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Naming and Formula Writing for Ionic and Covalent Compounds

Naming and Formula Writing for Ionic and Covalent Compounds

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Objectives… List differences among ionic and

covalently bonded compounds Identify polyatomic and monatomic

ions and name them properly Write the chemical formulas and

names for ionic compounds Write the chemical names and

formulas of acids Write the chemical names and

formulas of molecules

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Review of Ionic Compounds (Crystals)

Transfer of electrons Made from a metal and a non-metal Metals lose electrons, nonmetals gain

electrons Chemical formula is arranged in the

smallest whole number ratio (empirical formula) Formula unit: the smallest repeating pattern

within a crystal

Even though ionic compounds are made up of ions, they ARE ELECTRICALLY NEUTRAL!

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Ions can be monatomic or polyatomic: Monatomic: Made up of a single atom Polyatomic: Made up of multiple atoms

Remember…Group #: 1 2 13 14 15 16 17 18Charge: +1 +2 +3 X -3 -2 -1 X

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Monatomic cations have the same name as the element Example: Na+1 = Sodium ion, Ca+2 =

Calcium ion

Monatomic anions have the ending of the element name changed to“-ide” Example: Cl-1=chloride ion, O-

2=oxide ion

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Polyatomic ions: (See polyatomic ion sheet) are

made up of two or more elements

covalently bonded together with an overall

positive or negative charge.

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Review Molecular Compounds (Molecules)

Sharing of electrons Made from nonmetals only Molecules of the same compound are

IDENTICAL and INDEPENDENT of each other

Chemical formula indicates the exact makeup of one molecule (molecular formula)

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Rules for Formula Writing (Ionic Compounds)

Since all compounds are neutral, figure out how many of each ion is needed to make a neutral compound. (Neutral means having a net zero charge.)

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Examples

Mg and ClMg+2 Cl-1

Cl-1

Al and OAl+3 O-2

Al+3 O-2

O-2

MgCl2

Al2O3

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More Examples

Ca and SCa+2 S-2

Ca and (AsO4)

Ca+2 (AsO4)-3

Ca+2 (AsO4)-3

Ca+2

CaS

Ca3(AsO4)2

Parentheses are needed if there is more than one of the polyatomic ions!

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Aluminum SulfiteAl+3 (SO3)-2

Al+3 (SO3)-2

(SO3)-2

Chemical Name to Formula

Al2(SO3)3

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More Examples

Silver SulfateAg? (SO4)-2

Ag+1

Ag2(SO4)Ag+1

Use your Periodic Table to determine the charge

on transition metals!

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More Examples

Nickel (II) NitrateNi+2 (NO3)-1

(NO3)-1 Ni(NO3)2

The Roman Numeral will always tell you the charge and it will always be positive

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More Examples

Iron (III) ChlorideFe+3 Cl-1

Cl-1

Cl-1FeCl3

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Chemical Formula to NameRecall the format for chemical formulas…

(name of cation – metal) (name of anion – nonmetal)

Examples:KBr

CaI2

Na(SO4)

Potassium Bromide

Calcium Iodide

Sodium Sulfate

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For elements with more than one possible charge (transition metals)

…Use the charge on the anion to determine the charge on the

cation!Example:

Fe2(CrO4)3

-2(3)=-6+6/2=+3

Iron (III) Chromate

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Example:Sn(CO3)2

-2(2)=-4+4

Tin (IV) Carbonate

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Example:Cu3P

-3+3/3=+1

Copper (I) Phosphide

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Criss Cross Short Hand MethodJust use the number of the charge (not the charge itself) and criss cross as shown

below. You will note that the overall charge is neutral, as the total positive charge of the metals offsets the total negative charge of the nonmetal.

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Naming Acids

Acids are ionic compounds that contain H+1 as their cation.

Acids are named based on their anion.

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If the anion ends in…

“-ide” hydro ___ ic acid

Example: H2S

Hydrosulfuric acid

Sulfide (S-2) is the anion!

The root name of the anion goes here

(remove-ide)

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If the anion ends in…

“-ate” ___ ic acid

Example: H2SO4

Sulfuric acid

Sulfate (SO4-2) is the

anion!

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If the anion ends in…

“-ite” ___ ous acid

Example: H2SO3

Sulfurous acid

Sulfite (SO3-2) is the anion!

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Mnemonic devices to help you remember Acid Nomenclatire

#1) “eight is great”er number of oxygens

“ite” is slight” less number of oxygens

#2) Chemistry “Diseases” (joke..I am suffering from eight-ic-ite-ous or)....

“ate” -ic “ite”-ous

SO4 = sulfate SO3 = sulfite

H2SO4 H2SO3

Sulfuric Acid Sulfurous Acid

or

lessous icmore

NO2 = nitrite NO3 = nitrate

HNO2 nitrous acid HNO3 nitric acid

PO3 = phosphite PO4 = phosphate

H3PO3= phoshporous Acid H3PO4 = phosphoric Acid

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Formula Writing

Use the reverse to determine the anion and balance out the

charges for a neutral compound.

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Examples

Hydrophosphoric acid

H+1 P-3

H+1

H+1

All acids contain a H+1 charge as the cation!

Ask yourself, “What was the original

ending?”H3P

Original ending “ide”

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Examples

Chromic acid

H+1 (CrO4)-2

H+1

Original ending “ate”

H2CrO4

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Naming Molecular Compounds

Recall, covalently bonded molecules are made up of

nonmetals only.

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Prefixes

mono – 1 hexa – 6di – 2 hepta – 7tri – 3 octa – 8tetra – 4 nona –

9penta – 5 deca -

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Must be memorized!

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RulesUse the prefixes to indicate how many of each element is in one molecule.Change the ending on the second element to “-ide”

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ExamplesN2O4

CO

SiO2

If there is only one of the first element, do not write mono.

dinitrogen tetraoxide

carbon monoxide

silicon dioxide

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Formula WritingUse the prefixes to determine the subscripts

Examples: trisulfur hexafluoride

carbon pentaoxide

tetraphosphrous dioxide

S3F6

DO NOT REDUCE!

CO5

P4O2