Chemistry 068, Chapter 5

Compounds and Nomenclature

• Most substances are compounds rather than elements.

• Compounds are substances formed from more than one element.

• Nomenclature is the system used to name chemical compounds.

Molecules

• Lone atoms are fairly rare – most matter is made up of multiple atoms acting together.

• A group of two or more atoms, tightly bonded together, that functions as a single unit is called a molecule.

• Aggregates of many molecules can be either ionic (held together by positive and negative charged atoms strongly held together in a lattice) or molecular (lots of molecules weakly held together).

Classifying Molecules

• Molecules can be homonuclear or heteronuclear.– Homonuclear, or homoatomic, molecules consist of

only one type of atom. These can still be called elements.

– Heteronuclear, or heteroatomic, molecules consist of more than one type of atom. These are compounds.

• The number of atoms in the molecule leads to the molecule being called diatomic (2 atoms), triatomic (3 atoms), tetratomic (4 atoms), and so forth.

Chemical Formulas

• A chemical formula is a representation of the number of and types of elements present in a compound.– It is very important to strictly follow the rules for writing chemical

symbols in chemical formulas.– CO (one carbon and one oxygen) is not the same as Co (one

cobalt).• Subscripts on atoms indicate the number of atoms of

each type in the molecule.– Atoms in parenthesis indicate sub-units in the molecules. A

subscript on the parenthesis is multiplied times all of the atoms in the parenthesis to indicate the number of atoms.

Chemical Formulas (Cont’d)

• All portions of a compound will have this constant ratio of atoms.– This is the law of constant composition.

• The meaning of the chemical formula varies slightly between ionic and molecular compounds.– In ionic compounds, the formula gives the ratio of the atom in the

compound.– In molecular compounds, the formula gives the ratio of the

atoms in the individual molecules making up the compound.

Chemical Formula Problems

• How many of each type of atom are in each of the following compounds?– CO2

– O2

– (NH4)2O

Chemical Formula Problems (Cont’d)

• Use the given information to write a formula for each of the following compounds.– Three carbons and eight hydrogens.

– Two hydrogens and one oxygen.

– One carbon and four hydrogens.

Types of Chemical Formulas

• An empirical formula gives the simplest whole number ratio of atoms.

• A molecular formula gives actual number of atoms in the molecule.

• For example CH is an empirical formula, C6H6 is a molecular formula.

• A structural formula uses lines to show how a molecule is put together. (More on these is a later chapter).

Molecular View

• Elements can be split into two categories.– Atomic elements exist as single atoms.– Molecular elements do not normally exist in

nature as single atoms.

• Compounds are typically either molecular or ionic.– Molecular compounds are formed by two or

more nonmetals.– Ionic compounds are formed by metals and

nonmetals or polyatomic ions bonding.

Predicting Ionic Charge

• It is possible to predict ionic charge from the position of an element on the periodic table.

• The first two groups will form positive ions equal to their group #.

• The charge on transition metals cannot be easily predicted.

• The charge on the last group (noble gasses) is zero.• The next three groups will be -1 each group left of the

noble gasses.• The remaining two groups are harder to predict as they

can be positive or negatively charged.

Predicting Ionic Charge Problems

• Predict the charge of ions formed from the following atoms.

– Na

– Al

– P

– Cl

– Ar

Isoelectronic Species

• Isoelectronic species have the same number of electrons.

• This does NOT mean they have the same properties, they are only alike in the number of electrons they posses.

Ionic Compound Formulas

• Ionic compounds are molecules formed by combining two ions.– Either single or polyatomic ions.

• The cation is always listed first in the formula.• The charges on individual ions is not shown.• Formulas must have a net charge of zero.• Ratios of the ions must create a zero net charge – you

must have as many positive charges as negative charges.

