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Memorizing polyatomic ions? Using Periodic Table
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Martin David McCoy
Memorizing polyatomic ions? Using Periodic Table
This is about the charges of polyatomic ions, determined by the number of valence electrons (i.e. group number in the periodic table) brought by all the atoms in the ion:
If the polyatomic ion contains an odd number of atoms from elements with odd atomic number the charge of the polyatomic ion is odd.
Otherwise the charge is even. The most common charges for anions are -1 and -2, and for cations +1 and +2.
This is about the charges of polyatomic ions, determined by the number of valence electrons (i.e. group number in the periodic table) brought by all the atoms in the ion:
If the polyatomic ion contains an odd number of atoms from elements with odd atomic number the charge of the polyatomic ion is odd.
Otherwise the charge is even. The most common charges for anions are -1 and -2, and for cations +1 and +2.
@KarstenTheis Thanks for copying the rule over here. The only exceptions should be (unstable; reactive) radical ions with an odd number of electrons.More
All other -ate elemental anions will have four oxygens.
(Take note of ‘aluminate’ which I haven’t physically seen in that form yet but your teacher seems to insist be $\ce{AlO2-}$; disregarding this general trend.)
From the -ate anion, remove one oxygen to arrive at the -ite, remove two for hypo-ite. Add one for per-ate.
Charge:
Start at an anion with the most oxygens. (Note: Usually this is the -ate but because the halogens and permanganate are special they have the per-ate anion which is more oxygen-rich and important here.) Assume the maximum possible oxidation state for the non-oxygen atom. Assume $-\mathrm{II}$ oxidation state for every oxygen. Add up and take the negative value to arrive at the charge.
A hydrogen- will add $\ce{H}$ and lower the charge by one.
A thio- means one oxygen is replaced by sulphur.
A di- means take two of the (hydrogenated) anion and subtract water.Pyro means the same thing.
Memorise all the remaining! That is most importantly:
Chromite. Similar to aluminate I’ not sure if I ever saw it out in the real world.
Cyanide/cyanate. Thiocyanate is just like thiosulphate.
Oxalate, acetate and tartrate. Organic ions that will never fit into this scheme nicely.
Peroxide and superoxide. But those are -ides anyway.
Permanganate; which is almost like a perhalogenate. Luckily, molybdate and chromate fall into a category described above.
All other -ate elemental anions will have four oxygens.
(Take note of ‘aluminate’ which I haven’t physically seen in that form yet but your teacher seems to insist be $\ce{AlO2-}$; disregarding this general trend.)
From the -ate anion, remove one oxygen to arrive at the -ite, remove two for hypo-ite. Add one for per-ate.
Charge:
Start at an anion with the most oxygens. (Note: Usually this is the -ate but because the halogens and permanganate are special they have the per-ate anion which is more oxygen-rich and important here.) Assume the maximum possible oxidation state for the non-oxygen atom. Assume $-\mathrm{II}$ oxidation state for every oxygen. Add up and take the negative value to arrive at the charge.
A hydrogen- will add $\ce{H}$ and lower the charge by one.
A thio- means one oxygen is replaced by sulphur.
A di- means take two of the (hydrogenated) anion and subtract water.Pyro means the same thing.
Memorise all the remaining! That is most importantly:
Chromite. Similar to aluminate I’ not sure if I ever saw it out in the real world.
Cyanide/cyanate. Thiocyanate is just like thiosulphate.
Oxalate, acetate and tartrate. Organic ions that will never fit into this scheme nicely.
Peroxide and superoxide. But those are -ides anyway.
Permanganate; which is almost like a perhalogenate. Luckily, molybdate and chromate fall into a category described above.
This is about the charges of polyatomic ions, determined by the number of valence electrons (i.e. group number in the periodic table) brought by all the atoms in the ion:
Otherwise the charge is even. The most common charges for anions are -1 and -2, and for cations +1 and +2.
https://www.papazyan.org/oddoddodd_rule_for_polyatomic.html
This is about the charges of polyatomic ions, determined by the number of valence electrons (i.e. group number in the periodic table) brought by all the atoms in the ion:
Otherwise the charge is even. The most common charges for anions are -1 and -2, and for cations +1 and +2.
https://www.papazyan.org/oddoddodd_rule_for_polyatomic.html
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Number of oxygens:
If your anion is in:
then the -ate anion will have three oxygens.
All other -ate elemental anions will have four oxygens.
(Take note of ‘aluminate’ which I haven’t physically seen in that form yet but your teacher seems to insist be $\ce{AlO2-}$; disregarding this general trend.)
From the -ate anion, remove one oxygen to arrive at the -ite, remove two for hypo-ite. Add one for per-ate.
Charge:
Start at an anion with the most oxygens. (Note: Usually this is the -ate but because the halogens and permanganate are special they have the per-ate anion which is more oxygen-rich and important here.) Assume the maximum possible oxidation state for the non-oxygen atom. Assume $-\mathrm{II}$ oxidation state for every oxygen. Add up and take the negative value to arrive at the charge.
A hydrogen- will add $\ce{H}$ and lower the charge by one.
A thio- means one oxygen is replaced by sulphur.
A di- means take two of the (hydrogenated) anion and subtract water. Pyro means the same thing.
Memorise all the remaining! That is most importantly:
Periodic Table
Number of oxygens:
If your anion is in:
then the -ate anion will have three oxygens.
All other -ate elemental anions will have four oxygens.
(Take note of ‘aluminate’ which I haven’t physically seen in that form yet but your teacher seems to insist be $\ce{AlO2-}$; disregarding this general trend.)
From the -ate anion, remove one oxygen to arrive at the -ite, remove two for hypo-ite. Add one for per-ate.
Charge:
Start at an anion with the most oxygens. (Note: Usually this is the -ate but because the halogens and permanganate are special they have the per-ate anion which is more oxygen-rich and important here.) Assume the maximum possible oxidation state for the non-oxygen atom. Assume $-\mathrm{II}$ oxidation state for every oxygen. Add up and take the negative value to arrive at the charge.
A hydrogen- will add $\ce{H}$ and lower the charge by one.
A thio- means one oxygen is replaced by sulphur.
A di- means take two of the (hydrogenated) anion and subtract water. Pyro means the same thing.
Memorise all the remaining! That is most importantly:
Periodic Table
More
VOTE