Chapter 3

Molecules, Compounds, and

Chemical Composition

Elements and Compounds

Elements combine together to make an almost limitless number of compounds.

The properties of the compound are totally different

from the constituent elements.

Compounds ≠ Mixtures

Hydrogen gas b.p. -253º

Oxygen gas b.p. -183º

Water b.p. 100º

Hydrogen peroxide b.p. 150º

Hydrogen and Oxygen gases can mix in any ratio.

Hydrogen and Oxygen atoms

present in fixed ratios

Chemical Bonds

Compounds are made of atoms held together by bonds.

Chemical bonds are forces of attraction between atoms.

The bonding attraction comes from attractions between protons and electrons.

Bond TypesTwo general types of bonding between atoms found in

compounds, ionic and covalent.

Ionic bonds result when electrons have been transferred

between atoms, resulting in oppositely charged ions that

attract each other.

Generally found when metal atoms bond to nonmetal atoms

Covalent bonds result when two atoms share some

of their electrons.

Generally found when nonmetal atoms bond

together

Formation of an Ionic Compound

}Na0

Cl0

⤸Neutral Atoms Undergo

Electron Transfer

Na+Cl-

Charged Ions

An Orderly Aggregate Called an Ionic Crystal

repulsive forces

attractive force

attractive force

Formation of an Covalent Compound Involves Competing Forces

nucleus

electron cloud

The total energy of the atoms is a combination of the attractive and repulsive forces

Ener

gy

Internuclear distance

74 pm

Chemical Formulas Describe Compounds

A compound is a distinct substance that is composed of atoms of two or more elements.

We describe the compound by describing the number and type of each atom in the simplest unit of the compound.

Each element is represented by its letter symbol.

The number of atoms of each element is written to the right of the element as a subscript.

Polyatomic ions are placed in parentheses.

(if more than one is present)

Types of Formulas: Empirical FormulaAn empirical formula gives the relative number of atoms of each element in a compound.

It does not describe how many atoms, the order of attachment, or the shape.

For example:

1) The empirical formula for the ionic compound fluorspar is CaCl2. This means that there is 1 Ca2+ ion for every 2 Cl− ions in the compound.

2) The empirical formula for the molecular compound oxalic acid is CHO2. This means that there is 1 C atom and 1 H atom for every 2 O atoms in the molecule.

Types of Formulas: Molecular Formula

A molecular formula gives the actual number of atoms of each element in a molecule of a compound.

It does not describe the order of attachment, or the shape.

The empirical formula for the molecular compound oxalic acid is CHO2.

The actual molecular formula is C2H2O4

Types of Formulas: Structural Formula

A structural formula uses lines to represent covalent bonds and shows how atoms in a molecule are connected or bonded to each other.

Structural Formulas of Oxalic Acid

O C

O

C

O

O HH

Molecular Models

Practice — Find the empirical formula for each of the following

The ionic compound that has two aluminum ions for every three oxide ions

arabinose, C5H10O5

pyrimidine

ethylene glycol

C

C

N

C

N

C

H

HH

H

Al2O3

CH2O

C2H2N

CH3O

}

C4H4N2

C2H6O2

ElementsMOST ELEMENTS

Single atoms are the constituent particles. The atoms may be physically attracted to each other, but

are not chemically bonded together.

A FEW ELEMENTS Molecules are the constituent particles.

The molecules are made of two or more atoms chemically bonded together by covalent bonds.

F2

Cl2

Br2

I2

H2

O2N2

Molecular Elements

S8 P4

Molecular Elements

Compounds

SOME COMPOUNDS Composed of ions arranged in a 3-dimensional pattern

These are called ionic compounds.

OTHER COMPOUNDS Composed of individual molecule units

Each molecule contains atoms of different elements chemically attached by covalent bonds

These are called molecular compounds.

Propane – contains individual C3H8

molecules

Table salt – contains an array of Na+ ions

and Cl- ions

Molecular vs. Ionic Compounds

Classify Each of the Following as Either an Atomic Element, Molecular Element, Molecular Compound, or

Ionic Compound

Aluminum, AlAluminum chloride, AlCl3Chlorine, Cl2Acetone, C3H6OCarbon monoxide, COCobalt, Co

atomic elementionic compound

molecular elementmolecular compound

molecular compoundatomic element

A compound must have no total charge, therefore we must balance the numbers of cations and

anions in a compound to get ø charge.

Practice — What are the formulas for compounds made from the following ions?

