Effective Nuclear Charge, Atomic Size, and Ionization Energy

Today in class Mrs Mandarino first stamped our homework, which was #9 on the metal reactivity lab and pages 4-5 on effective nuclear charge. After that, we went over effective nuclear charge.

When protons increase --> greater pull on electrons, so its a smaller radius

We also learned how to find shielding electrons. The overall postivite charge that the electron gets is the effective nuclear charge (Z*). to find it, we can use a mathematical expression:

Z*=Z-S Z*- the effective nuclear charge
Z-the number of protons in the nucleus
S- the shielding electrons (electrons between the outer electron and nucleus)


Then we checked page 5. For 1, we had to find the number of shieling electrons. To do this, you cross out the highest energy level.

Example: Al 1s2 2s2 2p6 3s2 3p1
Cross out the third energy level because it is the highest and therefore the outer or valence electrons. Then you count the other electrons to get an answer of 10 sheidling electrons.

Part 2 was to find the effective nuclear charge. To do this, we had to use the mathematical expression.

Example: Al- Z*=13-10=3
13 is the number of protons in the element Al and 10 is the number of sheilding electrons. The answer 3 means that there are "3 protons pulling on the electrons"

Next, we learned about Atomic Size. We figured out that when you move down a column, the effective nuclear charge (Z*) stays the same. When you go across a row, (Z*) goes up. So the pull is stronger to the nucleus. More energy levels make the size of the atom larger, and a higher effective nuclear charge will make the size of the atom smaller.

Then we talked about Ionization Energy. This is the energy that can get the electron to completely leave the atom. So, the greater the force is that holds the electron in place, the more energy it will take to remove the electron.

When you move down a column, (Z*) stays the same, and the atomic size increases because there are more energy levels. So the ionization energy will decrease because the outer electrons are further from the nucleus. As you move across a row, ionization energy will increase because there is a stronger pull from the nucleus.

The homework for tonight was to do pages 10 and 11 and work on the webassigns!