S. 4.2 – Naming Inorganic Compounds
Chemical Formulas
-
Combination of symbols representing a compound.
Ex. Waters chemical formula is H2O.
What the formula tells us.
- Which elements are in the compound.
H = hydrogen, and O = oxygen.
- Subscripts tell us how many of that element are in the compound.
Subscript 2 after H = 2 hydrogen atoms are in the compound.
No subscript after O = 1 oxygen atom.
- Addition of subscripts tell us how many atoms make up the compound.
- 2 + 1 = 3 atoms.
Table 1: Examples of chemical compounds.
Compound Name
Sodium chloride (table salt)
Calcium carbonate (chalk)
Copper sulphate
Sodium hydrogen carbonate.
(Backing soda)
Chemical Formula
NaCl
CaCO3
CuSO4
NaHCO3
Ratio of atoms
1 Na : 1 Cl
1 Ca : 1 C : 3 O
1 Cu : 1 S : 4 O
1 Na : 1 H : 1 C : 3 O
Molecules
- When non-metal atoms join together they form a molecule.
- Ex. H2O – water and H2O2 – hydrogen peroxide.
Molecules of elements
- When two or more of the same non-metal are put together.
- Ex. O2, H2, S8.
- 7 elements exist in nature as diatomic atoms (diatomic meaning that there are two atoms in a compound).
1) Hydrogen gas – H2.
2) Nitrogen gas – N2.
3) Oxygen gas – O2.
4) Fluorine gas – F2.
5) Chlorine gas – Cl2.
6) Bromine – Br2.
7) Iodine – I2.
Naming Monovalent metal Compounds
Monovalent metal:
Multivalent metal:
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What’s in a name?
Combining capacity
-
Combining of elements into compounds using combining capacity.
Putting calcium and nitrogen together (calcium nitride).
Putting sodium and chlorine together (sodium chloride).
Putting calcium and oxygen together (calcium oxide).
Note, when combining capacities are equal, we do not write down the charge value as a subscript value in the
compound formula.
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Naming steps,
1) Name the metal.
2) Name the non-metal and change the ending to “ide”.
Ex. LiCl
1)
2)
Ex. MgO
1)
2)
Naming Multivalent Metals.
Multivalent element
- Element that can form more than one stable ion.
- Most metals in the middle of the table.
Ex. Fe2+ = iron (II) and Fe3+ = iron (III).
Ex.
Name
Nickel (III) sulphide
Manganese (IV) sulphide
Manganese (III) sulphide
Manganese (II) sulphide
Formula
Ni2S3
MnS2
Mn3S2
MnS
Rules for writing names of multivalent ionic compounds.
1. Name the metal ion.
2. Look at the periodic table to see if the metal has more than one combining capacity.
3. Determine the combining capacity’s of the metal by looking at the formula of the compound. (Look at
the non – metals subscript, usually you can un – criss cross the value, but remember that the subscripts
may be in lowest ratio value.
4. In brackets write the metals combining capacity in roman numerals.
5. Name the non – metal with the ending “ide”.
Ex. Cr2O3
1.
2.
3.
4.
5.
3
Ex. CoP
1.
2.
3.
4.
5.
Rules for writing formula of multivalent ionic compounds.
1. Identify each ion and its charge. Ex. chromium (III) nitride = Cr3+ N3-
Cr3+ N3-
2. Criss cross charges. Ex.
3. Put the symbols together and get rid of the charge values. Ex. Ca3N2
4. If subscript ratio is not the smallest possible ratio, make them into the smallest possible ratio. Ex. Cr3N3
= CrN.
Ex. copper (I) selenide
1) Cu1+ Se2-
+
Cu
Criss cross charges
2)
3) Cu2Se
Se2-
Naming Polyatomic ions.
Polyatomic ions.
- Group of atoms covalently bonded with a charge.
- Ions comprised of more than one atom.
- Atoms share electrons.
Common polyatomic ions.