Potassium ion with a nitride ion

Calcium ion with a bromide ion

Aluminum ion with a sulfide ion

K3N

CaBr2

Al2S3

K+ with N3−

Ca2+ with Br−

Al3+ with S2−

calcium bromide

aluminum sulfide

potassium nitride

Chapter 3

Molecules, Compounds, and

Chemical Composition

Table of Representative Elements

Li Be B C N O F

Na Mg Al Si P S Cl

K Ca Ga Ge As Se Br

Rb Sr In Sn Sb Te I

He

Ne

Ar

Kr

Xe

H

IA

IIA IIIA IVA VA VIA VIIA

VIIIA(1)

(2) (13)

(18)

(17)(14) (15) (16)1

2

3

4

5

Periodic Table-Main Groups Only

Li Be B C N O F

Na Mg Al Si P S Cl

K Ca Ga Ge As Se Br

Rb Sr In Sn Sb Te I

He

Ne

Ar

Kr

Xe

H

Gain electrons

IA

IIA IIIA IVA VA VIA VIIA

VIIIA(1)

(2) (13)

(18)

(17)(14) (15) (16)

Lose electrons

1

2

3

4

5

B C N O F

Al Si P S Cl

Ga Ge As Se Br

In Sn Sb Te I

He

Ne

Ar

Kr

Xe

H

Gain electrons Lose electrons

H

Li Be B C N

Na Mg Al Si P

K Ca Ga Ge As

Rb Sr In Sn Sb

1

2

3

4

5

Cs Ba

1

2

3

4

5

6

C N3- O2- F-

Si P3- S2- Cl-

Ge As3- Se2- Br-

Sn Sb Te2- I-

He

Ne

Ar

Kr

Xe

H-

H+

Li+ Be2+ B C N

Na+ Mg2+ Al3+ Si P

K+ Ca2+ Ga3+ Ge As

Rb+ Sr2+ In3+ Sn Sb

1

2

3

4

5

Cs+ Ba2+

1

2

3

4

5

6

IA IIA IIIAVA VIA VIIA VIIIA

Main-group ions and the noble gas configurations.

Everyone Wants to Be Like a Noble Gas!

A compound must have no total charge. Therefore we must balance the numbers of cations

and anions in a compound to get zero charge.

Writing Formulas for Ionic Compounds

Remember !!!!

Metal atoms lose electrons to form cations.

Nonmetal atoms gain electrons to form anions.

The number of electrons lost or gained can be predicted from the elements position on the Periodic

Table.

Ne

Kr

Ar

Xe

Why is a particular number of electrons lost or gained ?

Na Cl nucleus

core electronsvalence electrons

Na+ Cl-

Na + Cl -Na Cl + +

Determining the Number of Valence Electrons in an Atom

The column number on the Periodic Table will tell you how many valence electrons a main group atom has.

Lewis Dot Structures of Atoms

We represent the valence electrons of main-group elements as dots surrounding the symbol for the element.

H

Li Be B C N O F Ne

He

Na Mg Al Si P S Cl Ar

B C N

P

IA

IIA IIIA

IVA VA VIA VIIA

VIIIA

The column number on the Periodic Table will tell you how many valence electrons a main group atom has.

Cl

CaCl2

Formation of Calcium Chloride

Ca

Cl

Ca 2+

Cl - Cl -

20p 20e

20p 18e

17p 17e 17p

18e

17p 17e

17p 18e

Practice – Write the Lewis structure for

Arsenic

A lithium ion A fluoride ion

•••

••

As

Stable Electron Arrangementsand Ion Charge

Metals form cations by losing electrons to get the same number of valence as the previous noble gas.

Nonmetals form anions by gaining electrons to get the same number of valence electrons as the next noble gas.

A noble gas electron configuration with eight valence electrons appears to be particularly stable.

Octet RuleWhen atoms bond, they tend to gain, lose, or share

electrons to result in eight valence electrons

ExceptionsH, Li, Be, B attain an electron configuration like He

He = two valence electrons (a duet) Li loses its one valence electron H may share or gain one electron

It commonly loses its one electron to become H+ Be loses two electrons to become Be2+

It commonly shares its two electrons in covalent bonds, resulting in four valence electrons

B loses three electrons to become B3+

It commonly shares its three electrons in covalent bonds, resulting in six valence electrons

Expanded octets for elements in Period 3 or below

Na +Na

O

Cl - NaCl

Cl

CaCl2

Ca

Ca 2+

Cl

Cl - Cl -

Na

Cl

Na

O 2-Na +Na +

Na2O

Dot structures can illustrate the process.

sodium chloride

calcium chloride

sodium oxide

Al2O3

Formation of Aluminum Oxide

O

O 2-

AlAl

O

O

Al3+ Al3+

O 2-

O 2-

Write a formula for the ionic compound that forms from aluminum and oxygen.

