Question

effective nuclear charge down a group question!

Answer 1

Decrease down a group (although nuclear charge increases down a group, shielding effect more than counters its effect). source: http://wiki.ubc.ca/Effective_Nuclear_Charge_-_Definition_and_Trends

Answer 2

anyone care to explain WHY shielding effect more than counters its effect? to quote ..

Answer 3

BEC. ON GOING DOWN THE GROUP,
THE NO OF INTERVENING ELECTRONS INCREASE GREATLY AND ALSO THE SIZE OF THE ATOM INCREASES...

BOTH THESE THINGS ARE ENOUGH FOR NEGATING THE INCREASE IN NUCLEAR CHARGE..
HOPE THIS WILL HLP!

Answer 4

why doesnt it stay constnat as you go down as for each proton added, an electron is also added?

Answer 5

http://dl.clackamas.cc.or.us/ch104-06/efffective_nuclear_charge.htm
go to this link..........................

Answer 6

@Ravi2 "As you go down a group, the increase in the nuclear charge is balanced by an increase in the number of shielding electrons so that the effective nuclear charge remains the same." but thats not true? the effective nuclera charge decreases down a group ..

Answer 7

@ powerangers69.......as the no: of shells are increases down the group, that is why it is decreases....

Answer 8

Your reference (the UBC wiki) is wrong. Zeff tends to increase, not decrease, down a group, because the additional inner electrons are less than perfectly shielding. This effect is particularly enhanced once d and f electrons are part of the core, because they are more poorly shielding than s and p electrons, which explains, among other things, why the sizes of transition metal atoms hardly change as you go down the groups -- Zeff increases so much it pulls the extra shells inward, almost entirely cancelling the effect of another whole shell.

From WebElements.com, which in turn comes from SCF calculations by the famous Clementi, here are some Zeff trends going down a group:

In Group 2A: Be +1.91, Mg +3.31, Ca +4.40, Sr +6.07.

In Group 7A: F +5.10, Cl +6.12, Br +9.03, I +11.61.

Answer 9

hm if zeff increases down a group, shouldnt the nucleus attract the valence electrons stronger and cause the atomic radius to decrease? or does a radius increase due to energy levels

Answer 10

radius increases due to the electron-electron repulsion which shields electrons from the positively charged nucleus

Answer 11

@powerangers69, you are forgetting that with each row you get another whole shell of electrons. Yes, the increasing Zeff pulls EACH shell closer to the nucleus, but then you add another whole shell on top of that, too, which is further from the nucleus and feels even a large Zeff less (remember the Coulomb attraction falls off like distance squared). The net effect is usually a modest growth in radius, as the extra shell adds more than the increased Zeff takes away.