Kim Lor

Sarah Murray

November 9, 2009

• Definition: the strength of the interaction between two electrical charges depends on the magnitude of the charges and the distance between them

• Between an electron and the nucleus, this means the magnitude of the net nuclear charge acting on the electron and the distance between the two.

As nuclear charge increases, force of

attraction increases.

As the distance between the electron and nucleus

increases, force of attraction decreases.

• Each electron is simultaneously attracted to the nucleus as it is repelled by the other electrons

• The inner electrons between the nucleus and the electron in question make up the shield or screen, blocking energy from reaching that outer electron.

• The shield between the nucleus and the electron is the primary influence on the effective nuclear charge

• Effective nuclear charge: charge felt on valence electrons

interest

Zeff = Z – S

• Zeff effective nuclear charge

• Z protons in the nucleus

• S average number of electrons that are between the nucleus and the electron in question• S is an average (it does

not need to be an integer)

• Use the nuclear charge (number of protons) and the number of core e-

• Ex: Magnesium([Ne] 3s2)• [Ne] core = 10- (e-)• Nucleus = 12+ (p+)• 12 – 10 = +2

• However! The 3s e- have some probability of being inside the core, therefore making the screen less effective, so the energy reaching the 3s e- is probably greater than 2+.

• Zeff > 2+• Note: this is important because in

reality, Mg’s valence e- have a charge of 3.3+.

Calculate the effective nuclear charge of Gallium

• Ga valence shell: 4s24p1

• [Ar] core = 28- ; nucleus = 31+

• 31 – 28 = +3 Zeff > 3+

On the board:

Calculate the effective nuclear charge of

Polonium

List the nuclear charge, the charge of the core, and the e- in the valence shell.

Answer: > Zeff 6+

• Zeff increases as you move horizontally across the periodic table (same shielding, nuclear charge)

• Zeff slightly increases down a family because larger electron cores are less able to screen the outer electrons from the nuclear charge• Not nearly as significant as

across the row

Works Cited

Brown, Theodore L., et al. “7.2 Effective Nuclear Charge.” Chemistry the Central Science. Upper Saddle River, New Jersey: Pearson Education, 2003. 239-41. Print.

Francis, Eden. “Effective Nuclear Charge.” Periodic Table and Atomic Properties. Clackamas Community Coll., 2002. Web. 8 Nov. 2009. <http://dl.clackamas.cc.or.us/ch104-06/efffective_nuclear_charge.htm>.

“Periodic Trends.” CH 412 Advanced Inorganic Chemistry. Western Oregon U, 1997. Web. 8 Nov. 2009. <http://www.wou.edu/las/physci/ch412/Periodic%20trends/periodic_trends.htm>.