Al3+ O2-

Al2O3

Write a formula for the ionic compound that forms from magnesium and oxygen.

MgO

Mg2+ O2-

Mg2O2

Chapter 3

Nomenclature of Inorganic Compounds

What type of compound is it ?

Ionic Compound Covalent (Nonionic) Compound

Acid

Cation with fixed charge

Cation with variable charge

Binary Contains polyatomic ion Binary Contains

polyatomic ion

Binary Acid

Oxy Acid

Aluminum, AlChlorine, Cl2 Aluminum chloride, AlCl3Iron (II) chloride, FeCl2Sodium Phosphate, Na3PO4Tin (IV) Chloride SnCl4Carbon monoxide, COCarbon dioxide, CO2Hydrochloric Acid, HClPerchloric Acid, HClO4

atomic element

ionic compoundmolecular element

molecular compound

ionic compoundionic compound

ionic compound

molecular compoundbinary acidoxy acid

What type of compound is it ?Practice:

Binary Ionic Compounds

Naming Metal Cations

Some metals form cations having only one possible charge

IA , IIA , Al , Ag , Zn , Sc IA+, IIA2+, Al3+, Ag1+, Zn2+, Sc3+

name of cation = name of metal

Naming Metal Cations

Most metals can form cations with more than one possible charge.

The charge must be determine from the charge on the anion.

name of cation = name of metal with Roman numeral charge in parentheses

IVA VA VIA VIIA

H -

hydride

C4-

carbideN3-

nitrideO2-

oxideF -

fluoride

Si4-

silicideP3-

phosphideS2-

sulfideCl -

chloride

As3-

arsenideSe2-

SelenideBr -

bromide

Te2-

TellurideI -

iodide

Naming Monatomic Nonmetal AnionsDetermine the charge from position on the Periodic Table.

To name anion, change ending on the element name to –ide.

C22-

Si?-

As?-

XX

X

Naming Binary Ionic Compounds for Metals with Invariant Charge

1. Name the metal cation first, name nonmetal anion second

2. Cation name is the metal name

3. Nonmetal anion named by changing the ending on the nonmetal name to -ide

name of cation(metal)

base name of anion (nonmetal) “ide”+ +

1. KCl

2. MgBr2

3. Al2S3

potassium chloride

magnesium bromide

aluminum sulfide

name of cation(metal)

base name of anion (nonmetal) “ide”+ +

Name the following compounds

Naming Binary Ionic Compounds for Metals with Variable Charge

1. Name metal cation first, name nonmetal anion second

2. The metal cation name is the metal name followed by a Roman numeral in parentheses to indicate its charge determine charge from anion charge.

3. Nonmetal anion named by changing the ending on the nonmetal name to -ide

name of cation(metal)

base name of anion (nonmetal) “ide”+( )+ +charge of cation (metal) in

roman numerals

Determine a charge from the formula of a specific compound.

The sum of all the charges must be zero.

Example: The charge on iron (Fe) in FeCl3 must be 3+ in order for the compound to be charge neutral with

the three Cl- anions.

name of cation(metal)

base name of anion (nonmetal) “ide”+( )+ +charge of cation (metal) in

roman numerals

Name the following compounds

1. CuF2 2. TiCl4 3. PbBr2

4. CrO3

5. Fe3N2

6. Fe2S3

Charge on Cation?Cu= 2+

Ti = 4+

Pb = 2+

Cr = 6+Fe = 2+Fe= 3+

copper (II) fluoride

titanium (IV) chloride

lead (II) bromide

chromium (VI) oxideiron (II) nitrideiron (III) sulfide

Na +Na

Cl - NaCl

ClFeCl2

Fe

Fe 2+

Cl

Cl - Cl -

Cl

Fe 3+FeCl3

Using dot structures can illustrate the formation of binary ionic compounds.

sodium chloride

iron (II) chloride

iron (III) chloride

ClFe

Cl

Cl

Cl -

Cl -Cl -

O

FeOFe

Fe 2+

Na

Na

O 2-Na +Na +

Na2O

Using dot structures can illustrate the formation of binary ionic compounds.

sodium oxide

iron (II) oxide

iron (III) oxide

O O 2-

Fe Fe

O O O

Fe 3+

Fe 3+

O 2-

O 2-O 2- Fe2O3

Compounds Containing Polyatomic Ions

Polyatomic ions are ions that contain more than one atom.

