Molecules and Molecules and CompoundsCompounds

(Nomenclature)(Nomenclature) Chapter 5Chapter 5

Tro, 2Tro, 2ndnd ed. ed.

Molecules and Compounds

Pair up and look up this law and then write it in your own words to share with the rest of the class. Give examples other than what is in the textbook.

Law of Constant Composition

HOW TO LEARN NOMENCLATURE

Memorize, memorize, memorize!

Memorize the rules for naming

Memorize names of ions

Memorize some acid names and some organic names

Types of Compounds and Naming Types of Compounds and Naming RulesRulesCompound

Ionic (formula unit) Covalent (molecule)

Salts Hydrates Other Binary (Ternary) Organic Acids Other

Binary

Polyatomic Ions

You will learn all the rules for ionic, hydrates, covalent binary, and only specific common names, organic compounds and acids.

Common and Systematic Names

Chemical nomenclature is the system of names that chemists use to identify compounds. Two classes of names exist: common names and systematic names.

Common names are arbitrary names.They are not based on the composition of the compound.They are based on an outstanding chemical or physical

property.Common names that you need to memorize: acetylene,

ammonia, water, baking soda, cane sugar, epsom salts, grain alcohol, laughing gas, lye, muriatic acid, table salt, vinegar, washing soda, and wood alcohol. (common name, formula and systematic name)

Ammonia, NH3

Chemists prefer systematic names.

Systematic names precisely identify the chemical composition of the compound.

The present system of inorganic chemical nomenclature was devised by the International Union of Pure and Applied Chemistry (IUPAC).

The formula for most elements is the symbol of the element.

Sodium NaPotassium K

Zinc ZnArgon Ar

Mercury HgLead Pb

Calcium Ca

Hydrogen H2

Nitrogen N2

Oxygen O2

Fluorine F2

Chlorine Cl2Bromine Br2

Iodine I2

These 7 elements are found in nature as diatomic molecules.

→remove e-

neutral atom

A charged particle known as an ion can be produced by adding or removing one or more electrons from a neutral atom.

cation

If one or more electrons are removed from a neutral atom a positive ion is formed. A positive ion is called a cation.

MONATOMIC IONS:

Metals always lose electrons to form positive ions, called cations

If element forms only one cation, we name it by its element name: Na+ = sodium ion Al3+ = aluminum ion

If a transition metal can form more than one cation, add ion’s charge in Roman numerals to the name. Fe2+ is iron(II) ion and Fe3+ is iron(III) ion. (Old names, ferrous and ferric.)

→neutral atom

A charged particle known as an ion can be produced by adding or removing one or more electrons from a neutral atom.

If one or more electrons are added to a neutral atom a negative ion is formed. A negative ion is called an anion.

add e-

anion

MONATOMIC IONS:

Nonmetal atoms gain electrons to form negative ions, called anions

Take the root of the element name and add “-ide”Cl- = chloride ion Se2- = selenide ionN3- = nitride ion

Most often ions are formed when metals combine with nonmetals. (Exception is NH4

+ with anion.)

The charge on an ion can be predicted from its position in the periodic table.

elements of Group IIA have a

+2 charge

elements of Group IA have a +1 charge

elements of Group VA have a

-3 charge

elements of Group VIA have a

-2 charge

elements of Group VIIA have a

-1 charge

NAMING IONIC COMPOUNDS:

Always put cation before anion in formula. Name of compound is just cation name followed by anion name.MgF2 is Mg2+ and F- = magnesium fluorideFeBr3 is Fe3+ and Br- = iron(III) bromide

What is the formula for silver carbonate? Silver ion is Ag+ and carbonate CO3

2- - have to balance charges, so need 2 Ag+ for each CO3

2- = Ag2CO3

Generic: Ma+bNb-

a criss-cross rule However, if a = b, then both = 1 by definition for lowest ratio

Figure out the charge on each x: ZnX, NH4X, (NH4)2X, Al2X3, X2(SO3)3

Write the formula of barium phosphide.

