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Course: Chemistry library > Unit 1
Lesson 3: Names and formulas of ionic compoundsNaming ionic compound with polyvalent ion
Naming ionic compounds that contain polyvalent ions, using example of cobalt (III) sulfide.
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How do you know that cobalt is a "D block" element?(17 votes)
We have defined groups 3-12 on the periodic table as being the d block, and cobalt is in group 9.
They have anywhere from 1-10 d electrons as those are the orbitals being filled in that block from one element to the next.(32 votes)
Why are some elements polyvalent and others not?(15 votes)
Polyvalent elements are elements in the d-block(transition metals) and they can take on multiple charges to have either 2 or 8 valence electrons. Groups determine the charge (or electron on outermost shell). Transition metals have no group so their charges are undefined. Groups 1, 2, 13, 14, 15, 16 and 17 all have a defined number of valence electrons.
I really hope this helps.(15 votes)
How do we automatically know that the cobalt is a cation and the sulfur is an anion?(13 votes)
That is a good Question emmacwarenn , to find that first we need to know that two opposite ions get together and make a molecule. So in the periodic table you get S block and the P block, so you get numbers AI , AII , AIV etc.. up-to AVIII for them, (neglect D and F blocks for a moment)
now the elements in AI , AII , AIII columns like to give there electrons in the outer most shell and be +1 , +2 and +3
but AIV can be +4 or -4 and
then AV , AVI , AVII they want to fill their outer most shell and become -1, -2, -3
but AVIII is noble gases they are not reacting like any other elements in the whole periodic table so you don't have to worry about it at the beginning of Chemistry lessons.(14 votes)
- Are Polyvalent Ions found only in the Transition Metals? Can any of the other groups have them as well? If not, why? If so, like what?(5 votes)
- Not just transition metals, lead and tin for example both form +2 and +4 ions.(11 votes)
Could the answer also be Cobalt (III) Sulfite instead of Cobalt (III) Sulfide?(1 vote)- No because sulfide and sulfite are two different things.
Sulfide is the negative ion of sulfur, S^2-
Sulfite is a polyatomic ion with the formula SO3^2-(14 votes)
Does this make sense?
To find the charge of each element, we need to look at the periodic table. Li when bonded with Oxygen, would have a charge of 1+. (Li1++)2 and Oxygen would have a charge of 2-. (O2-). We now need to find the neutral version of this formula. We can use the criss cross method to figure out how many of each element is in this compound.
If Li has a charge of 1 and Oxygen has a charge of -2 the formula would be Li2O.
Another Question: Is the name Lithium oxide or Lithium 1 oxide?(6 votes)
The statement is correct. In order to cancel out the -2 charge on the oxygen, we need 2 lithium ions, because each lithium ion has a +1 charge. (1 + 1 - 2 = 0) All ionic compounds are neutral.
In your second question, the name of this compound would belithium oxide. Roman numerals are only used to represent the charge on an ion when you are dealing with an element that has multiple oxidation states (forms cations of different charges), such as iron.(4 votes)
How do we determine the charge of molecules like SO4? In unit test it says that the charge of SO4 is 2-, but I can't get to that number myself. Can anyone explain the process of determining the charge of similar molecules?(4 votes)- You can’t. You need to memorise the charge of polyatomic ions along with their formula because there’s pretty much no way to derive them.(3 votes)
- How do you know that the sulfur would want to gain 2 electrons for a complete outer shell?(3 votes)
- Sulfur is in group 16 which means it has 6 valence electrons. 8 is a full shell...so it needs 2 more.(3 votes)
- What's with the Uus Uuo and abbreviations like that? Aren't those Tennessine and Oganesson?(2 votes)
- The other replier is mostly correct, but I wanted to add some extra information.