• For example:– NaCl is formed from Na+ and Cl-

– CaBr2 is formed from Ca2+ and Br-

Typical Ionic Formulas

Anions (X)

Cation (M) - -2 -3 -4

+ MX M2X M3X M4X

+2 MX2 MX M3X2 M2X

+3 MX3 M2X3 MXM4X3

+4 MX4 MX2 M3X4 MX

Ionic Compound Problems

• Determine the empirical formulas for the ionic compounds formed by combining the following:– Mg2+ and F-

– Fe3+ and O2-

– Be2+ and S2-

Polyatomic Ions

• Polyatomic ions consist of a group of atoms, held together by covalent bonds, which are held together due to the loss or gain of electrons.

• The entire polyatomic group works the same way as a single ion when determining formulas.

• It is important to realize that polyatomic ions are not true molecules, they are pieces of compounds and not compounds themselves.

Ionic Compound Problems

• Determine the empirical formulas for the ionic compounds formed by combining the following:– Mg2+ and OH-

– NH4+ and O2-

– Na+ and NO3-

Nomenclature

• Nomenclature is the system used to name chemical compounds.– The system has been adopted by the IUPAC.

• There are separate rules for different types of molecules.

• Most of these rules apply to binary compounds.– Binary compounds are those consisting of

only two elements.

Classification of Compounds for Nomenclature

• For nomenclature purposes, molecules are broken down into several categories:– Elements.– Ions and ionic compounds.

• For nomenclature purposes, and compound of a metal and nonmetal are considered ionic as are compounds containing one or more polyatomic ions.

– Binary molecular compounds.• Again, for nomenclature purposes, these only include

compounds of nonmetals and nonmetals.• Metalloids are usually named using molecular nomenclature.

– Acids.

Nomenclature – Elements

• Naming elements is simple – you just use the name off of the periodic table.

• In the case of elements that normally exist as diatomic molecules, rather than single atoms, you still use the element name. – They are sometimes indicated as diatomic

element or molecular element to differentiate them from a single atom.

– This specifically applies to H2, N2, O2, F2, Cl2, Br2, and I2

Nomenclature – Elements Examples

• Fe

• N2

• Sn

Binary Ionic Compounds

• Binary ionic compounds contain a metal and a nonmetal.

• Binary ionic compounds are contain either fixed charge or variable charge metal ions.– The naming rules are slightly different for

each.

Fixed vs. Variable Charge Metal Ions

• Fixed charge metal ions can only have one possible charge.– There are only 15 fixed charge elements.– They are: Li+, Na+, K+, Rb+, Cs+, Ag+, Be2+,

Mg2+, Ca2+,Sr2+,Ba2+, Zn2+, Cd2+, Al3+, Ga3+.

• Variable charge metal ions can have different charges.– Each charge has a separate name, so Fe2+

has a different name than Fe3+.– All metals, other than the 15 above, are

variable charge.

Positive Ion Nomenclature

• Positive ions are simply called metal ion, unless there is more than one possible positive ion (variable charged).

• Polyatomic ions each have their own name.

• Fixed charge metals are thus:– Note that the particular charge does not

matter.– So Na+ is called sodium ion.– Mg2+ is called magnesium ion.

Positive Ion Nomenclature (Cont’d)

• In the case of variable charge metals they are named metal (charge) ion with the charge in roman numerals.– In this case, charge does matter, as you must denote

which charge it has.– Cu+ is thus copper (I) ion.– Cu2+ is thus copper (II) ion.

• For variable charge metals, there is also an older method which uses ous suffix for smaller charge and ic for larger charge.– Cu+ is thus cuprous ion.– Cu2+ is thus cupric ion.

Common Variable Charge Metal Ions

Element Ions Old Root Name

Chromium (Cr) +2, +3 Chrom-

Cobalt (Co) +2, +3 Cobalt-

Copper (Cu) +1, +2 Cupr-

Gold (Au) +1, +3 Aur-

Iron (Fe) +2, +3 Ferr-

Lead (Pb) +2, +4 Plumb-

Manganese (Mn) +2, +3 Mangan-

Tin (Sn) +2, +4 Stann-

Mercury (Hg) Hg22+; Hg2+ Mercur-

Negative Ion Nomenclature

• Polyatomic ions each have their own name.

