objectives l psc.2.2.3 –predict chemical formulas and names for simple compounds based on...
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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.
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.
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.
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.
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.
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.
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
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
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.
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
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
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
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.
Problems Write the formulas for the following
ternary ionic compounds.Ammonium chloride
Ammonium sulfide
NH4Cl
(NH4)2S