Objectives l PSc.2.2.3 –Predict chemical formulas and names for simple compounds based on...

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


PbO Lead (II) oxide

SnBr2 Tin (II) bromide

Problem


Lead (IV) oxide

AlF3 Aluminum fluoride

PbO2

Problem


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.


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.


Example: potassium fluoride

K1+

F1-


If the two oxidation numbers add together to get zero, the formula is a one-to-one ratio of the elements.


Example: potassium fluoride

K1+

F1-

KF


Example: aluminum sulfide

Al3+

S2-


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.



Al3+

S2-

3+2-


Omit all positive and negative signs and omit all 1’s.



Al S2 3

Al2S3

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.

NaNO3Sodium nitrate

CaSO4Calcium 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.


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.


Example: potassium nitrate

K1+

NO3

1-


If the two oxidation numbers add together to get zero, the formula is a one-to-one ratio of the elements.


Example: potassium nitrate

K1+

NO3

1-KNO3


Example: aluminum sulfate

Al3+

SO4

2-


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.



Al3+

SO4

2-

3+2-( )


Omit all positive and negative signs and omit all 1’s.



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

Objectives l PSc.2.2.3 –Predict chemical formulas and names for simple compounds based on...

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