Chem 11

Exam 3 Review

November 13, 2006,

Exam Topics

• Naming compounds

• Writing formulas

• Ion names and charges

• Balancing equations

• Recognize ionic and covalent

• Use Lewis structures to get bonds and lone pairs

• Electronegativity

• Isoelectronic/Identical to

Nomenclature Terms

Binary Compound : contains 2

elements

Binary Ionic Compound : a metal and a nonmetal -> metal named first If metal has more than one

charge must indicate charge with (Roman numerals) or

Latin endings

-ous = lower charge - ic = higher charge

Nomenclature Terms

Binary Covalent Compound:two nonmetals

Least electronegative element named first

Second element has -ide ending

Greek prefixes indicate subscripts

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

Nomenclature Terms

Nonbinary Compound:more than two elements

- probably contains polyatomic ion(s)

- Name the polyatomic cation first

- Name the polyatomic anion second

- MUST KNOW the polyatomic ions by name and formula to recognize them

Nomenclature Flow Chart

Single-Charge Multiple-Charge Metal Metal

Name the metal

Indicate metal charge by (Roman #) or Latin

name (-ous or –ic)

+ 1 nonmetal

+ 2 nonmetals

Name the polyatomic ion Nonmetal name

with –ide ending

*Metal + Nonmetal

Chemical Formula

2 Nonmetals

1) Use Greek prefixes to indicate subscripts

2) second element –ide ending

H + Nonmetal(s)

Name as acids

* Treat NH4+ as a metal when

naming compounds

Naming of Acids

• If anion does not contain oxygen:– Start with Hydro-– Add –ic to the end– Ex: HCl: Cl- is chloride, so the acid is

Hydrochloric acid

• If anion contains oxygen:– Look at the ending

– If –ite, use anion root and -ous

– Ex: HNO2: NO2- is nitrite, so the acid

is Nitrous acid

– If –ate, use anion root and -ic

– Ex: H2SO4: SO42- is sulfate, so the

acid is Sulfuric acid

Nomenclature Practice

Name the following compounds: Ba(OH)2

NaC2H3O2

Fe3(PO4)2

CaS

MgSO4

K2SO3

P2O5

N2O

SO3

LiF

Monoatomic Cations

Metal atoms can lose valence electrons and become positively charged cations.

Naming Cations: The parent atom gets the word “ion”.

Na+ “sodium ion”

Al3+ “aluminum ion”

This rule applies for metals that usually form one ion.

Metals That Form Multiple Ions

If Metal Forms More than One Cation:

The parent metal gets the charge in Roman numerals in parentheses and followed by the word “ion”.

Fe2+ is the iron(II) ion, ferrous (old name)

Fe3+ is the iron(III) ion, ferric (old name)

This is called the Stock system of naming cations.

Monoatomic Anions

Nonmetals can gain valence electrons and become negatively charged anions.

Monoatomic anions are named by dropping the end of the element name and adding the suffix –ide.

Br- “bromide ion”

O2- “oxide ion”

N3- “nitride ion”

Predicting Cation Formulas

Group IA/I metals always form +1 ions and Group IIA/I ions always form +2 ions.

Group IIIA/13 metals are predicted to form 3+ ions.

Not all metal ion charges are predictable.

Tin and lead in Group IVA/14 form both +2 and +4 ions.

Most transition metals form +2 ions from the loss of their 2 s-electrons.

Metals and Their Cation Charges

Predicting Anion ChargesNonmetals gain electrons to form anions Group VIIA/17 atoms gain 1 electron to form -1 ions:

F-, Cl-, Br-, and I-

Group VIA/16 atoms gain 2 electrons to form -2 ions:

O2-, S2-, Se2-, and Te2-.

Group VA/15 atoms gain 3 electrons to form -3 ions:

N3-, P3-, and As3-.

Polyatomic AnionsOxyanions:

Polyatomic anions containing one or more elements combined with oxygen are called oxyanions.

Most oxyanions have names that end in the suffix -ate.

SO42- “sulfate ion”

NO3- “ nitrate ion”

Naming Oxyanions

Some oxyanions end in the suffix -ite.

NO2- “nitrite ion”

SO32- “sulfite ion”

The oxyanions that end in -ite each have one less oxygen than the oxyanions (compared to the oxyanions ending in –ate, sulfate SO4

2- and nitrate NO3-).

