# Quick "effecive nuclear charge" question

##### Still in California
Moderator
15+ Year Member
Maybe one of you genius-types can clear this up for me. I'm reading conflicting information between texts I'm using.

What is the trend on the periodic table for effective nuclear charge? Examkrackers says that it increases going left to right and top to bottom.

Left to right is logical (more electrons in same shell, so no further electron sheilding plus more protons for attraction) but the top to bottom part is counter intuitive.

When you go down a period, you're also adding a new shell, so the electrons are further away and there is more sheilding effect. I realize you have slightly more protons, but that couldn't offset it. Is this a typo in Examkrackers?

#### doublehh03

##### Senior Member
10+ Year Member
Maybe one of you genius-types can clear this up for me. I'm reading conflicting information between texts I'm using.

What is the trend on the periodic table for effective nuclear charge? Examkrackers says that it increases going left to right and top to bottom.

Left to right is logical (more electrons in same shell, so no further electron sheilding plus more protons for attraction) but the top to bottom part is counter intuitive.

When you go down a period, you're also adding a new shell, so the electrons are further away and there is more sheilding effect. I realize you have slightly more protons, but that couldn't offset it. Is this a typo in Examkrackers?
i think it increases across a period (so that's right) but DECREASES down a group b/c like u said, e- are then starting to fill up the d and f orbitals

#### Condeeleza Rice

##### Junior Member
10+ Year Member
it increases from top to bottom but coloumbs law takes over from top to bottom. Remember F=kq1q2/r^2

#### Polodog21

##### Junior Member
10+ Year Member
doublehh03 said:
i think it increases across a period (so that's right) but DECREASES down a group b/c like u said, e- are then starting to fill up the d and f orbitals
double is right!

OP

Moderator
15+ Year Member

#### QofQuimica

##### Seriously, dude, I think you're overreacting....
Staff member
10+ Year Member
Thanks, all!
I wrote a post about this in the gen chem explanations thread in the MCAT subforum that you may want to talke a look at.

OP

##### Still in California
Moderator
15+ Year Member
Thanks, Q. Are we not in the MCAT subforum? Do you have a thread title, by any chance?

Staff member