Molecules And Compounds - Chemistry Worksheet Page 4
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9POLYATOMIC IONS
– Know the formulas and names of the following polyatomic ions:
+
2–
2–
NH
= ammonium ion
CrO
= chromate ion
CO
= carbonate ion
4
4
3
2+
2–
–
Hg
= mercury (I) ion
Cr
O
= dichromate ion
HCO
= bicarbonate or
2
2
7
3
2–
SO
= sulfate ion
hydrogen carbonate ion
4
–
2–
–
MnO
= permanganate ion
SO
= sulfite ion
ClO
= hypochlorite ion
4
3
–
–
–
C
H
O
= acetate ion
NO
= nitrate ion
ClO
= chlorite ion
2
3
2
3
2
3–
–
–
PO
= phosphate ion
NO
= nitrite ion
ClO
= chlorate ion
4
2
3
–
–
–
CN
= cyanide ion
OH
= hydroxide ion
ClO
= perchlorate ion
4
–
2–
SCN
= thiocyanate ion
O
= peroxide ion
2
FORMULAS OF IONIC COMPOUNDS
– indicate the number of cations and anions present using symbols and subscripts
→
Compounds must be neutral
positive (+ve) charges = negative (-ve) charges
How to write chemical formulas of ionic compounds:
1. If both ions have charges that are exactly opposite (+1 & -1, +2 & -2, etc.),
→
the compound’s formula contains one of each ion
– This also applies for polyatomic ions.
→
→
+
–
+
–
Na
+ Cl
NaCl
and
Na
+ CN
NaCN
→
→
+
–
+
–
K
+ Cl
___________
K
+ NO
______________
3
→
→
2+
2–
2+
2–
Mg
+ O
___________
Mg
+ SO
______________
4
→
→
3+
3–
3+
3–
Al
+ N
___________
Al
+ PO
______________
4
2. For monatomic ions with different charges, use the crossover method:
→
Make the number on the negative charge the subscript of the cation and the number on
the positive charge the subscript of the anion.
– Do NOT bring down the signs (+ or –), just the numbers!
2+
–
3+
2–
+
3–
Ba
+
Cl
Al
+ O
K
+
P
CHEM 139: Tro Chapter 5
page 4 of 9
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