The symbols like Uus and Uuo for Ununseptium and Ununoctium respectively are known as systematic element names which are placeholder names for elements yet to be successfully synthesized and verified. The system was adopted by the IUPAC in 1978 to avoid ambiguity or controversy about referring to the undiscovered elements. At the time of adoption only the elements up to atomic number 103 were discovered and named with nonsystematic names. The remaining undiscovered elements were given these systematic names which could be used to designate elements 100 – 999 (three digit numbers). Once an element is discovered and its discovery is verified, a new unique name is given to it and the systematic name is discarded.
The actual system uses a combination Greek and Latin numbers to make a three-digit number. Each element receives a “-ium” suffix. So a name like Ununseptium uses the latin “Un” for one and “Sept” for seven. It translates to element 117, Un(1)un(1)sept(7)ium. The symbol is simply the first letter of each number, Uus. Ununoctium use the Latin “Un” again, but also the Greek “Oct” for eight. So it translates to element 118, Un(1)un(1)oct(8)ium, and it’s symbol is Uuo.
Hope that helps.(2 votes)
What is d block? Is it another name for transition metals? So in conclusion,only transition metals can take on multiple charges right?(2 votes)- a "d" block element is an element were the d orbitals are the main orbitals and they or their ions have partially filled d orbitals.
Metals generally form positively charged cations with a +2 charge. Transition metals can form more than one kind of cation. Halogens form an anion with a single negative charge. Group 16 elements generally form anions with 2 negative charges, while group 15 elements often form -3 charge anions. In conclusion, the d block is a descriptive name for the transition metals. but transition metals are not the only ones who can take multiple charges. hope that helps.(2 votes)
Video transcript
- [Instructor] So we have the
formula for an ionic compound here, and the goal of this video is what do we call this thing? It clearly involves some
cobalt and some sulfur, but how do we name it? Well, the convention is, is
the first element to be listed is going to be our cation,
and if we look at cobalt over here, we see that
it is a D-block element and D-block elements are
tricky because you don't know exactly how it will ionize. So we know that this is
going to be our cation, it's going to be our positive
ion, but we don't know what the charge on each of those cobalt is actually going to be. So now let's look at the anion,
let's look at the sulfur, or as an anion, the sulfide. So let me underline that. And on the periodic table,
we see sulfur is out here that in its group, it would
want to gain two electrons in order to have a complete outer shell. It's just like oxygen, it
wants to gain two electrons. So the sulfide anion will look like this. So it will have sulfur when it ionizes will have a two minus
charge, just like oxygen, just like everything else in this group. It would want to gain
one, two electrons so that its outer shell looks
like that of a noble gas, looks like that of argon. We can use this as a clue
to figure out what must be the charge on the cobalts because we have three of the sulfides. Each of the sulfides
has a two minus charge, and we have three of them,
so that's going to give us a six minus charge all in. And then the cobalt, we have two of them. And so these two cobalt have to offset this six minus charge. They have to have a six plus charge. Well that means that each of them need to have a three plus charge. If each of these have a three
plus charge and you have two of them, then you're gonna
have six plus on the positive side and you're gonna have
six minus from the sulfides. And the reason why this is useful for us is now we can name this. We would call this ionic compound Cobalt III, cobalt and you would write it with Roman numerals
here, Cobalt III Sulfide, Cobalt III Sulfide. Now I know what you might be thinking. Hey, when we looked at
other ionic compounds, I didn't have to write the
charge of the cation there and the reason why the
convention is to do it here, and I don't have to write in upper case there, so let me rewrite it as cobalt (III) sufide. The reason why I wrote
that three in this case is because the cobalt can
take on multiple charges. It's known as polyvalent, polyvalent. If something is in group one,
you know it tends to have a positive one charge. Group two tends to have
a positive two charge. If it's a halide, it tends to
have a negative one charge. But these metals here
in this D-block here, they could be ionized in multiple ways. And so that's why we have to
figure out what the charge of the cobalt is, and we
write it here in the name. We would call this cobalt (III) sulfide. You could have other ionizations
of cobalt in other ionic compounds, but this one
is cobalt (III) sulfide. And you could go either way. You could say, okay if the
cobalt has a charge of three plus you could figure out its
formula right over here, or as we just did in
this video, you could go from the formula to the actual name.