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Offline Guillem_dlc

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Nuclear charge of an anion
« on: April 24, 2018, 10:27:41 AM »
THE PROBLEM STATEMENT:

A triply charged anion is isobaric with Zn6530 and isotonic with an X atom that has a mass number of 70 and whose penultimate electron has the following quantum numbers (n=4; l=0; m=0; s=-1/2). Determine and mark the alternative with the correct nuclear charge of the initial anion.

a) 23.       b) 24.       c)25.       d) 26.       e) 27.

THE ATTEMPT AT A SOLUTION:

The problem is to find the nuclear charge (the number of protons) of an incognito anion.

I will call this unknown anion "Y". The statement says "a triply charged anion" that is, Y3-, it is isóbaro (not isobaric) with Zn6530, it means that they share the same mass number.

Then, between 65 and 30, the mass number must be the higher value because A = Z + ºn (mass number is the sum of the number of protons plus the number of neutrons). We have the mass number of the anion in question: Ay = 65.

On the other hand, it tells me that it is both isotonic, (that is not isotonic), with an atom "X" that has a mass number of 70 and whose penultimate electron has the quantum numbers (4,0,0, -1 / 2).

That is to say that: Ax = 70.

Then I focus on the data of that penultimate electron: n = 4 (this electron would be in level 4), l = 0 means that we would be in sub-level s. Also m = 0 and s = -1 / 2, then we are in exponent 2. All this leads me to conclude that the electronic configuration must end in 4s2.

Completing the configuration: 1s2, 2s2, 2p6, 3s2, 3p6, 4s2. Add the exponents and reach 20 electrons. But this data belongs to the penultimate electron, then the number that interests me is an atom with 21 electrons. As it must be neutral Zx = 21.

Ax=Zx+ºnx

70=21+ºnx

then ºnx=49. That is to say that I have the number of neutrons of the atom "X", which at his view were the same as for the anion "Y" (it was isotonic):

ºny=49

I can already ask the same equation for the anion in question:

Ay=Zy+ºny

65=Zy+49

Zy=16

That answer is not among the options. Can you help me?

Thanks

Offline Borek

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Re: Nuclear charge of an anion
« Reply #1 on: April 24, 2018, 11:18:31 AM »
Completing the configuration: 1s2, 2s2, 2p6, 3s2, 3p6, 4s2

What about filling 3d? 4s electrons can move to 3d and back to 4s.

Isobaric is intended to mean "same baryon number", that is, same A.

I suppose "isotonic" is intended to mean "isoelectronic" - having the same number of electrons.
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Offline Guillem_dlc

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Re: Nuclear charge of an anion
« Reply #2 on: April 24, 2018, 12:48:30 PM »
Thanks! I understand that these terms mean:

Isobar = same mass number

isotone = same number of neutrons

isoelectronic = same number of electronic

isotope = same number of protons (atomic).

What to fill the 3d sub-level, I was watching the electronic configuration of calcium and ends up filling with the level 4s2. And for the scandium that has 21 electrons, we only get to sub-level 3d1.

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