• Single atom negative ions consist of a stem which denotes the particular ion and end in ide.

Common Negative Ions

Element Ion Stem NameBromine (Br) -1 Brom-Carbon (C) -4 Carb-Chlorine (Cl) -1 Chlor-Fluorine (F) -1 Fluor-Hydrogen (H) -1 Hydr-Iodine (I) -1 Iod-Nitrogen (N) -3 Nitr-Oxygen (O) -2 Ox-Phosphorous (P) -3 Phosph-Sulfur (S) -2 Sulf-

Ion Nomenclature Problems

• Name each of the following ions.

• Ag+

• Fe2+

• Fe3+

• Cl-

• O2-

Ion Nomenclature Problems (Cont’d)

• Write formulas for each of the following ions.

• Bromide ion.

• Stannic ion.

• Manganese (III) ion.

• Hydrogen ion.

• Lithium ion.

Binary Ionic Compound Nomenclature

• Ionic compound names consist of two words.• The first is the name of the metal. The word ion is

excluded.– In the case of variable charge metals the charge is indicated by

a roman numeral in parenthesis or by the old systematic names (-ic and –ous).

• The second is the name of the nonmetal ion, dropping the word ion.

• Note that the number of each ion is not a part of the name – it is inferred from the ions that form the compound.– Thus you must be able to determine the formula of an ionic

compound from the name and the type of ions in it.• Thus, NaCl is called sodium chloride.• Thus, FeCl2 is called iron (II) chloride or ferrous chloride.

Binary Ionic Compound Nomenclature Problems

• Name each of the following compounds.

• AgCl

• CaBr2

• FeO

• Fe2O3

• K3N

Binary Ionic Compound Nomenclature Problems (Cont’d)

• Write formulas for each of the following compounds.

• Potassium bromide.

• Stannic chloride.

• Manganese (III)nitride.

• Sodium carbide.

• Silver fluoride.

Nomenclature of Polyatomic Ions

• There are hundreds of polyatomic ions and each one has its own name.

• There is no easy way to learn the polyatomic ions.– Memorization is required.– There are very few patterns.

• The halogens follow the same names and charges.– The only thing that changes is the halogen stem name.

• There is a general pattern for the oxygen containing ions:– Lowest # Oxygens to greatest follows:– One to four oxygens: hypo-ite, -ite, -ate, per-ate– Only two possible: -ite, -ate

• Thio- compounds replace an oxygen with a sulfur.– OCN- is cyanate ion, SCN- is thiocyanate.

Common Polyatomic IonsElement Formula NameNitrogen NO3

- Nitrate ionNO2

- Nitrite ionNH4

+ Ammonium ionN3

- Azide ionSulfur SO4

2- Sulfate ionHSO4

- Hydrogen sulfate ion (bisulfate ion)SO3

2- Sulfite ionHSO3

- Hydrogen sulfite ion (bisulfite ion)S2O3

2- Thiosulfate ionPhosphorus PO4

3- Phosphate ionHPO4

2- Hydrogen phosphate ionH2PO4

- Dihydrogen phosphate ionPO3

3- Phosphite ion

Common Polyatomic Ions (Cont’d)

Element Formula NameCarbon CO3

2- Carbonate ionHCO3

- Hydrogen carbonate ion (bicarbonate ion)

C2O42- Oxalate ion

*C2H3O2- Acetate ion

CN- Cyanide ionOCN- Cyanate ionSCN- Thiocyanate ion

Chlorine** ClO4- Perchlorate ion

ClO3- Chlorate ion

ClO2- Chlorite ion

ClO- Hypochlorite ion

*Sometimes written CH3COO-

**All of the halogens follow the same pattern.

Common Polyatomic Ions (Cont’d)

Element Formula Name

Oxygen O22- Peroxide ion

Boron BO33- Borate ion

Hydrogen H3O+Hydronium ion

OH- Hydroxide ion

Metals MnO4- Permanganate ion

CrO42- Chromate ion

Cr2O72- Dichromate ion

Nomenclature of Polyatomic Ions Problems

• Name each of the following ions.

