Polyatomic Ions
The ions they need to know are on p 100 of the text. They need to know:
Name, formula, charge.
There are 22 that they need to know but there are a couple of tricks that will reduce them to 13.
Trick 1:
If they remember the ion that ends with “ate” they will know 3 others.
Example: chlorate - ClO3- (this is 1- but in chemistry we don’t write the 1’s)
If there is another oxygen, it is ClO4- and is perchlorate (as in short for hyper= above)
ClO3- - what we started with
If there is 1 oxygen less, it is ClO2- and is called chlorite
If there is 2 oxygens less, it is ClO- and is called hypochlorite (hypo means below)
All of the series has the same charge, -.
Example: phosphate, PO43- this is the “ate”
One more oxygen: PO53-, perphosphate
PO43- the “ate”
One less oxygen PO33- is phosphite
Two less oxygens PO23- hypophosphite
They all have a charge of 3-
Trick 2:
If a hydrogen is added to the ion because hydrogen is 1+ then the charge on the ion is 1 less
negative.
Example: carbonate, CO32Add 1 hydrogen making it:
hydrogen carbonate, HCO3-c
Example: phosphate, PO43Add 1 hydrogen making it:
hydrogen phosphate, HPO42Add another hydrogen
dihydrogen phosphate H2PO4Classes have come up with their own paragraphs to help them remember the ions. They are given
below.
Per 1
Dye found 7 crows and a 4th soulmate while using 4 chromebooks.
(Cr2O7-dichromate, SO4-sulfate, CrO4-chromate)
They took 3 cars out to 2 negative dates. (CO3-carbonate, O2 – peroxide, 2-)
Three Chloes were playing with 3 men and went out 3 nights. They came home to the house at 3:02.
(ClO3 - chlorate, MnO3 – manganate, NO3 – nitrate, C2H3O2- acetate)
A faucet leaked for 3 days. They weren’t see-ng 1 problem. Nate got hurt for fixing 1 faucet. Oh no he
drowned in 1 minute. (PO43-, CN-, NH4+, OH-)
Per 2
Look at the man go, go, go. Cho ran a mile in 2:32. I think no, no, no after he tripped over a 3 leaf clover.
1 man down.
(MnO3 – manganate, C-H-O, 2:32 = C2H3O2 - acetate, NO3 – nitrate, ClO3 – chlorate, 1-)
Four crows came out at 3. 2 died at 7. I shouted 4 times to 2 friends with no response.
[(CrO4 – chromate; Cr2O7 – dichromate; SO4 – sulfate, O2 – peroxide, -2(2 friends did not respond)]
Per. 3
MANiC
Manny asked Granny for 3 pansies. (MnO3 – manganate)
See to Ace, he dropped to 3rd place, OHH 2 cars was a waste (C2H3O2 – acetate)
Nate baked 3 bad cakes because he begged for 1 egg. (NO3 – nitrate; one neg = 1 egg – 1-)
Clark sailed in the ark 3 days. (ClO3)
My perfect pair of shoes had 4 holes in the soles. (O2 – peroxide, SO4 – Sulfate)
A man in a tunic crashed 3 cars when the 4 chrome wheels died and killed 7 oxen.
(Tunic = 2 neg – 2--; CO3 – carbonate; CrO4 – chromate; Cr2O7 – dichromate)
Mufassa got run over by 4 oxen in 3 sec in Ohio at -1o. He was positively stinky in 4 hrs This was all done
in the cartoon network at 1 AM.
(PO43-phosphate; OH- 1--; NH4 1+ ammonium; CN- cyanide)
Per. 4
MANiC
Manny asked Granny for 3 pansies. (MnO3 – manganate)
See to Ace, he dropped to 3rd place, OHH 2 cars was a waste (C2H3O2 – acetate)
Nate baked 3 bad cakes because he begged for 1 egg. (NO3 – nitrate; one neg = 1 egg – 1-)
Clark sailed in the ark 3 days. (ClO3)
There was a 3 car crash. Four chrome wheels were lost, 7 people died, 4 soulmates survived. 2 cats died.
To be continued...
(CO3 - carbonate; CrO4 – chromate; Cr2O7 – dichromate; SO4 – sulfate, O2 – peroxide; 2-)
A faucet leaked for 3 days. They weren’t see-ng 1 problem. Nate got hurt for fixing 1 faucet. Oh no he
drowned in 1 minute. (PO43-, CN-, NH4+, OH-)
Writing a Balanced Formula
The compounds that students will be asked to balance have a positive part (called cations) and a
negative part (called anion).
To write a balanced formula they need to write the cation with the charge. If it is just one element then
they can get the charge from the periodic table. The students are expected to know that all of the
elements in column 1 have a charge of + (said “one plus” but in chemistry we don’t write the 1’s)
Column 2 is 2+; column 3 is 3+; column 4 is 4+ & 4-; column 5 is 3-, column 6 is 2-, column 7 is – (said
“one minus” but we don’t write the 1’s); column 8 is neutral.
If an ion has more than one possible ion, it will be given on the periodic table that they use on a test.
See periodic table on the next page.
Ex: calcium and phosphorus
Ca2+ & P3Cross the numbers of the charges and put them as subscripts. Ca3P2
This will make the positive charge balance with the negative charge.
2+
x 3 = 3- x 2
Ex: sodium and sulfur. Na+ & S2- since in chemistry we do not write the 1s it becomes
Na2S when the charge numbers are crossed.
If the charges can have a number factored out of it, that needs to be done.
Ex: palladium(IV) and sulfate = Pd4+ & SO42- A 2 can be factored out of 4 & 2 so the balanced
formula is Pd2+ & SO4- Pd(SO4)2
If one of the charged parts is a polyatomic (= “many atoms”) ion from page 100, it is treated as a whole
Ex: potassium & carbonate
K+ & CO32- becomes K2CO3
(If there is only 1 of the polyatomic ions, no parentheses are needed.)
Ex: aluminum and carbonate Al3+ & CO32- becomes Al2(CO3)3 Because there are 3 carbonate
ions, there needs to be parentheses around it.
To go from the formula to name, see the flowchart on the next page. Have your student explain how it
works.