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Objectives. PSc.2.2.3 Predict chemical formulas and names for simple compounds based on knowledge of bond formation and naming conventions. Naming Compounds and Writing Formulas. Systematic Naming. There are too many compounds to remember the names of them all. - PowerPoint PPT Presentation
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ObjectivesObjectives PSc.2.2.3
–Predict chemical formulas and names for simple compounds based on knowledge of bond formation and naming conventions.
Naming Compounds and
Writing Formulas
Systematic Naming There are too many compounds to
remember the names of them all. A compound is made of two or more
elements. The name should tell us how many and
what type of atoms.
Types of Compounds There are two types of compounds: ionic
compounds and molecular (covalent) compounds.
Ionic Compounds The simplest ratio of the ions
represented in an ionic compound is called a formula unit.
The overall charge of any formula unit is zero.
In order to write a correct formula unit, one must know the charge of each ion.
2+1+
3+ 3- 2- 1-
Charges on Ions:Oxidation Numbers
Naming Cations
We will use the systematic way. For cations, if the charge is always the
same (Group A) just write the name of the metal.
Naming Cations
Tin and lead can have more than one type of charge.
Indicate the charge with Roman numerals in parenthesis.
Example Li1+
Li is the symbol for lithium.
Lithium is a Group 1A metal, so the charge is always the same. Write the name of the metal.
Li1+ is called the Lithium ion.
Example Sr2+
Sr is the symbol for strontium.
Strontium is a Group 2A metal, so the charge is always the same. Write the name of the metal.
Sr2+ is called the Strontium ion.
Example Sn2+
Sn is the symbol for tin.
Tin has multiple oxidation numbers. Write the name of the metal, indicating the charge with Roman numerals in parenthesis.
Sn2+ is called the Tin (II) ion.
Example Pb4+
Pb is the symbol for lead. Lead is a Group 4A metal, and the
charge is not always the same. Write the name of the metal, indicating the charge with Roman numerals in parenthesis.
Pb4+ is called the Lead (IV) ion.
Problem
Name the following cations.
Ca2+
Sn4+
Calcium ion Al3+ Aluminum ion
Tin (IV) ion
Naming Anions Naming monatomic anions is always the
same. Change the element ending to – ide Example: F1- F is the symbol for fluorine, F1- is
ide.fluor ine.
Example Cl1-
Cl is the symbol for chlorine.
Chlorine is a Group 7A nonmetal, so the charge is always the same (1-).
Cl1- is called the chloride ion.
Example O2-
O is the symbol for oxygen.
Oxygen is a Group 6A nonmetal, so the charge is always the same (2-).
O2- is called the oxide ion.
Problem Name the following anions.
S2- sulfide ion
Br1-bromide ion
N3-nitride ion
Problem Name the following anions.
As3- arsenide ion
Te2-telluride ion
Binary Ionic Compounds Binary ionic compounds are
composed of a metal bonded with a nonmetal.
Name the metal ion using a Roman numeral in parenthesis if necessary.
Follow this name with the name of the nonmetal ion.
Example Name the following binary ionic
compounds.
NaCl Sodium chloride
Ca3P2Calcium phosphide
Example Name the following binary ionic
compounds.
PbO Lead (II) oxide
SnBr2 Tin (II) bromide
Problem Name the following binary ionic
compounds.
Lead (IV) oxide
AlF3 Aluminum fluoride
PbO2
Problem Name the following binary ionic
compounds.
KCl Potassium chloride
Na3N Sodium nitride
Writing the Formulas for Cations
Write the formula for the metal. If a Roman numeral is in parenthesis
use that number for the charge. Indicate the charge with a superscript.
Writing the Formulas for Cations
If no Roman numeral is given, find the Group A metal on the periodic table and determine the charge from the column number.
Example Lead (II) ion
Pb is the symbol for lead.
Lead has multiple charges, which is the reason why the charge with Roman numerals in parenthesis was included.
The formula for the lead (II) ion is Pb2+.
Example Gallium ion
Ga is the symbol for gallium.
Gallium is a Group 3A metal and its charge is always the same (3+).
The formula for the gallium ion is Ga3+.
Problem
Write the formulas for the following cations.
Copper (II) ion
Magnesium ion
Potassium ion
Mg2+
Cu2+
K1+
Problem
Write the formulas for the following ions.
Chromium (VI) ion
Aluminum ion
Mercury (II) ion
Al3+
Cr6+
Hg2+
Writing the Formulas for Anions
Write the formula for the nonmetal. Find the Group A nonmetal on the
periodic table and determine the charge from the column number.
Problem Write the formulas for the following anions.
iodide ion I1-
phosphide ion P3-
Problem Write the formulas for the following anions.
selenide ion Se2-
carbide ion C4-
Ionic Compounds Oxidation numbers can be used to
determine the chemical formulas for ionic compounds.
