Shielding Effect

[Rebekah_Park_2C]

I'm really confused about the shielding effect. Why are the valence electrons weaker and more positive? I thought electrons were always negative...

[Alex Nguyen 3I]

Shielding just means that in a multi-electron system/atom the electrons further away from the nucleus have a weaker attraction to the nucleus. The nucleus has less of a pull because other electrons closer to the nucleus repel the outer electrons (i.e. electron-electron repulsion). Valence electrons are more likely to be lost, gained, or bonded because of the weak pull. They're not positive though. Hope this helps.

[604599327]

Also, although the electrons are never positive, they do increase in energy as they move away from the center i.e. as n goes to infinity, E gets closer and closer to 0.

[Yunna Gu]

If you are more of a math person, here's the equation that explains why E gets closer to 0 as n increases: En=-hR/n^2

[Wesley Shen Lec 4]

I think Dr. Lavelle explained it like this: When the electron is infinitely far from the nucleus, the energy of the electron is 0 because it is not interacting with the nucleus. So if we take 0 as our reference state, as we get closer and closer to the nucleus, the electron goes into a lower and lower energy state. Since we started off at 0, the values will only get more negative.

[Dima Elhajjmoussa 3H]

Shielding affects the attraction the nucleus has towards the valence electrons. For example, as you go down a group, ionization energy decreases (the ability for an atom to gain an electron), because you have a higher atomic number and atomic radius increases, therefore you have more electrons in the orbitals. These electrons that are added will first fill up the energy level closest to the nucleus and then move out till the last shell (where the valence electrons are located), when you add these electrons you are adding core electrons and therefore the electrostatic attraction between the outermost electrons and the nucleus decreases and the nucleus no longer has a strong pull towards the valence electrons because its charge is being spread/consumed by the core electrons.

I really hope this helps, this concept may make more sense when Dr. Lavelle goes over electronegativity...