[meeztered]

There doesn't seem to be much information on the internet about this, and my chem teacher won't really help me out. It's due tommorow, even if someone can't respond before then I would still like to know the answer sometime. here it is:

Atoms and ions with the same number of electrons are called iso-electronic. Write a symbol for a cation and an anion that are iso-electronic with krypton. Is it possible for a cation to be iso-electronic with an anion from the same period? Explain.

If someone could give me a hint or anything that would be cool. thx.

[enahs]

O^2-, F^-, Na⁺ and Mg²⁺.
They are all have the same number of electrons (10), but different number of protons (8,9,11,12).
They are all isoelectronic ions. You should be able to figure out which noble gas they are isoelectronic with and go from there to answer your question.

[meeztered]

ok so Mg²⁺ is isoelectronic with Ne right? So if thats right then Se^2- and Sr²⁺ would be isoelectronic with Kr right?

[enahs]

Yes, but make sure you understand what the subscripts 2+ and 2- mean. Just do not follow the same pattern I did because it is a pattern. Make sure you are following the pattern because you understand what the subscript mean, and what Mg2+ means, etc.

[meeztered]

Yea I know what it means, ^2- is adding 2 electrons and ²⁺ is taking away 2 electrons, and Se^2- is isoelectronic with krypton because they would have the same number of electrons.

And for the second part of the question, "Is it possible for a cation to be isoelectronic with an anion from the same period?", It would be possible right? Because wouldn't Al^- be isoelectronic with P⁺

[enahs]

And for the second part of the question, "Is it possible for a cation to be isoelectronic with an anion from the same period?", It would be possible right? Because wouldn't Al- be isoelectronic with P+

This is a tough question, not because it is hard but because the answer is based on what you are taught. Chemistry is typically slowly built up on semi-right and wrong principles.

So for the example you have given, based on the periodic trends you have learned from your teacher and in your book, is it possible for Aluminum to form a cation and phosphorus to from an anion?