Download 400 Formula and Naming Notes

400 Chemistry
Formulas and Naming of Ions and Compounds
Information Conveyed by a Formula:
1. Which elements are present (chemical symbols)
2. The relative amount of each element present (subscripts which go with the
element to their left)
3. Any net charge on the species (# followed by a + or – sign for ions, net charge
on a compound is = 0 )
Note: Numbers outside parentheses multiply by all subscripts inside
parentheses, numbers in front of formulas multiply by all subscripts in a
formula. If no number is given, the quantity is one.
Examples:
H2O = hydrogen and oxygen combined so that for every 2 hydrogens, there is 1
oxygen
Na2CO3 = 2 sodiums, 1 carbon, and 3 oxygens (or 2 sodium ions and 1 carbonate
ion)
H2SO4 =
KI =
(NH4)3PO4 = 3 nitrogens, 12 hydrogens, 1 phosphorous, 4 oxygens OR 3
ammonium ions (that’s the one in parentheses) and 1 phosphate ion
CuSO4 ∙ 5 H2O = 1 copper, 1 sulfur, 9 oxygens, 10 hydrogens OR 1 copper ion
and 1 sulfate ion and 5 waters
BaCl2 ∙ 2 H2O =
Recognizing Different Types of Formulas (we name things based on what type they
are):
-If it has a charge, it is an ion
-If it starts with H, it is an acid
-If it is made up of a metal and a nonmetal, it is an ionic compound
-If it is made up of 2 nonmetals, it is a molecular compound
-If it has a polyatomic ion in it, it is an ionic compound (more on that soon!)
Examples:
K+
HCl
OH-
CO
NaCl
BaSO4
NaOH
PCl5
Mg2+
F-
Ions
Ion Charges and Oxidation Number
Atom = smallest particle of an element that still retains the properties of that
element
Atoms have three subatomic particles: protons (positive charge), neutrons
(neutral, no charge), electrons (negative charge)
In a neutral atom, the number of protons is equal to the number of
electrons (so a neutral atom has NO charge)
Ion = a charged atom (number of protons and electrons is not equal)
Cation = a positively charged ion (has more protons than electrons, has lost
electrons)
Anion = a negatively charged ion (has more electrons than protons, has gained
electrons)
Representative elements (A groups on Periodic Table) can be assigned a charge or
oxidation number based on their location (group or family): 1+, 2+, 3+, 4+, 3-, 2-,
1-, 0 going across from left to right
Transition elements (for reasons we’ll discuss later) can have multiple charges
and there is not an obvious way to memorize them
Some common cation charges can be memorized by using the following “chant”
which groups elements with “unusual” charges with ones we know due to their
group location:
Pronounce it as it looks!
HAgLiNaKCu
HAgLiNaKCu
CuBaCaFePbZnMg
AlFeSbBiCr
AlFeSbBiCr
SiC, SiC, SiC
(1+)
(2+)
(3+)
(4+)
How to Name Ions
Cations: Just use the full element name, followed by “ion” or “cation”
Ex: K+ potassium ion, Ca2+ calcium cation
Anions: Use the element root and add “ide” to the end, followed by “ion” or
“anion”
Ex: Cl- chloride anion, O2- oxide anion, P3- phosphide ion
Some cations (especially transition metals) can have more than one charge
To be clear, we must indicate the charge that we mean
Ex: Cu1+ is copper(I) or cuprous, Cu2+ is copper(II) or cupric
So charge can be indicated in a name with a roman numeral in parentheses or by
using the Latin/Greek root for the element with an –ic or –ous ending (-ic for the higher
of the charges, -ous for the lower)
Other common ones are: iron(II) and iron(III), mercury(I) and mercury(II),
lead(II) and lead(IV), tin(II) and tin(IV), and various charges for chromium and
manganese
So far, we have been dealing with monatomic ions
Monatomic ion = ion consisting of only one element (and atom)
Polyatomic ion = group of atoms held together with a net charge (very important
in many of the compounds we will use!)
Polyatomic Ions
Essential for naming and writing formulas for compounds!
Some must be memorized, some can be derived from the ones you memorize!
Here’s the list- memorize these (the names and formulas with charges)… and then we
will have rules to help you derive any others you need!
Cations
NH4+ ammonium
Hg22+ mercury(I)
Anions
ClO3- chlorate
NO3- nitrate
CO32- carbonate
SO42- sulfate
PO43- phosphate
CN- cyanide
CNO- cyanate
OH- hydroxide
C2H3O2- acetate
C2O42oxalate
MnO4
permanganate
CrO42chromate
Cr2O72dichromate
How to Derive Other Names
1. If the formula is similar to one on the list but has 1 less oxygen, change the ending
to “ite”
2. If the formula is similar to an “ite” polyatomic ion but has 1 less oxygen than that
one, add the prefix “hypo” and keep the “ite” ending
3. If the formula is similar to one on the list but has 1 more oxygen, keep the usual
ending but add the prefix “per”
4. If 1 hydrogen appears in the formula, add “hydrogen” or “monohydrogen” to the
name; if 2 hydrogens appear in the formula, add “dihydrogen” to the name
5. If an oxygen in a formula is replaced with a sulfur, add “thio” as a prefix
6. Don’t forget to use the Periodic Table… elements in the same group behave
similarly and are named similarly
Examples….
BrOSiO32AsO43CNSO22HCO3HAsO42H2AsO4SO32S2O32Answers: hypobromite, silicate, arsenate, thiocyanate, peroxide, hydrogen carbonate,
hydrogen arsenate, dihydrogen arsenate, sulfite, thiosulfate
Naming From Formulas

