1. Chemical Formulas and chemical compounds

2. Objectives: Explain the significance of a chemical formula.
Determine the formula of an ionic compound formed between two given ions.
Name an ionic compound given its formula.
Using prefixes, name a binary molecular compound from its formula.
Write the formula of a binary molecular compound given its name.

3. Chemical names and Formulas
There are millions of natural and synthetic chemical compounds
Calcium carbonate – limestone
Sodium chloride – table salt
Dihydrogen monoxide – water
These are their chemical and common names
Chemical names help to describe the atomic makeup of the compounds

4. Significance of a Chemical Formula
Indicates the relative number of atoms of each kind in a chemical compound.
Molecular formula
Indicates the relative number of atoms of each kind in a molecule. (Covalently bonded)
C8H18
Subscript indicates there are 8 atoms of carbon in a molecule of octane
Subscript indicates there are 18 atoms of hydrogen in a molecule of octane

5. Al2(SO4)3 Chemical formula for ionic compound
Ionic compound consists of lattice of positive and negative ions held together by mutual attraction.
Chemical formula represented by one formula unit
Simplest ratio of the compounds positive and negative ions
Aluminum sulfate below consists of aluminum cations and sulfate ions
Al2(SO4)3
Subscript 3 refers to everything inside the parentheses giving 3 sulfate ions, with a total of 3 sulfur atoms and 12 oxygen atoms
Subscript 2 refers to 2 Aluminum atoms
Subscript 4 refers to 4 oxygen atoms in the sulfate ion
Note: when you only have one of an atom, no subscript is used
Note: parentheses are used to identify polyatomic ion as one unit

6. Monatomic ions Ions formed from a single atom
Examples
Na+1 lose one electron
Mg2+
S2- gain two electrons
N-3
Cl1-
Not all main-group elements readily form ions
Examples
Carbon & Silicon form covalent bonds
d-block elements form variable charges
examples
Copper, can be Cu+1 or Cu+2
Iron, can be Fe+2 or Fe+3
Lead, can bePb+2, Pb+3, or Pb+4

7. Naming Monatomic ions Positive ions Negative ions Name of element
Ex: K Potassium
Mg Magnesium
Al __________
Sr __________
Negative ions
Base of element + -ide ending
Ex: F Fluoride
N Nitride
O _______
Br _______

8. Binary Ionic Compounds
Compounds composed of two different elements
Total # of positive charges must be equal to total # of negative charges
Writing formulas, Ex: Aluminum oxide
Write the symbols for ions (Cation first)
Al+3 O-2
Cross over the charges as subscripts
Al2O3
Check to make sure total charges are equal, divide by largest number, to give smallest whole-number ratio +3 -2
2 x (+3) = +6
3 x (-2) = -6

9. Naming binary ionic compounds
Nomenclature
Naming system
Name Al2O3
Name cation first : full name of cation
Aluminum
Name Anion last : base of anion + -ide
oxide
Al2O3
aluminum oxide

10. Practice Naming and Writing Formulas
Name
AgCl
ZnO
SrF2
silver chloride
zinc oxide
strontium fluoride
Write the formulas for
Zinc iodide
Zinc sulfide
Aluminum sulfide
ZnI2
ZnS
Al2S3

11. Stock System of Nomenclature
Some cations may have two or more different charges
Use stock system of naming (usually with d-block elements)
Roman numeral represents charge in parentheses
Fe+2 Fe+3
Iron(II) Iron(III)
Some cations that commonly form only one cation
Do not use roman numerals ( main group elements)
No Anions form more than one charge +2 -1
CuCl2
copper(II)
chloride

12. Practice stock system
Write formula and give name for compound formed by ions Cr+3 and F-1
CrF3
chromium(III) fluoride
Write formulas and give name for the following ionic compounds:
Cu+2 and Br-1
CuBr2
copper(II) bromide
Fe+2 and O-2
FeO
iron(II) oxide
Fe+3 and O-2
Fe2O3
iron(III) oxide

13. Compounds containing Polyatomic Ions
All but NH4+, ammonium ion, are negatively charged
Most are oxyanions
Examples
NO NO2-1
nitrate
nitrite
Most common anion has –ate ending
Anion with one less oxygen has –ite ending
Anion with two less oxygen has hypo prefix and –ite ending
Anion with one extra oxygen has per prefix and –ate ending
ClO3-1
ClO2-1
ClO-1
ClO4-1
hypochlorite
perchlorate
chlorate
chlorite

14. Naming Compounds with Polyatomic Ions
Same as naming for ionic compounds except
Name polyatomic ion as one unit
Example:
AgNO3
Use parentheses if more than one polyatomic ion
Example
Al2(SO4)3
silver nitrate
Show 2 Al+3 ions and 3 SO4-2 ions
aluminum sulfate

15. Writing Formulas and Naming Compounds with Polyatomic Ions
Write the formula for these:
tin(IV) sulfate
calcium chloride
lithium nitrate
calcium nitrite
potassium perchlorate
Sn(SO4)2
CaCl2
LiNO3
Ca(NO2)2
KClO4
Write the names for these:
Ag2O
Ca(OH)2
NH4OH
FeCrO4
KClO
silver oxide
calcium hydroxide
ammonium hydroxide
iron(II) chromate
potassium hypochlorite

16. Naming Binary Molecular Compounds
May use stock system to name these
New system – must understand oxidation numbers
Prefix system
Old system – must know numerical prefixes
mono-
di-
tri-
tetra-
penta-
hexa-
hepta-
octa-
nona-
deca-

17. Rules for prefix system of Nomenclature
less-electronegative element is given first
Second element is named by combining
Prefix indicating number of atoms
Root of name of second element
-ide ending
First element only gets a prefix if it has more than one
Ex: P4O10
Ex:
tetra
phosphorus
dec ox
ide
The o or a at the end of a prefix is usually dropped when the word following the prefix begins with another vowel

18. The 6 binary compounds of Nitrogen and Oxygen
N2O NO
NO2
N2O3
N2O4
N2O5
dinitrogen
monoxide
nitrogen
monoxide
nitrogen
dioxide
dinitrogen
trioxide
dinitrogen
tetroxide
dinitrogen
pentoxide
Name the following molecular compounds
Write formulas for the following molecular compounds
SO3
ICl3
PBr5
sulfur trioxide
carbon tetraiodide
phosphorus trichloride
oxygen difluoride
CI4
iodine trichloride
PCl3
Phosphorus pentabromide
OF2