Question

What is the identity of the element X in the following ions?

(a) X2+, a cation that has 38 electrons

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(b) X -, an anion that has 18 electrons

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Answer 1

You know that the NEUTRAL element has a number of electrons EQUAL to `Z`...

Explanation:

And `Z_"the atomic number"` unequivocally characterizes the element, and gives the number of positively charged massive particles that are present in the nucular core. Do you follow...this is simply a consequence of simple electrostatics...

We gots...`X^(2+)` with 38 electrons. Neutral `X` NECESSARILY contains 40 electrons, and THUS ALSO 40 nucular protons, i.e. `Z=40`... And a quick glance at the Periodic Table shows that if `Z=40` we gots zirconium.

And we also got `X^-` with 18 electrons. The parent atom necessarily has 17 electrons, and thus `Z=17`...and if `Z=17` we gots the element chlorine.

This is something fundamental to understand, and it underlies our understanding of matter. And so if there are queries or something you want clarified, raise the objection and someone will help you.

Note that there should be a copy of the Periodic Table beside you now.... You cannot be expected to learn the Periodic Table at an elementary stage, and you will always be procided with a copy of the Table in your chemistry and phyzicks exams....