[confusedstud]

There are some atoms and ions given with particularly 3 atoms and ions which makes me confused.
S: 10 electrons 12 protons 12 neutrons
U: 10 electrons 7 potons 14 neutrons
R: 12 electrons 12 protons 12 neutrons
which two particles combine together to form a compound with a chemical formula of X2Y3.

So in this case, X would be U3- and Y is S/R2+. However, which one do i use S and U or R and U? Since in the S and U case it would simply be: S2+ + U3-  :rarrow:S3U2

However, the other reaction is also feasible since R is a metal and U3- will exist in a solution form. So by 'combining them' I would also get S3U2 or R3U2. So is this correct too?

In this case i feel the first example would be the better answer. But is anything wrong with the second one? Because that reaction can also take place. What would be the guideline to follow for these types of questions?

[Dan]

Firstly:

U: 10 electrons 7 potons 14 neutrons

²¹N^3-! Really?

So in this case, X would be U3- and Y is S/R2+. However, which one do i use S and U or R and U? Since in the S and U case it would simply be: S2+ + U3-  :rarrow:S3U2

You do not have R²⁺ as an option. You have: R, a neutral atom (¹²Mg), and two ions, S and U. What are the charges of S and U?

U = X^3-
? = Y²⁺

[confusedstud]

Firstly:

U: 10 electrons 7 potons 14 neutrons

²¹N^3-! Really?

So in this case, X would be U3- and Y is S/R2+. However, which one do i use S and U or R and U? Since in the S and U case it would simply be: S2+ + U3-  :rarrow:S3U2

You do not have R²⁺ as an option. You have: R, a neutral atom (¹²Mg), and two ions, S and U. What are the charges of S and U?

U = X^3-
? = Y²⁺

S=Y²⁺

But they can still react right? Because when S and U ions react, they have to have their own respective anion or cations so should the other reaction be feasible as well? For example, something like this could happen 3R+2UZ :rarrow:U2R3+2Z

[Dan]

S=Y²⁺

I agree

Because when S and U ions react, they have to have their own respective anion or cations so should the other reaction be feasible as well?

I can't follow your logic - I don't understand what you mean.

For example, something like this could happen 3R+2UZ :rarrow:U2R3+2Z

We know U has a charge of 3-, so in this equation Z must have a charge of 3+. We know R is neutral.

Consequently, U₂R₃ is an anion a charge of 6-. It will (a) not be stable, and (b) is an ion, not a compound.

The question you originally posted asked which particles can be combined to give a compound. Compounds are charge neutral by definition. An ion can be part of a compound, but an ion cannot exist by its self in pure form.

[confusedstud]

Sorry but I don't quite understand what you mean. Because isn't S just these ion of R? So can't the actually atom of R react with U as well? Like for example sodium hydroxide can react with an acid, but so can sodium to form the same salt. Thanks :-)

[Dan]

OK, we will look at your example:

Na⁺ + ^-OH + H⁺ + Cl^-  Na⁺ + H₂O + Cl^-

Now, if we just swap Na⁺ and ^-OH with Na as you suggest:

Na + H⁺ + Cl^-  Na⁺ + H₂ + Cl^-

The products are different - the same salt is formed, but in the first case we form water and in the second hydrogen. You cannot just replace sodium salts with sodium metal and get the same reaction.

Again for this question:

Your particles are: Mg²⁺, Mg, and N^3-

Particle combinations in a 3:2 ratio are:

3Mg²⁺ + 2Mg  Mg₅⁶⁺ <- an ion that does not exist
3Mg²⁺ + 2N^3-  Mg₃N₂ <- a neutral known compound
3Mg + 2Mg²⁺  Mg₅⁴⁺ <- an ion that does not exist
3Mg + 2N^3-  Mg₃N₂^6- <- an ion that does not exist
3N^3- + 2Mg  Mg₂N₃^9- <- an ion that does not exist
3N^3- + 2Mg²⁺  Mg₂N₃^5- <- an ion that does not exist

The only sensible answer is the second one.

[confusedstud]

But in the question, they said that which two particles chemically combine to form a compound with the chemical formula X2Y3. So R+ZU R3U2+Z. isn't this reaction feasible? The first one would be S2+ +U3- S3U2 so what's wrong. Aren't R and S just atoms and ions respectively? They are still capable of chemically combining to form the sane product right? What am I seeing wrongly? Thanks Dan!

[Dan]

Aren't R and S just atoms and ions respectively?

Yes

They are still capable of chemically combining to form the sane product right?

No.

R = Mg
S = Mg²⁺
U = N^3-

So:

3S + 2U  S₃U₂ is the same as 3Mg²⁺ + 2N^3-  Mg₃N₂

and

3R + 2U  R₃U₂ is the same as 3Mg + 2N^3-  Mg₃N₂^6-

These two sets of equations are not the same. The second reaction is not chemically feasible.

[confusedstud]

Oh i think i understand i was thinking that it could be like Mg+H₂N₃ :rarrow:Mg₃N₂ +N2 or something like that such that the cations are balanced in the reaction. So is it right for me to say that when i approach such questions i literally take the two of the particles and add them together (no other stuff to balance the charges and so on)?

Thanks so much Dan!

[Dan]

So is it right for me to say that when i approach such questions i literally take the two of the particles and add them together (no other stuff to balance the charges and so on)?

Yes, that is what the question asked in this case

Thanks so much Dan!

No problem