• OH-

• SO42-

• SO32-

• NO3-

• NH4+

Nomenclature of Polyatomic Ions Problems (Cont’d)

• Write formulas for each of the following ions.

• Hydronium ion.

• Permanganate ion.

• Perchlorate ion.

• Peroxide ion.

• Acetate ion.

Nomenclature of Polyatomic Ion Containing Compounds

• Follow the same rules as binary ionic compound nomenclature.

• Names consist of two words.• The first is the name of the positive ion, dropping the

word ion.• The second is the name of the negative ion, dropping the

word ion.• Again, the numbers of each ion is not a part of the name.• Thus, NaOH is called sodium hydroxide.• Thus, Fe(ClO)2 is called iron (II) hypochlorite or ferrous

hypochlorite.

Nomenclature of Polyatomic Ion Containing Compounds Problems

• Name each of the following compounds.

• KOH

• Li3PO4

• Na2SO4

• NH4ClO3

• NaNO3

Nomenclature of Polyatomic Ion Containing Compounds Problems

(Cont’d)• Write formulas for each of the following compounds.

• Sodium peroxide.

• Stannic borate.

• Chromium (III)Phosphate.

• Sodium carbonate.

• Lithium hydrogensulfate.

• Auric oxalate.

Nomenclature of Binary Molecular (Covalent) Compounds

• Binary covalent compounds consist of two types of nonmetal atoms.

• Greek prefixes are used to indicate the number of each type of atom.

Nomenclature of Binary Molecular (Covalent) Compounds (Cont’d)

• Greek Prefixes# Atoms Prefix

1 mono-2 di-3 tri-4 tetra-5 penta-6 hexa-7 hepta-8 octa-9 nona-10 deca-

Nomenclature of Binary Molecular (Covalent) Compounds (Cont’d)

• The order of which atom is first follows the following pattern.– The element further to the left is central.

B Si/C Sb/As/P/N H Te/Se/S I/Br/Cl O F

• The central atom is usually, but not always, listed first in its formula and name.– The central atom is usually the least

electronegative.

Nomenclature of Binary Molecular (Covalent) Compounds (Cont’d)

• Names consist of two words.• This first is prefixnonmetal.• The second prefixnonmetalide.

– The second element is given the name of its negative ion (the –ide ending).

• The mono prefix is dropped for the first nonmetal.– Any other prefix is kept.– Mono is kept for the second element.

• Thus, BBr3 is boron tribromide.• Thus B2Br6 is Diboron hexabromide.

Nomenclature of Binary Molecular (Covalent) Compound Problems

(Cont’d)• Name each of the following compounds.

• CO

• CO2

• H2O

• ClO2

• NO2

Nomenclature of Binary Molecular (Covalent)

Compound Problems (Cont’d)• Write formulas for each of the following compounds.

• Silicon dioxide.

• Nitrogen dioxide.

• Sulfur trioxide.

• Tetrasulfur tetranitride.

• Carbon tetrahydride.

Nomenclature of Acids

• For nomenclature purposes, acids are hydrogen containing compounds whose molecules yield H+ ion in water.– Note that we only use this definition for nomenclature

purposes.• To be considered an acid for nomenclature

purposes it must contain only hydrogen and negative ions.

• Not all compounds that contain hydrogen are acids.– Acids are noted by listing hydrogen as the first

element in the formula.– Of note as an exception is water, H2O.

Nomenclature of Acids (Cont’d)

• The naming for acids depends on weather or not the acid is in water.

• Acids in water are denoted by (aq) appearing next to the name.– For example, HCl(aq)

• If an acid is NOT in water, it follows the normal rules for (covalent) molecular compound nomenclature.

• If an acid is in water, it follows the naming rules for acids that follow.

Nomenclature of Acids (Cont’d)

• Acid naming follows the rules for ionic compound naming with the following differences.

