Can you explain what the pseudo-gas configuration is? I have the definition but I still don't understand.

I have the example..
Sn([Kr] 5s24d105p2) Sn4+ ([Kr]4d10)+4e-

I understand the first part but I don't understand the second.

Let's take a couple that are easier to write to give examples. Na and Zn.

11Na is 1s2 2s2 2p6 3s1. It loses the one valence electron (the 3s) to become 1s2 2s2 2p6 = 10 e and that is Ne. That is the Na +1 ion is isoelectronic with Ne and it has a filled outside shell. Thus Na atom has become a Na +1 ion that looks like Ne and this is a noble gas so we say Na has attained a noble gas configuration.

30Zn is 1s2 2s2 2p6 3s2 3p6 3d10 4s2. Zn loses the two outside valence electrons to become
1s2 2s2 2p6 3s2 3p6 3d10 = 28 electrons. Notice that the Zn +2 ion has all filled shells BUT 28 is not a noble gas. So we call that a psuedo noble gas (it has filled shells as a noble gas does; however, it isn't a noble gas). Now apply that to your problems. You see the element Sn loses the 5s2 and 5p2 (the four outside valence electrons) for a +4 ion but it is a pseudo noble gas (because the 4d shell is filled BUT it isn't a noble gas). Count up the electrons. It would need to have either 54 or 36 to be a noble gas configuration.

Certainly! The pseudo-gas configuration refers to the electron configuration of an element or ion in which the outermost energy level is represented as a noble gas configuration. This is done to simplify the electron configuration notation by showing only the valence electrons.

In your example, the first part "[Kr] 5s^2 4d^10 5p^2" represents the electron configuration of the neutral tin atom (Sn) before it loses electrons. The [Kr] indicates that the first 36 electrons of tin fill up the same orbitals as the noble gas krypton.

The second part "Sn^4+ ([Kr] 4d^10) + 4e^-" represents the pseudo-gas configuration of the Sn4+ ion. The superscript 4+ indicates that it has lost four electrons from the neutral Sn atom. Note that the electron configuration for the Sn4+ ion only shows the electron configuration for the valence electrons, skipping the filled inner orbitals.

To understand the second part better, let's break it down step by step:
- "Sn^4+" indicates that it is the tin ion with a charge of 4+.
- "([Kr] 4d^10)" represents the electron configuration of the noble gas krypton, which has 36 electrons.
- "+4e^-" indicates that the Sn4+ ion has gained four extra positive charges by losing four electrons when compared to the neutral tin atom.

By using the pseudo-gas configuration, we can simplify and represent the electron configuration of ions without explicitly writing the configuration of all the inner electrons.