Effective Nuclear Charge

[Eden Breslauer-Friedman 2A]

I saw the term "Effective Nuclear Charge" used in the sapling homework, and realized it was something Dr. Lavelle talked about in lecture. I understand that inner electrons shield the outer electrons from the electrostatic charge of the positive nucleus, and are therefore held less tightly. In lecture, Dr. Lavelle explained that because of this, the outer electrons feel a reduced electrostatic attraction.

How does an effective nuclear charge relate to this concept? What does it really mean?

Thank you!

[Maaria Abdel-Moneim 2G]

Effective nuclear charge is basically the positive charge from the nucleus that the electrons feel. The higher the effective nuclear charge the higher the positive attractive positive charge is from the nucleus therefore the electrons are held more tightly. This is why atomic radius decreases and ionization increases as you go across the periodic table. Hope this helps!

[Nathan Lao 2B]

I like to think of effective nuclear charge as " the more protons in an atom, the stronger the pull," where "the pull" is the electrostatic attraction between the nucleus and electrons that Professor Lavelle mentioned. Essentially, it's the positive charge/attraction of the nucleus in relation to the electrons.

[Vince Li 2A]

Effective Nuclear Charge basically means the force the electron feels due to how the positively charged nucleus pulls the electrons towards it. However, because there are other electrons nearby, they essentially shield each other from the pull of the nucleus. I just searched this up, but the effective nuclear charge is the net positive charged experienced by an electron, due to how the core electrons shield another electron from the pull of the nucleus. The equation for it is Zeff = Z - S, which is the atomic number - the number of shielding electrons.

[JoshMoore2B]

I saw the term "Effective Nuclear Charge" used in the sapling homework, and realized it was something Dr. Lavelle talked about in lecture. I understand that inner electrons shield the outer electrons from the electrostatic charge of the positive nucleus, and are therefore held less tightly. In lecture, Dr. Lavelle explained that because of this, the outer electrons feel a reduced electrostatic attraction.

How does an effective nuclear charge relate to this concept? What does it really mean?

Thank you!

The other posts did a good job explaining the idea, and I wanted to give a little more of a numerical example.

Suppose you have you have potassium, which has 19 protons. Its nucleus, then, has a charge of +19. Naturally, then, each electron should feel a force related to that +19 charge that attracts it to the nucleus. I will call this the absolute nuclear charge.

As you said, some of the inner electrons shield some of the outer electrons from this, and so the outer electrons feel a reduced electrostatic attraction. Numerically, this can be understood that instead of that +19 charge affecting the outer electrons, they might instead feel a +18 or a +17 or a +15 or a +13 charge (it wouldn't likely be so dramatic, but the idea is that they would feel a lesser charge) because of this shielding. This +18 or +17 (the lower number that the outer electrons feel) is the effective nuclear charge, because the strength of the net attractive force the outer electrons are experiencing has a magnitude equal to if they were to feel an unshielded +18 or +17, for example.