Compounds

A compound is a pure substance that contains two or more elements that are chemically bonded to each other

Compounds form when the electrons of two or more elements interact and are composed of either:Molecules

Ions

HO

Hwater =

Salt = NaCl Na , Cl

Molecules

Molecule:A group of atoms combined in

definite proportions and held together by strong attractive forces called covalent chemical bonds Covalent bonds are formed when

atoms share two or more electrons.

The smallest representative particle of a molecular compound

Molecular Compounds

Molecular compoundscomposed of molecules that contain

more than one type of atom

Most molecular substances are composed of non-metals only.

Examples:Water (H2O)Ethyl alcohol (C2H6O)Carbon dioxide (CO2)Ammonia (NH3)

Ionic Compounds

Ionic compounds are composed of ions (both cations and anions) and usually contain a metal and one or more nonmetals.

“Salt” (NaCl) Contains Na+ and Cl- ions

Tums (CaCO3) Contains Ca2+ and CO3

2- ions

Milk of Magnesia [Mg(OH)2] Contains Mg2+ and OH-

Ionic Compounds

Ionic compounds such as NaCl are formed whenone or more electrons are transferred

from one atom to another

the resulting cation and anion are strongly attracted to each other and are held together by an ionic bond resulting from electrostatic forces of attraction

Chemical Formulas

The composition of a compound is generally shown using a chemical formula:A shorthand notation that describes

the types and relative (or exact) numbers of each atom (or ion) present in a pure substance

Chemical formulas always contain:Elemental symbolsSubscripts

Show the relative (or exact) number of each type of atom or ion

Chemical Formulas

Molecular Formula chemical formula that tells the actual

number of each type of atom in a molecule

Empirical Formulachemical formula that tells the smallest

whole number ratio of each type of atom in a molecule

Acetic Acid C2H4O2 CH2OAscorbic Acid C6H8O6 C3H4O3

Sodium Sulfate Na2SO4

Ionic Compounds

The ions present in an ionic compound can be either:MonoatomicPolyatomic

Monoatomic ion:a charged species containing a

single atom that has gained or lost electrons Al3+

S2-

Predicting Ion Charge – Monoatomic Ions Many atoms gain or lose electrons in

such a way that they end up with the same number of electrons as the nearest (closest in atomic number) noble gas.“octet” rule

Ca (20p, 20e-) Ca2+ (20p, 18e-) [Ar: 18p,18e-]

O (8p, 8e-) O2- (8p, 10e-) [Ne: 10p, 10e-]

Predicting Ion Charge – Monoatomic Ions Using the octet rule you can easily

determine the charge on most of the monoatomic ions formed by the main group elements.

Main group metal cations: Charge = group number

Main group nonmetal anions: Charge = group # - 8

(or simply count the number of “spaces” away from the nearest noble gas and add a negative sign)

Common Monoatomic Ions

In general:Metal atoms and hydrogen lose e- and form cations.Nonmetal atoms gain e- and form anions.

Know These!

Zn2+

Ag+

P3-

Common Monoatomic Ions

Many transition metals and a few main group elements form more than one ion.

Mai

n gr

oup

Fe2+

Fe3+

Cu+

Cu2+

Mn2+

Mn3+

Co2+

Co3+

Bi3+

Bi5+

Cr2+

Cr3+

Sn2+

Sn4+

Pb2+

Pb4+

Main group

Names of Monoatomic Ions - Cations Cations formed by a metal have the

same name as the metal.K+ potassium ionCa2+ calcium ionAl3+ aluminum ion

If a metal forms more than one cation, use Roman numerals in ( ) after the name of the metal to show its charge.

Fe2+ iron (II) ionFe3+ iron (III) ionCu+ copper (I) ionCu2+ copper (II) ion

Names of Monoatomic Ions - Anions Monoatomic anions are named by:

dropping the ending of the element’s name

adding “ide”

N nitrogen O oxygen

N3- O2-nitride oxide

Polyatomic Ions

Polyatomic ion: an electrically charged group of two

or more atoms that are held together by covalent bonds Polyatomic ions cannot be broken

into smaller pieces.