Often identified by parentheses around ion in formula

Name and charge of polyatomic ion do not change

An ionic compound is always named by naming the cation first and then the anion.

+3 +4 +5 +6 +7

BO33-

borateCO32-

carbonateNO3-

nitrate

SiO32-

silicatePO43-

phosphateSO42-

sulfateClO3-

chorate

AsO43-

arsenateSeO42-

selenateBrO3-

bromate

TeO42-

tellurateIO3-

iodate

Periodic Pattern of Polyatomic Ions-“ate” groups

“formal charge” on central atom

Some Common Polyatomic Ions

Name the Following Compounds

1. Na2SO4

2. Fe(NO3)3

3. NH4Cl

4. Ca(C2H3O2)2

5. Cu(NO3)2

sodium sulfate

iron (III)nitrate

ammonium chloridecalcium acetate

copper(II) nitrate

SO42-, sulfate; NO3 -, nitrate;

NH4 +, ammonium; (C2H3O2) -, acetate

Writing formula for ionic compounds containing polyatomic ions

Aluminum sulfate

Iron (III) phosphate

Chromium (II) hydrogen carbonate

Al2(SO4)3

FePO4

Cr(HCO3)2

SO42-, sulfate; PO4 3-, phosphate;

(HCO3) -, hydrogen carbonate

Hydrates

Hydrates are ionic compounds containing a specific number of waters for

each formula unit.

In formula, attached waters indicated

CoCl2·6H2O or CoCl2(H2O)6

In name attached waters indicated by prefix+hydrate

after name of ionic compound:

CoCl2·6H2O cobalt(II) chloride hexahydrate

CaSO4·½H2O calcium sulfate hemihydrate

Writing Names of Binary Molecular Compounds of Two Nonmetals

1. Write name of first element in formulaa) element furthest left and down on the Periodic Table b) use the full name of the element

2. Write name the second element in the formula with an -ide suffix, as if it were an anion; however, remember these compounds do not contain ions!

3. Use a prefix in front of each name to indicate the number of atoms (Never use the prefix mono- on the first element)

BF3

NO2

PCl5

I2F7

Formulas --------------> Names

boron trifluoride

nitrogen dioxide

phosphorous pentafluoride

diiodine heptafluoride

prefix prefix “ide”name of first element

name of second element+ + + +

Name -------------> Formula

dinitrogen pentoxide

dinitrogen tetroxide

sulfur hexafluoride

diarsenic trisulfide

N2O5

N2O4

SF6

As2S3

prefix prefix “ide”name of first element

name of second element+ + + +

Acids

Acids are molecular compounds that form H+ when dissolved in water.

(aq) is often written after the formula

Sour taste

Dissolve many metals such as Zn, Fe, Mg; but not Au, Ag, Pt

Formula generally starts with H e.g., HCl, H2SO4

Acids

Binary Acidscontain only two elements

Oxyacidscontain oxygen

Naming Binary Acids

HCl HF HI

hydrochloric acid

base name of nonmetal“hydro” “ic” acid+ + +

hydrofluoric acidhydroiodic acid

Naming OxyacidsName the polyatomic anion !!!!!

If polyatomic ion name ends in –ate,

base name of oxyanion

“ic” acid

If polyatomic ion name ends in –ite,

base name of oxyanion

“ous” acid

+ +

+ +

Oxyanion formula Oxyanion name Acid Formula Acid Name

NO2 ⊖ nitrite H+ HNO2 nitrous

NO3 ⊖ nitrate H+ HNO3 nitric

SO3 2⊖ sulfite 2H+ H2SO3 sulfurous

SO4 2⊖ sulfate 2H+ H2SO4 sulfuric

ClO2 ⊖ chlorite H+ HClO2 chlorous

ClO3 ⊖ chlorate H+ HClO3 chloric

C2H3O2 ⊖ acetate H+ HC2H3O2 acetic

CO3 2⊖ carbonate 2H+ H2CO3 carbonic

Names of Common Oxyacids and Their Oxyanions

H2SO4 sulfuric acidH2SO3 sulfurous acid

HClO hypochlorous acidHClO2 chlorous acidHClO3 chloric acidHClO4 perchloric acid

“-ate” = “-ic” ; “-ite” = “-ous”

Naming Oxyacids

Formula ----------> Name

H2S

HClO3

HNO2

hydrosulfuric acid

chloric acid

nitrous acid

ClO3-, chlorate; NO2-, nitrite

chlorous acid

phosphoric acid

hydrobromic acid

Name ----------> Formula

HClO2

H3PO4

HBr

ClO2-, chlorite; PO4 3-, phosphate