Ions in chemical compounds

[xami]

Hey =},

 

Im new to the forum so hi eveyone! Im studying the biology,chemistry and physics at college so i hope to learn a lot from here and also get some help please.

 

At the moment we're learning about ions and bonding, we've been given a peice of homework where we have to write down the resulting compound of two ions where the total charge will be zero..

 

Im really quite stuck with this so if anyone could help me out that would be cool.

 

one of them is: Na1+ and Cl1-

would this just end up as NaCl cause the + and - cancel each other out?

And if that is the right answer am i working it out rite?

 

Another one is NH4[math]^{1+}[/math] and NO3[math]^{1-}[/math]

 

Im really not sure how to do this one =/

 

If anyone could help me and explain a little that would be really helpful. Thanks!

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Merged post follows:

Consecutive posts merged

For the first question where there is the -1 and +1 thos are the small numbers that sit at the top right hand side of the element letter, not sure what that is called either =/? Just says about the charge after the element has gained or lost electrons right?

 

Its the same for the second question too.

 

Thanks!!

Edited October 22, 2009 by xami
Consecutive posts merged.

[Psycho]

The NaCl one is fine that is just common table salt.

 

NH4+ (if it is only a change of 1 you don't need the 1) and NO3- works exactly the same way.

 

Just as extra information the charge is based on the group of the element so group 1 have +1, group 2 have plus 2, but when you get the left hand side of the periodic table with 5 electrons they are 3- as it takes less energy to get 3 electrons from say 3 Na+ ions rather than lose 5.

 

So N has a charge of 3- and H has +1 so +4-3= +1 and the same idea for the nitrate ion (NO3-) but in that case as nitrogen is close to the middle of the periodic table (excluding the transition metals) Oxygen is more electronegative so is the negative ion whereas Nitrogen is less electronegative (therefore more positive) so works as the positive ion, this only occurs with ions in the centre of the group 5 elements commonly though.

[xami]

Okay, so then it would be like

NH4 1+ and NO3 1- ----> NHNO1 ?

 

Thanks for the help =), nt sure i really understand tho sorry

[aeontide]

The compound formed between NH4+ and NO3- is called Ammonium nitrate, it, like NaCl, will form a salt. The formula for this compound is (NH4)(NO3).

 

The bonding structure looks something like this, which you may find to be a somewhat similar configuration to what you come across in table salt, NaCl.

[xami]

They dont really look that similar to me =/ lol.

 

Ok.. so you got (NH4)(NO3) from NH4+ and NO3-.. What do the 3 and 4 mean? That for every 4 NH there is 3 NO? dont you have to add or subtract or times them together at all?

 

Also what would it be if it was NH4 1+ and SO4 2- (Ammonium sulfate)?

 

Thanks for your help =)

[Fuzzwood]

NH₄ means there are 4 hydrogens attached to that N. The whole thing is 1 single ion with +1 as a charge. Lets name that X⁺ for a while. Making ammonium sulphate with that would result in X₂SO₄. Replacing the X with ammonium: (NH₄)₂SO₄.

 

The () are needed to distinguish between 2 ammonium and NH₄₂. The latter obiously does not exist.

[xami]

Ok thanks, this is making some sense..

 

But where does the 2 after the NH bit come from?

[aeontide]

It means that there are 2 NH4 groups attached to, in this case, 1 SO4...

 

If you are referring to when they wrote NH42, then it is simply without the parentheses.

[hermanntrude]

ammonium and nitrate are examples of polyatomic ions.

 

A polyatomic ion is a group of atoms with a charge on them.

 

[ce]NH4+[/ce] means that there is a group of atoms containing one nitrogen atom, four hydrogen atoms, and having a charge of 1+

 

[ce]NO3-[/ce] means that there is a group of atoms with one nitrogen, three oxygens and a single negative charge.

 

here is a list of polyatomic ions with some explanation. Most chemistry courses require students to memorise the formula and charge of a few polyatomic ions. Check your notes to see if you've been provided with a list like that, or ask your instructor.

[xami]

This is making a lot more sense now, thanks for everyone who helped me with this.

 

The last thing is that i understand tht there are two NH attached to SO but why?

 

How do you work out tht you need 2 NH? why not 2 SO for example?

 

I know, im slow..

 

Thanks a lot! I really appreciate it.

 

edit: yeh our teacher did give us a big list of the polyatomic ions =)

Edited October 27, 2009 by xami

[Psycho]

This is making a lot more sense now, thanks for everyone who helped me with this.

 

The last thing is that i understand tht there are two NH attached to SO but why?

 

How do you work out tht you need 2 NH? why not 2 SO for example?

 

I know, im slow..

 

Thanks a lot! I really appreciate it.

 

edit: yeh our teacher did give us a big list of the polyatomic ions =)

It is just due to the net charge of the ions, NH4+ has a single net positive charge and NO3- has a single negative charge so to balance the charge you take one of each a -1+1= 0. SO4 2- has a net negative charge of -2 so it will take twice as many NH4+ ions to balance it -2+1+1= 0.

[Patty Raelyn]

How do i understand the charge of chemical compounds ions wether they are negative or positive?

[hermanntrude]

for monatomic ions (ions made of a single charged atom), metals are positive and non-metals are negative (nearly always... there are a few exceptions but they ignore them at you level of chemistry).

 

For polyatomic ions (things like [ce]NO3-[/ce] for instance which contain multiple covalently bonded atoms but only one charge) you'll have to memorise them. However if you only need to know whether they're negative or positive, negative is the best bet since there are only two commonly cited positive polyatomic ions ([ce]NH4+[/ce] and [ce]Hg2^2+[/ce]).