Ion Name
Ion Formula
Positive Ions
ammonium
NH4+1
Mercury (I)
Hg2+2
Negative ions
Hydrogen carbonate HCO3-1
Or bicarbonate
hydroxide
OHethanoate
CH3COO-1
Or acetate
carbonate
CO3-2
chromate
CrO4-2
dichromate
Cr2O7-2
Sulphate
SO4-2
Sulphite
SO3-2
phosphate
PO4-3
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Writing names of compounds with polyatomic ions.
Rules for writing names from formulas for compounds with polyatomic ions.
1. Write the positive ions name, either will be a metal or ammonium (NH4+).
2. Determine if the metal is a multivalent ion. If it is, remember to indicate the multivalent ions charge in
roman numerals.
3. Identify the negative ion and name it.
Ex. Cr3(PO4)2
1.
2.
3.
Notice that we can un – criss cross the subscript numbers to get the combining capacity.
Basically, familiarize yourself with the above polyatomic ions. Only with practice will you be able to identify
the polyatomic ions quickly.
Rules for writing the formula of a compound from name.
1. Identify each ion and its charge. Ex. chromium (III) sulphate = Cr3+ SO4-2
Cr3+
SO4-2
2. Criss cross charges. Ex.
3. Put the symbols together and get rid of the charge values. For polyatomic ions, use brackets around the
ion. The whole ion has the subscript value. Ex. Cr2(SO4)3
Naming Hydrates.
Hydrates:
Crystallized ionic solids:
Ex. When aluminum oxide crystallizes from water, the resulting crystals have a formula of :
Prefix:
- A word representing a number indicating how many of something there are.
- There are 10 prefixes that you need to know.
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Learn these prefixes b/c these are the prefixes used for naming polyatomic compounds.
Prefix
# of water molecules
or # of atoms
mono
1
di
2
tri
3
tetra
4
penta
5
Hexa
6
hepta
7
octa
8
nona
9
deca
10
Steps to naming Hydrates:
1. Name the compound as you would normally do so.
2. After the compound name, place the corresponding prefix (# of water molecules) in front of the
word hydrate.
Ex’s.
1) FeSO4·5H2O =
2) NiSO4·7H2O =
3) Co3(PO4)2·8H2O =
Questions:
- Pg. 71, # 4.
- Pg. 72, # 5.
- Pg. 73, # 6,7
Names and Formulas of Binary Molecular Compounds.
Intro:
-
Covalent compounds.
Subscripts of molecular compounds indicate the number of atoms in the compound.
Never reduced the subscripts for covalent compounds, only for ionic compoundsd.
Binary = two types of atoms in a compound.
Ex. N2O4 remains as N2O4, not NO2 (these two compounds are not the same).
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Rules for Naming Binary Molecular Compounds.
Naming.
Steps
1) Identify the subscript value of the first element.
2) Write down the prefix correlating to step one.
3) Write down the first atoms name (no space between prefix and element name).
4) Space.
5) Identify the subscript value of the second element.
6) Write down the prefix correlating to step five.
7) Write down the seconds atoms name, ending in “ide” (no space between prefix and element name).
Exceptions:
1) If first element has one atom, do not add the prefix mono.
2) Prefix mono is shortened to mon if placed infront of an element that starts with “o”.
3) Do not reduce prefixes ie. N2O4 = dintrogen tetraoxide ≠ NO2 = nitrogen dioxide
Ex. N2O4
1)
2)
3)
4)
5)
6)
7)
Ex. NO
1)
2)
3)
4)
5)
6)
7)
Some Common Acids:
Acid: Chemical starting with H and when dissolved in water donate hydrogen to water to make
hydroneum H3O+.
Ex. HF = hydrofluoric acid, H2SO4 = sulphuric acid, HCl = hydrochloric acid.
READ: Pg. 74 and outline some common uses for acids.
Questions:
- Pg. 74, # 8, 9.
- Pg. 75 and 76 all . Try and do as many as you can to understand the material.
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