[JonathanEyoon]

Just started nomenclatures and so far we've covered naming
 
1. Binary Compounds (metal and nonmetal?)
2. Naming Compounds where the cation can have more than one charge which is written in Roman Numeral?
3. Naming two nonmetal element compounds
4. Naming Acids
5. Naming Acids with Oxygen


Well I'm having the hardest time understanding how the formulas are written  and how to understand it.  I have a major test on Tuesday  and I need to get this stuff down cold.

Starting with Binary Compounds, will the suffix always end in "-ide"? I know HOW to write the Binary Compounds to a certain degree but I don't understand why  .  For instance

Mg 2+ and N 3-.  The way the professor told us to write this is simply by criss crossing the ion charges where they will become each others subscript.  So it'll be Mg3N2.  I get how to do it but why? 

[Kryolith]

Have a look at

http://en.wikipedia.org/wiki/IUPAC_nomenclature_of_inorganic_chemistry

Mg 2+ and N 3-.  The way the professor told us to write this is simply by criss crossing the ion charges where they will become each others subscript.  So it'll be Mg3N2.  I get how to do it but why? 

Mg is in the 2nd main group it "wants" to donate 2 electrons to gain an electron octet.
N is in the 5th main group it "wants" to accept 3 electrons to gain an electron octet.

3xMg donate 6 electrons and 2xN accept 6 electrons. ===> Mg₃N₂ (magnesium nitride)

Do not hesitate to ask more questions...

[JonathanEyoon]

What's an octet?

Where did the 3 x Mg and 2 x N come from?  Sorry i'm so horrible at this 

[Kryolith]

electron octet = 8 valence electrons (noble gas electron configuration)
Maybe the word is uncommon in English, I'm sorry.

Where did the 3 x Mg and 2 x N come from?  Sorry i'm so horrible at this 

At least you are interested to understand it and don't want to do it without knowing why. That's a good attitude.

We know both atoms "want" 8 electrons and we figured out that 1 N-atom has to accept 3 electrons and 1 Mg-atom has to donate 2 electrons to reach this state right? The least common multiple of 2 and 3 is 6, thus you know that 6 electrons are being transferred.
1 Mg donates 2 ---> you need 3xMg
1 N accepts 3 ----> you need 2xN

I hope you got it 

[JonathanEyoon]

Ohhhh I think I understand it to a certain degree now.


Since what we want is a neutral compound without any ion charges we would have to find how many of each element we need to cancel out the ion charges.  And to do this, we find a common multiple of the ion charges.

So since Mg has a +2 and Nitrogen has a -3, it'll take 3 Magnesiums and 2 Nitrogens to cancel out the charges so it'll be neutral which would create Mg3N2

Ok I think I get that part now 

So another example would be using Potassium and Sulfur.  Since K has a cation of 1 and Sulfur has a anion of 2, it'll take 2 K atoms to neutralize the charges where we have a zero charge thus forming a binary compound right?

Ok next question would be how to determine the charges for Transition metals and nonmetals.  Example : Copper and Sulfur?  I remember hearing the professor say we have to make use of roman numerals.  Also which are cations and which are anions in the periodic table? Would Transition metals be cations?

[Borek]

K₂S it is, right you are

In general metals are always cations. As to transition metals... At this stage you better simply try to remember some most popular. Copper can be 2+ or 1+, much more often 2+. Roman numerals are used to denote valence/charge once you know it. So you have two binary compounds of copper and chloride - Cu(II)Cl₂ and Cu(I)Cl (as the Cl^- charge is always -1 it is obvious wheteher copper is I or II when you have the formula, thus you will rarely see roman numerals used this way; but they should be used whenever things are not clear).

[Kryolith]

some important cations:
Zn²⁺, Fe²⁺, Fe³⁺, Ni²⁺, Ag⁺, Cu²⁺, Cu⁺, Ti⁴⁺, Co²⁺, Co³⁺

[JonathanEyoon]

Ok with the whole roman numerals,

The professor told us the cation of the transition metal will depend on what the nonmetal is.  I don't know if that's right or wrong but I do know I had no idea what she was talkinga bout  .  For instance

FeCl3

What you just told me was that Fe has two states where it's +3 and +2.  How do you determine which one it is just by looking at FeCl3?

[JonathanEyoon]

wait I think I just answered my own question.  It's Iron(III) because Cl has 3 atoms right?

Cl has 1 anion so that would mean since Fe has one atom and Cl has 3 atoms, Fe MUST have 3 cations.

Fe +3 and Cl -1  . So this means I would need 3 Cl atoms to make

FeCl3 which is pretty clear that it's Iron(III) Amirite!?

[Borek]

FeCl3 which is pretty clear that it's Iron(III) Amirite!?

Perfect

There is also another iron chloride, with the FeCl₂ formula. What valence/charge does iron have in this compound?

You should see now why "iron chloride" is ambiguous, while "iron (III) chloride" is not.

[JonathanEyoon]

So FeCl2 will be

Iron(II)Chloride.  It's Iron(II) because I would need 2 chloride atoms to make the compound neutral because Iron would have a +2 cation.  Ok I think i'm starting to get this little by little. It's starting to all click  .


Question, Do all transition metals have varied cations?

[Kryolith]

Great job!   

Question, Do all transition metals have varied cations?

Yes. Every transition metal can occur in a different oxidation state. Some of the oxidation states are more frequent than others, depending on the metal.

EDIT
misspelling corrected

[JonathanEyoon]

So if I were to be asked to write the formulas for these

potassium sulfide
calcium chloride
lead (II) nitrate
silver sulfide
magnesium sulfate

It would be

K2S for Potassium Sulfide
CaCl2 for Calcium Chloride
Pb(NO3)2 for lead(II)nitrate

I'm lost with the silver sulfide

MgSO4 for Magnesium Sulfate

Did I get them right? Can you help me with Silver Sulfide. Does silver have varied cation charges as well?

[Kryolith]

100% correct!

some important cations:
Zn²⁺, Fe²⁺, Fe³⁺, Ni²⁺, Ag⁺, Cu²⁺, Cu⁺, Ti⁴⁺, Co²⁺, Co³⁺

I am sure you can tell the formula of silver sulfide.

[JonathanEyoon]

Silver Sulfide is Ag2S?

Is there a website I could go to where I could practice these and it could tell me whether i'm right or wrong?