answer

A greater number of electron between the nucleus and the electron in question.

To understand the shielding effect, consider #Z#eff or the effective nuclear charge. The value of #Z#effective will stay constant as you go across a period and increase as you travel down. Why do you think this is? To understand this, try think of the atomic orbital theory. Remember that #Z#eff = Z - S where S is the number of electrons between the valence electron and the nucleus and Z is the atomic number. What makes cesium a bigger element than potassium, for instance? Cs = #1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^6 5s^2 4d^10 5p^6 6s^1# K = #1s^2 2s^2 2p^6 3s^1 3p^6 4s^1# As you can see there are more orbitals separating the valence electrons from the nucleus of the atom, so the nucleus will have less control of the #6s^1# electron than it will of the #4s^1# electron. This is the shielding affect.

Nicholas Antonuccio · Answer

undefined The shielding effect is caused by the presence of inner electron shells in an atom. These inner electron shells partially shield the outermost electrons from the full positive charge of the nucleus, reducing the attraction between the nucleus and the outer electrons. As a result, the outer electrons experience a weaker effective nuclear charge, leading to a decrease in their attraction to the nucleus and an increase in atomic size.