Examples: NO3

-

SO42-

HCO3-

PO43-

NH

H

H

H

Polyatomic Ions

You are responsible for knowing the names and formulas of all ions listed in your syllabus, including the common polyatomic ions: Ammonium NH4

+

Hydroxide OH-

Cyanide CN-

Nitrate NO3-

AcetateC2H3O2

-

Sulfate SO42-

Bisulfate (Hydrogen sulfate) HSO4-

Carbonate CO32-

Bicarbonate (Hydrogen carbonate) HCO3-

Phosphate PO43-

Naming Oxyanions

Many of the polyatomic anions are oxyanions. polyatomic anions containing one or more

oxygens attached to a central atom To name an oxyanion, drop the ending of

the central atom name and add: “ate” most common oxyanion

of the element

“ite” 1 less oxygen

NO3- nitrate SO4

2- sulfateNO2

- nitrite SO32- sulfite

CO32- carbonate PO4

3- phosphatePO3

3- phosphite

XOnm-

Oxyanions

Nob

le

gases

3A

4A

5A

6A

7A

NO3-

nitrateCO3

2-

carbonate

ClO3-

chlorate

BrO3-

bromate

IO3-

iodate

PO43-

phosphate

SO42-

sulfate

“ate” oxyanions to memorize

Oxyanions

The halogens typically form 4 different oxyanions:

“per” 1 more O than the “ate” oxyanion

“hypo” 1 less O than the “ite” oxyanion

ClO4- perchlorate most oxygens

ClO3- chlorate most common

ClO2- chlorite 1 less O

ClO- hypochlorite fewest oxygens

Oxyanions

Anions derived by adding one or two H+ to an oxyanion:

add “hydrogen” or “dihydrogen” as prefix to oxyanion name

CO32- carbonate

HCO3- hydrogen carbonate

(usually called bicarbonate)

PO43- phosphate

H2PO4- dihydrogen phosphate

Writing Formulas for Ionic Compounds Ionic compounds are always

represented using an empirical formula with the cation shown first.

The formula for an ionic compound must be electrically neutral.Total positive charge = total

negative charge

Although ions are present in an ionic compound, the formula does NOT explicitly show the charge of the ions.

NaCl not Na Cl

Writing Formulas for Ionic Compounds Ionic compounds must be electrically

neutral.Total positive charge = total

negative charge

Na+ + Cl- NaCl (1 pos, 1 neg)

Na++Na++ Cl-

Writing Formulas for Ionic CompoundsCa2+ + Cl- CaCl (2 pos, 1 neg)

Ca2+Cl-

Ca2+ + 2Cl- CaCl2 (2 pos, 2 neg)

Ca2+Cl-

Cl-

Writing Formulas for Ionic Compounds To write the empirical formula of an

ionic compound from its name:

1. Identify the formula including charge for each ion.

2. Combine the ions in a ratio that gives an electrically neutral compound.

Writing Formulas for Ionic Compounds If charges on the ions are equal in

magnitude (but opposite in sign), then combine the ions in a 1:1 ratio.

Ca2+ SO42-

sodium bicarbonate

Na+ HCO3-

NaHCO3

calcium sulfate

Ca2+ SO42-

CaSO4

HCO3-Na+

Writing Formulas for Ionic Compounds If charges on the ions are different, then

flip-flop the charges (i.e. the charge of one ion becomes the subscript of the other ion).

Place ( ) around a polyatomic ion IF more than one is needed.

magnesium nitride calcium hydroxide

Ca2+ OH 1-

Ca(OH)2

Writing Formulas for Ionic CompoundsExample: Write the correct formula for the following ionic compounds.

Zinc bromide

Aluminum carbonate

Iron (II) phosphate

Tin (IV) sulfate

Magnesium hydroxide

Writing Formulas for Ionic CompoundsExample: Write the correct formula for the following ionic compounds.

Sodium bicarbonate

Ammonium sulfate

Potassium phosphite

Sodium hypochlorite

Copper (I) oxide

Writing Formulas for Ionic Compounds Remember:

Use empirical formulas

Formulas must be electrically neutral

Do not show the charges of each ion in the final formula that you write

Use parentheses around polyatomic ions if more than one is present in the formula Do not use ( ) around monoatomic ions Do not use ( ) around a single

polyatomic ion

Naming Ionic Compounds

Ionic compounds are named using the cation name followed by the anion name

CaBr2 calcium bromideNaClO sodium hypochloriteMg3(PO4)2 magnesium phosphate

If the cation can form ions with more than one charge, you must specify the charge:

Fe2S3 iron (III) sulfidePbO2 lead (IV) oxide

Naming Ionic Compounds

Example: Name the following ionic compounds.

Na2SO4

FeCl3

(NH4)3PO4

KClO4

Cu2CO3

Sn(SO4)2

Common “Household” Chemicals You are responsible for knowing the

names and formulas for the chemical present in:Baking soda

sodium bicarbonate NaHCO3

Table salt Sodium chloride NaCl

Bleach Sodium hypochlorite NaClO or NaOCl