Due to the screening effect, the 3s electrons of magnesium (Mg) feel an effective nuclear charge (Zeff) of:

1. +1
2. +2
3. −2
4. +12
5. +4

To determine the effective nuclear charge (Zeff) felt by the 3s electrons of magnesium (Mg), we need to consider the concept of screening or shielding effect.

The shielding or screening effect is the reduction in the attractive force between the positively charged nucleus and the outermost electrons due to the presence of inner electrons. Electrons in inner energy levels partially shield or screen the outer electrons from the full nuclear charge.

In the case of magnesium (Mg), the atomic number is 12, which indicates that there are 12 protons in the nucleus. The 3s electrons are located in the third energy level.

Now, to determine the effective nuclear charge (Zeff) felt by the 3s electrons, we need to consider the shielding or screening effect of the inner electrons.

In magnesium (Mg), the first two energy levels (1s and 2s) are filled with electrons. These inner electrons create a screening effect by shielding the 3s electrons from the full nuclear charge.

Since the 3s electrons are shielded by the inner electrons, they do not experience the full charge of the 12 protons in the nucleus. The effective nuclear charge (Zeff) felt by the 3s electrons is less than the total number of protons.

Considering this, the correct answer is option 2: +2. The 3s electrons in magnesium (Mg) feel an effective nuclear charge (Zeff) of +2 due to the screening effect of the inner electrons.

nuclear charge = +2

Mg has a nuclear charge of +2.

I couldn’t understand please explain this again

Hmm, let me think about this. Ah, I got it! It's like the 3s electrons of magnesium are at a fancy party, but there's a bunch of people in between them and the host, which is the nucleus. So, because of the screening effect, the effective nuclear charge they feel is like trying to get the host's attention through a crowd. And the answer is... drumroll, please... Number 2! +2 is the correct answer. Way to go, magnesium's 3s electrons!

nuclear charge = +12

1s, 2s, & 2p electrons = 10
+12-10 = 2 for the effective nuclear charge on the two 3s outside electrons