Step 1. Write down the formulas of the ions.Ba2+ P3-

Step 2. Combine the smallest numbers of Ba2+ and P3- so that the sum of the charges equals zero.

3(2+) + 2(3-) = 0The correct formula is Ba3P2

The lowest common multiple of +2 and –3 is 6

3(Ba2+) + 2(P3-) = 0

The cation is written first.

The anion is written second.

Naming Compounds Containing Polyatomic Ions

A polyatomic ion is an ion that contains two or more elements.

Compounds containing polyatomic ions are composed of three or more elements.

They usually consist of one or more cations combined with a negative polyatomic ion.

When naming a compound containing a polyatomic ion, name the cation first and then name the anion.

-3NO

2 3Na CO

This is the way theformula is written.

2 3Na CO

The ions are what isactually present.

+2Na 2-3CO

Elements that Form More than One Polyatomic Ion with

OxygenAnions ending in -ate always contain

more oxygen than ions ending in -ite. nitrite

-2NO

nitrate-3NO

phosphite3-3PO

phosphate3-4PO

One group of ionic compounds that contains all nonmetals is the ammonium salts. Try to write formulas for ammonium sulfate and ammonium phosphate.

ANIONS WITH HYDROGEN

Some anions have picked up one or two hydrogen ions. Old naming rules put “bi” in front of the anion name. IUPAC uses hydrogen or dihydrogen:

CO32- with one H+ added is HCO3

-

Carbonate ion becomes hydrogen carbonate ion.

Name these: PO43-, HPO4

2-, H2PO4-

Four polyatomic ions that do not use the –ate/ite system.

hydroxide-OH

hydrogen sulfide-HS

cyanide-CN

peroxide2-2O

There are three common positively There are three common positively charged polyatomic ions.charged polyatomic ions.

ammonium+4NH

hydronium+

3H O

mercury(I)2+2Hg

Divide the formula into cation(s) and anion. Name each.

For example KHSO4 is K+ and HSO4-.

MgNH4PO4 is Mg2+, NH4+ and PO4

3-.

(So you can see relationship between anions and acids.)

Binary CompoundsBinary compounds contain only two different elements. There are four

main types, listed in following slides.

A. Binary Ionic Compounds Containing a Metal Forming Only One Type of Cation (salts)

Binary ionic compounds consist of a metal combined with a non-metal.The chemical name is composed of the name of the metal followed by

the name of the nonmetal which has been modified to an identifying stem plus the suffix –ide.

Using this system the number of atoms of each element present is not expressed in the name.

Practice: CaC2, MgBr2, Al2O3, NaH(calcium carbide, magnesium bromide, aluminum oxide, sodium

hydride)

Binary CompoundsB. Binary Ionic Compounds Containing a Metal

That Can Form Two or More Types of Cations (still salts)The chemical name is composed of the name of the metal with its

charge in Roman numerals, followed by the name of the nonmetal which has been modified to an identifying stem plus the suffix –ide.

Using this system the number of atoms of each element present is not expressed in the name.

Practice: FeS, CuCl2, SnF2, Mn3(PO4)5

(iron (II) sulfide, tin(II) fluoride, manganese (V) phosphate)

Lower Charge Higher Charge Element Formula Name Formula Name

Copper Cu+ cuprous Cu2+ Cupric

Iron Fe2+ ferrous Fe3+ ferric

Lead Pb2+ plumbous Pb4+ plumbic

Mercury Hg mercurous Hg2+ mercuric

Tin Sn2+ stannous Sn4+ stannic

Ion Names: Classical System

2+2

This is for information and for homework only; classical names will not be on quiz or test unless part of a common name that’s required.

Binary CompoundsC. Binary Compounds Containing Two Nonmetals (Binary

Covalent) Compounds between nonmetals are molecular, not ionic.

In a compound formed between two nonmetals, the element that more electropositive (least electronegative) is named first.

Rules for naming: 1. Give Greek prefix (to indicate number of atoms of first element) to name of first element. Don’t use mono prefix for first element.2. Give Greek prefix (to indicate number of atoms of second element) to root of element name, then add -ide

Example: N2O3 is dinitrogen trioxide.Exception: hydrogen never has prefix.