• Front hydrogens are not included in the name.• The word acid is added to the end of all names.• Naming is based upon negative ion (anion)

naming which is then modified.• When writing the formulas from names, enough

hydrogens (+1 each) are added to the negative ion to produce a neutral (uncharged) molecule.

Nomenclature of Acids (Cont’d)

• Anion suffixes are replaced with acidic suffixes as follows.

• Names ending in -ate become names ending in -ic.– Thus HNO3(aq), which contain a nitrate,

becomes nitric acid.

• Names ending in -ite become names ending in -ous.– Thus HNO2(aq), which contain a nitrite,

becomes nitrous acid.

Nomenclature of Acids (Cont’d)

• Names ending in -ide become names which start with hydro- name -ending with -ic.– Thus HF, which contains a fluoride, becomes

hydrofluoric acid.

• Sulfur containing compounds are a special exception.– In these cases you add the ur in sulfur as part of the

name of the acid.– They otherwise follow the normal naming rules.

– H2S(aq) is thus hydrosulfuric acid NOT hydrosulfic acid.

Nomenclature of Acids (Cont’d)

• Phosphorous containing compounds are another special exception.– In these cases you add the or in as part of the

name of the acid.– They otherwise follow the normal naming

rules.

– H3P(aq) is thus hydrophosphoric acid NOT hydrophosphfic acid.

Nomenclature of Acids Problems

• Name each of the following acids.

• HCl(aq)

• H2SO4(aq)

• HClO(aq)

• HClO2(aq)

• HClO3(aq)

• HClO4(aq)

Nomenclature of Acids Problems (Cont’d)

• Write formulas for each of the following acids.

• Hydrocyanic acid.

• Phosphoric acid.

• Hydrobromic acid.

• Sulfurous acid.

• Oxalic acid.

• Acetic acid.

Common Names

• Some compounds also have common names.– There are literally hundreds of such names.

• These names are often brand names or the names of commonly used substances.

• In other cases, there are multiple systematic names that could be used for the same compound so a common name is used instead.

Common Names (Cont’d)

Compound Common Name Systematic NameNaCl Table salt Sodium chlorideNaHCO3 Baking soda Sodium hydrogen

carbonate (sodium bicarbonate)

MgSO4 Epsom salt Magnesium sulfateNa3PO4 Cleaning agent Sodium phosphateAl(OH)3 Antacid Aluminum hydroxideNaOH Drain cleaner Sodium hydroxideMgCO3 Plaster of Paris Magnesium

carbonateNaClO Clorox Sodium hypochloriteCaCO3 Chalk Calcium carbonate

Common Names (Cont’d)Compound Common Name Systematic Name

H2O Water Dihydrogen monoxide (hydrogen oxide, hydroxic acid)

H2O2 Hydrogen peroxide Dihydrogen dioxide(hydroperoxic acid)

NH3 Ammonia Nitrogen trihydrideN2H4 Hydrazine Dinitrogen

tetrahydrideCH4 Methane Carbon tetrahydrideC2H6 Ethane Dicarbon hexahydridePH3 Phosphine Phosphorous

trihydrideAsH3 Arsine Arsenic trihydride

Common Name Problems

• What are the systematic names and formulas for each of the following compounds?

• Water.

• Hydrogen peroxide.

• Table salt.

• Methane

• Ammonia.

Molecular and Formula Mass

• The molecular mass is the sum of all of the atomic masses of the atoms in a single molecule.

• The formula mass is the same thing except that it is the sum of all the atoms in a single formula unit.

• Most of the time the two will be exactly the same.– It is different for ionic compounds which are actually

single large molecules.• Because it is the mass for one molecule, a

molecular or formula mass is normally given in units of amu.

Determination of Formula Mass Problems

• Determine the formula mass, in amu, of each of the following compounds:– NaCl

– NH3

– CaF2

Significant Figures and Calculations Using Atomic Mass

• The number of atoms in a formula is considered exact.– So H2O contains exactly 2 hydrogens and 1

oxygen.

• Determination of formula mass is always treated as an addition problem for significant figures purposes.