If the oxidation number of each ion is multiplied by the number of that ion present in a formula unit, and then the results are added, the sum must be zero.
Ionic Compounds In the formula for an ionic compound,
the symbol of the cation is written before that of the anion.
Subscripts, or small numbers written to the lower right of the chemical symbols, show the numbers of ions of each type present in a formula unit.
Writing Formulas for Binary Ionic Compounds
Write the symbol for the metal. Determine the oxidation number from either the column number or the Roman numeral and write it as a superscript to the right of the metal’s symbol.
Writing Formulas for Binary Ionic Compounds
To the right of the metal’s symbol, write the symbol for the nonmetal. Determine the oxidation number from the column number and write it as a superscript to the right of the nonmetal’s symbol.
Writing Formulas for Binary Ionic Compounds
Example: potassium fluoride
K 1+ F 1-
Writing Formulas for Binary Ionic Compounds
If the two oxidation numbers add together to get zero, the formula is a one-to-one ratio of the elements.
Writing Formulas for Binary Ionic Compounds
Example: potassium fluoride
K 1+ F 1-KF
Writing Formulas for Binary Ionic Compounds
Example: aluminum sulfide
Al 3+ S 2-
Writing Formulas for Binary Ionic Compounds
If the two oxidation numbers DO NOT add together to get zero, you will need to “criss-cross” the superscripts. These numbers now become subscripts.
Writing Formulas for Binary Ionic Compounds
Example: aluminum sulfide
Al 3+ S 2-
3+2-
Writing Formulas for Binary Ionic Compounds
Omit all positive and negative signs and omit all 1’s.
Writing Formulas for Binary Ionic Compounds
Example: aluminum sulfide
Al S2 3Al2S3
Problem
Lithium selenide
Write the formulas for the following binary ionic compounds.
Tin (II) oxide
Li2Se
SnO
Problem
Tin (IV) oxide
Write the formulas for the following binary ionic compounds.
Magnesium fluoride
SnO2
MgF2
Ternary Ionic Compounds Ternary ionic compounds are
composed of at least 3 elements. Name the metal ion, using a Roman
numeral in parenthesis if necessary. Follow this name with the name of the
polyatomic ion.
Polyatomic ions Polyatomic ions are groups of atoms that stay together
and have a charge. Examples include:
Nitrate NO3-1
Acetate C2H3O2-1
Hydroxide OH-1
Ammonium NH4+1
Carbonate CO3-2
Sulfate SO4-2
Phosphate PO4-3
Ternary Ionic Compounds There is one polyatomic ion with a
positive oxidation number (NH4+) that
may come first in a compound. Name the ion.
Follow this name with the name of the anion or second polyatomic ion.
Examples Name the following ternary ionic
compounds.Li2CO3
Al(OH)3
Lithium carbonate
Aluminum hydroxide
Examples Name the following ternary ionic
compounds.(NH4)2CO3 Ammonium carbonate
GaPO4 Gallium phosphate
Problems Name the following ternary ionic
compounds.
NaNO3 Sodium nitrate
CaSO4 Calcium sulfate
Writing Formulas for Ternary Ionic Compounds
Write the symbol for the metal or ammonium ion. Write the oxidation number as a superscript to the right of the metal’s/ammonium ion’s symbol.
Writing Formulas for Ternary Ionic Compounds
To the right of the metal’s symbol, write the symbol for the nonmetal or polyatomic ion. Write the oxidation number as a superscript to the right of the nonmetal’s/polyatomic ion’s symbol.
Writing Formulas for Ternary Ionic Compounds
Example: potassium nitrate
K 1+ NO31-
Writing Formulas for Ternary Ionic Compounds
If the two oxidation numbers add together to get zero, the formula is a one-to-one ratio of the elements.
Writing Formulas for Ternary Ionic Compounds
Example: potassium nitrate
K 1+ NO31-KNO3
Writing Formulas for Ternary Ionic Compounds
Example: aluminum sulfate
Al 3+ SO42-
Writing Formulas for Ternary Ionic Compounds
If the two oxidation numbers DO NOT add together to get zero, you will need to “criss-cross” the superscripts. These numbers now become subscripts.
Parentheses are to be placed around polyatomic ions before criss-crossing.
Writing Formulas for Ternary Ionic Compounds
Example: aluminum sulfate
Al 3+ SO42-
3+2-( )
Writing Formulas for Ternary Ionic Compounds
Omit all positive and negative signs and omit all 1’s.
Writing Formulas for Ternary Ionic Compounds
Example: aluminum sulfate
Al2(SO4)3
Problems Write the formulas for the following
ternary ionic compounds.Ammonium chloride
Ammonium sulfide
NH4Cl
(NH4)2S
Problems Write the formulas for the following
ternary ionic compounds.Barium nitrate
Lead (II) carbonate
Ba(NO3)2
PbCO3