Writing Ionic Formulas

Ionic compound: Composed of positive and negative ions. Formula unit shows an ionic compound.

A formula unit is neutral, so the total positive charge must equal the total negative charge in the formula unit.

When writing chemical formulas, the cation (metal) goes first and the anion (nonmetal) goes second.

Formulas of Ionic Compounds

• If the charges of the ions are the same, formula unit contains one of each ion.

Na+ and Cl- form NaCl.

Mg2+ and S2- form MgS.

• If the charges are not equal, balance the positive and negative charges.

Ca2+ and Cl- form CaCl2.

Na+ and O2- form Na2O.

Formulas with Polyatomic Ions

Follow the same rules as binary ionic compounds; if the charges are equal, the formula has one of each ion.

Mg2+ and SO42- combine to form

MgSO4

K+ and ClO3- combine to form

KClO3

If the charges are not equal, the total charge must equal zero. If you have more than one polyatomic ion, it is placed in parentheses.

Al3+ and CO32- combine to form

Al2(CO3)2.

Naming Binary Ionic Compounds

Combine the cation and anion name (drop “ion”) in the following order :

first cation and second anion.

Example:

MgO is composed of one magnesium ion and one oxide ion

The name is magnesium oxide.

Cont’d…Naming Binary Ionic Compounds

Question: What is the name of cinnabar, HgS?

Hg2+ is the mercury(II) ion and

S2- is the sulfide ion,

The name is mercury(II) sulfide.

Naming Ternary Ionic Compounds

Name ternary ionic compounds like binary ionic compounds: the cation name followed by the anion name.

Example: K2CO3 is named potassium carbonate.

If metal can have more than one oxidation state, determine the charge on the metal.

Example: Co(ClO3)3 is composed of cobalt(III) and chlorate ions.

cobalt(III) chlorate

Binary Molecular Compounds

They are composed of two nonmetal elements. A molecule is the simplest representation of a binary molecular compound.

IUPAC has set the following order, according to increasing electronegativity, for writing elements in a binary molecular compound:

– C, P, N, H, S, I, Br, Cl, O, F

Naming Binary Molecular Compounds• The first element in the compound is

named first and the second element has the suffix -ide.

• The number of atoms of each element must be indicated by Greek prefixes.

Prefix Number IndicatingMono- 1Di- 2Tri- 3Tetra- 4Penta- 5Hexa- 6Hepta- 7Octa 8

Cont’d…Names of Binary Molecular Compounds

Example:

What is the name of the molecular compound P4S3?

– 4 P atoms tetra-

– 3 S atoms tri-

– P4S3 is tetraphosphorous trisulfide.

What is the name for Br3O8?

– tribromine octaoxide.

Exceptions

Exception to the use of the Greek prefixes when naming binary molecular compounds.

If only one atom exists in the first element “mono-” is not used. The prefix mono- is always used for the second element.

– CO is carbon monoxide

– IF6 is iodine hexafluoride

Binary Acids

A binary acid is an aqueous solution of a compound containing hydrogen and a nonmetal.

The formula of an acid always begins with H:

– HF (aq)

Binary acids are named using the prefix hydro- before the element and adding the suffix “-ic acid”.

– HF (aq) is hydrofluoric acid

– H2S (aq) is hydrosulfuric acid

Ternary Oxyacids

Ternary oxyacids are aqueous solution of a compound containing hydrogen and an oxyanion.

If acid is derived from an oxyanion ending in -ate, suffix is changed to “-ic acid”.

HNO3 (aq) is nitric acid (from NO3-,

nitrate ion)

If acid is derived from an oxyanion ending in -ite, suffix is changed to “-ous acid”.

HNO2 (aq) is nitrous acid (from NO2-,

nitrite ion)

Lewis Structure for SO3

1. Count the total number of valence electrons: each oxygen has 6 and sulfur has 6 for a total of 24 electrons [3(6) + 6 = 24 e-]. This gives us 12 electron pairs.

2. Place 4 electron pairs around the central sulfur atom and attach the three oxygens. We started with 12 electron pairs and have 8 left.

3. Place the remaining electron pairs around the oxygen atoms to complete each octet.

4. One of the oxygens does not have an octet, so move a nonbonding pair from the sulfur to provide 2 pairs between the sulfur and the oxygen.

Cont’d…Lewis Structure for SO3

Electronegativity• Electronegativity increases from

left to right in a period.

• Electronegativity increases from bottom to top in a group.