Download 1. NAMING A COMPOUND GIVEN ITS FORMULA Ionic

1. NAMING A COMPOUND GIVEN ITS FORMULA
Ionic Compounds:
Covalent/Molecular Compounds:
contain a METAL and NONMETAL
contain NONMETALS (and/or metalloids)
The following elements are nonmetals or
metalloids:
H, B, C, N, O, F, Si, P, S, Cl, Ge, As, Se, Br, Sb,
Te, I, At (you don’t have to memorize these, just look at
or a polyatomic ion (listed on Table E)
(metals are on the left side of the staircase,
nonmetals are on the right)
Steps:
Steps:
1.
Write the name of the first element (metal)
2.
Write the name of the second element (nonmetal)
with an “ide” ending
OR the full name for a polyatomic ion Ref.
Table E
3.
4.
where they are located on the periodic table)
Only put a roman numeral after the name of the
metal if there is more than one oxidation state to
choose from for that metal. The Roman numeral
goes right after the name of the metal because it
stands for the charge of the METAL ION. Put the
Roman numeral in parentheses.
To determine the charge of the metal ion, first look
up the charge on the NONmetal ion and write it
above the NONmetal symbol. The NONmetal will
ALWAYS have a NEGATIVE charge, the metal will
ALWAYS have a positive charge. Balance the
negative charges on the nonmetal by choosing a
positive charge for the metal ion that will cancel out
the total negative charges on the NONmetal.
1. Write the full name of the first element. If it
has a subscript, turn it into the Greek prefix
on the element’s name
2. Write the name of the second element with an
“ide” ending. If it has a subscript, turn the
subscript into the Greek prefix on the
element's name
*NEVER put “mono” in front of the 1st element
*Drop the last vowel of the prefix if the element
begins with the SAME vowel
mono = 1
di = 2
tri = 3
tetra = 4
nono = 9
Examples:
Greek prefixes
penta = 5
hexa = 6
hepta = 7
octo = 8
deca = 10
Formula
NaCl
Name
sodium chloride
Examples:
Formula
Name
CuCO3
copper(II) carbonate
CO
carbon monoxide
SO2
sulfur dioxide
PCl3
phosphorus trichloride
As2S3
diarsenic trisulfide
(because the carbonate ion has a 2- charge and there is one
carbonate ion and one copper ion in the formula, the
charge on the copper ion must be 2+ because the
compound overall is neutral.)
Cu2CO3
copper(I) carbonate
(because the carbonate ion has a 2- charge and there is one
carbonate ion and two copper ions in the formula, the
charge on each copper ion must be 1+ because the
compound overall is neutral: two 1+ charges cancel one
2- charge)
Al2O3
aluminum oxide
Sr(NO3)2
strontium nitrate
2. DETERMINING THE FORMULA OF A COMPOUND FROM ITS NAME
For IONIC Compounds (metal + nonmetal elements)
Steps
1. Write the symbols for the elements
2. Write the oxidation numbers in the upper right corner of each symbol
* Remember to put polyatomic ions in parentheses ( )! Treat them as if they were one element.
* If there is a Roman numeral in parenthesis after the name of the metal, that is the charge on the metal
ion, so write that above the metal symbol. Example: in the compound iron(III) oxide, the iron ion has
a charge of 3+, which we would write as Fe3+
3. If the positive charge on the metal ion equals the negative charge on the nonmetal ion, that is the
formula for the compound
4. If the positive charge on the metal ion does not equal the negative charge on the nonmetal ion, Crisscross the numbers and put as subscripts for the opposite symbol – put only the NUMBER as the
subscript, do not bring the sign with it. ***Remember, IONIC formulas are ALWAYS written as
empirical (simplest ratio), so if you can simplify the formula by dividing both subscripts by the same
number, do so.
5. Check: multiply each ion’s charge by its subscript  overall charge should be zero
Examples: final answers in bold
a.
b.
c.
d.
e.
f.
g.
What is the formula for sodium nitride?
What is the formula for barium hydroxide?
What is the formula for potassium thiosulfate?
What is the formula for ammonium chloride?
What is the formula for chromium (II) oxide?
What is the formula for chromium (III) oxide?
What is the formula for chromium (VI) oxide?
Na1+ N3Ba2+(OH)1K1+ (S2O3)2(NH4)1+ Cl1Cr2+O2Cr3+ O2Cr6+O2-
(criss-cross)  Na3N
(criss-cross)  Ba(OH)2
(criss-cross)  K2S2O3
 NH4Cl
 CrO
(criss-cross)  Cr2O3
(criss-cross)  Cr2O6
***simplifies to CrO3
For Covalent/Molecular Compounds (nonmetal elements and/or metalloids)
Steps
1. Write the symbol for the first element given. If it has a Greek prefix, it becomes the subscript on the
symbol. If it does not have a Greek prefix, there is only one of that atom in the formula, so it does not
have a subscript.
2. Write the symbol for the second element given. The Greek prefix becomes the subscript on the symbol.
Examples: final answers in bold
a. What is the molecular formula for carbon tetrachloride?
b. What is the molecular formula for sulfur pentafluoride?
c. What is the molecular formula for arsenic tribromide?
d. What is the molecular formula for dihydrogen monoxide?
e. What is the molecular formula for diphosphorus pentoxide?
f. What is the molecular formula for antimony trichloride?
g. What is the molecular formula for tellurium difluoride?
CCl4
SF5
AsBr3
H2O
P2O5
SbCl3
TeF2