Greek Prefixes

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

Binary CompoundsC. Binary Compounds Containing Two Nonmetals (Binary Covalent) ExamplesN2O3, PCl5, Cl2O7, CCl4, CO, CO2, PI3, H2S

Dinitrogen trioxidePhosphorous pentachloride (not mono-)Dichlorine heptoxideCarbon tetrachlorideCarbon monoxideCarbon dioxidePhosphorous triiodideHydrogen sulfide (hydrogen never gets a prefix)

Now try: CS2, H2O, N2O4, SF2, SiCl2, P2O5, phosphorous trichloride, dichlorine oxide

Binary CompoundsD. Acids Derived from Binary Compounds Certain binary hydrogen compounds, when

dissolved in water, form solutions that have acid properties.

The aqueous solutions of these compounds are given acid names.

The acids names are in addition to their –ide names.

Hydrogen is typically the first element of a binary acid formula.

Acid Formation

waterAcid sol.

binary hydrogen compound like HCl is called hydrogen chloride (not an acid yet).

Now it’s hydrochloric acid.

Binary CompoundsD. Acids Derived from Binary Compounds To name binary acids write the symbol of

hydrogen first. After hydrogen write the symbol of the second element.

Place the prefix hydro- in front of the stem of the nonmetal name. Place the suffix -ic after the stem of the nonmetal name.

Practice: HCl, H2S, HI(hydrochloric acid, hydrosulfuric acid, hydroiodic

acid)

A.

B.

C.

D.

The other element is usually a nonmetal, but it can be a metal.

The first element listed in the formula is hydrogen.

The remainingelements include oxygen and form a polyatomic ion.

The word acid in the name indicates the presence of hydrogen.

Oxy-acids contain hydrogen, oxygen and one other element.Hydrogen in an oxy-acid is not expressed in the acid name.

More Acids

contains oxygen

contains sulfur

contains hydrogen

indicates hydrogen

sulfuric acid 42SOH

This is one of the six acids you have to know.

(If you add HCl to the ones marked by arrows, you have your total list of acids.)

Your AcidsAn acid is a substance that forms H+ when

dissolved in water Some are strong acids, that means all the H+

dissolves and dissociates from the anionSome acids are weak, meaning very little H+

dissociates, although the cmpd dissolvesForget sections in text: just learn these!

Hydrochloric acid, sulfuric acid, and nitric acid are strong acids: HCl(aq), H2SO4(aq), HNO3(aq)

Acetic acid, carbonic acid, phosphoric acid are weak acids: HC2H3O2(aq), H2CO3(aq), H3PO4(aq)

Your Organic Compounds

No naming rules – just learn formulas and names.

CH4 methane, C3H8 propane, C8H18 octane, CH3OH methanol, CH3CH2OH ethanol, C6H6 benzene, CH3COOH acetic acid (organic method), CH3NH2 aminomethane, C6H12O6 glucose, C12H22O11 sucrose, and C2H2, ethyne

HYDRATES: (not in book) Also a good review of ionic names!If an ionic compound is a hydrate, it will

have *H2O in the formula, like MgCO3*6 H2O

Name the ionic compound part using ionic naming rules, then give the Greek prefix for the number of water molecules and add the word hydrate: MgCO3*6H2O is magnesium carbonate hexahydrate

HYDRATES: (not in book) Also a good review of ionic names!

Examples: you name the following (notice their common names)gypsum CaSO4*2 H2Oepsom salts MgSO4*7 H2Owashing soda Na2CO3*10 H2Obluestone CuSO4*5 H2O

Calcium sulfate dihydrateMagnesium sulfate heptahydrateSodium carbonate decahydrateCopper(II) sulfate pentahydrate

Formula Mass

As each element’s atom has mass in amu on the Periodic Table, so do molecules and formula units.

Formula mass is the sum of the atomic masses of the atoms in the chemical formula.

Practice: water, sodium chloride, acetic acid