Molecular (covalent) – use prefixes to indicate the number you have of
each element (but never use mono for the first one listed), -ide ending
o 1 = mono
o 2 = di
o 3 = tri
o 4 = tetra
o 5 = penta
o 6 = hexa
o 7 = hepta
o 8 = octa
o 9 = nona
o 10 = deca


Ionic – name the cation first, followed by the anion, -ide ending if
monatomic ions… -ide, -ite, or –ate for polyatomic ions
o If it contains a cation that can have more than one charge, use a
roman numeral to show the charge
Hydrates - First, name the compound. Then add a prefix to indicate the
number of waters. Then add the word “hydrate” to the end.
Ex: CuSO4 ∙ 5 H2O is copper(II) sulfate pentahydrate

Elements that are diatomic molecules in nature:
Seven elements (hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine,
iodine) appear in nature as diatomic molecules. For these elements, even though
we see the formula written with 2, we simply identify them by using the element
name.
Ex: O2 is oxygen, H2 is hydrogen
To remember these elements, use one of the following mnemonic devices:
“Horses Need Oats For Clear Brown “I”s” Or “I Never Fish On His Clean Brook”
Or the Billy J rule (I don’t like this one but silly students seem to!) “BrIFClOHN”

Acids:
o Binary (H plus one element): hydro- root of element –ic acid
o Converting Polyatomic Ion Names Into Acid Names:
Use the following mnemonic device to help…
“I ATE something ICky, I mITE get nauseOUS” So, polyatomic ions with
names ending in “ate” will produce acids with names ending in “ic”, and
polyatomic ions with names ending in “ite” will produce acids with names ending
in “ous”
Writing Formulas from Names
To write a formula for an ionic compound or acid:
1. Using the name, write down the formulas and the charges for the ions involved (if
an acid make sure to determine which ions are present first by invoking the
naming rules)
2. Use the criss-cross rule to determine the subscripts (see demo on board)
3. Reduce the subscripts if necessary (they should be the lowest whole numbers
possible)
4. To use subscripts with polyatomic ions, put parentheses around the polyatomic
ion with the subscript on the outside
5. Once you have a formula and you believe it is correct, check to make sure that the
net charge on the compound is equal to ZERO
To write a formula for a molecular compound:
1. Use the prefixes in the name of the compound to determine how many of each
element are present
2. Write a formula where you express those prefixes as subscripts