C: Compounds

• Compounds. Huh?• A compound is an electrically neutral

substance that consists of two or more different elements with their atoms present in a definite ratio

• Compounds: Terminology– Binary: Consists of only 2 elements– Organic: Contains Carbon and hydrogen– Inorganic: No Carbon

Compounds

• The atoms are bonded together due to a chemical change– The resulting compound has physical and

chemical properties different than either of the reactants

– Eg: Hydrogen + Oxygen = Water

• Molecules: Electrically neutral compounds formed by atoms bonded together

• Ions: Positive or negatively charged atom or molecule

Ions

• Cations: Positively charged ions

• Anions: Negatively charged ions

Examples

Ionic and Molecular Compounds

• Ionic Compound: Ions form compound that is electrically neutral– Usually formed by the reaction of a metal and a nonmetal

Na(s) + Cl(g) NaCl(s)

• Molecular Compound: Binary molecular compounds are usually formed by the reaction of 2 nonmetals

2H2(g) + O2(g) 2H2O (l)

Formulas

• Chemical (or Molecular) Formula:– The composition of a compound with

chemical symbols

eg: Water, Glucose

– Composition only! Doesn’t give you an idea of how they are linked

Formulas

• Structural Formula:– Two dimensional representation of how

atoms in a molecule are linked together

eg: Ethanol

Formulas

• Line Formula: – Organic chemists sometimes omit the

carbon-hydrogen bonds knowing that carbon ALWAYS forms 4 bonds

eg: Ethanol

Other Representations

• Spacefilling model: – All atoms are spheres

and the spheres are stuck together

• Ball and Stick: – Atoms are balls and

bonds are sticks

Other Representations

• Density Isosurface: – The most probable location of

the electrons across entire molecule is shown

• Electrostatic Potential Surface: – Show the distribution of

electric charge across the density isosurface

Blue----------------------------->RedPositive Negative

Ionic Compounds• An ion forms when a compound gains or loses electrons

– The tendency to do this will be explained in the next chapter

• Ionic compounds form by the association of these positive and negative ions

How do Monatomic Ions form?

• In order to predict what type of ion an element will form, we need to look at the s and p blocks

s block Element Ionization

• Elements in the s block will lose one or two electrons depending on their group– Group 1 elements

form monovalent cations

– Group 2 elements form divalent cations

p block Element Ionization

• Elements in the p block will gain 1 to 3 electrons depending on their group– Take the group

number of the element and subtract 18 from it

Rule: Atoms gain or lose electrons until they have the same number as the nearest noble gas element

Polyatomic Ions

• Ions consisting of two or more atoms bonded together

eg: Cyanide

Ammonium

Carbonate

Nitrate

Sulfate

Common Ions You MUST know

Ionic Compounds•In ionic compounds, the ions aren’t bonded together like they are in molecular compounds

•They are associated by electric charge interactions

•The chemical formulae of ionic compounds are referring to the Ratios of anions to cations

•eg: NaCl : 1 Na+ for every Cl-

•eg: Na2CO3: 2 Na+ for every CO32-

•We need to remember the polyatomic ions to help us identify which compounds are molecular and which are ionic

How do we write the formula of an ionic compound?

•Step 1: Find the charge of the anion and the charge of the cation

•Step 2: Combine the ions in a ratio that negates the charges

•Example: Sodium chloride

•Example: Aluminum Oxide

D: The Nomenclature of Compounds

Common Name: Historic name that gives no identity of the composition

eg: Water, bleach

Systematic Name: Scientific name that reveals the composition of the compound (and sometimes its structure)

eg: Dihydrogen oxide, sodium hypochlorite

CationsCommon Name: For atoms with more than one oxidation state (transition metals)

Add -ous to the lower charge state name

Add -ic to the higher charge state name

Cu+1: Cuprous ion Fe+2: Ferrous ion

Cu+2: Cupric ion Fe+3: Ferric ion

Scientific Name: Use the element name followed by Roman numerals matching the charge state

(What are the scientific names of the ions above?)

Anions

Monatomic ions are named by adding the suffix ‘-ide’ to the stem of the element’s name (see Fluoride, chloride, oxide, bromide, sulfide above).

AnionsOxoanions can exist as multiple species, and as such,

require memorization

1. One species of oxoanion: Add the suffix ‘-ate’ to the stem of the name

Carbonate, CO32-

2. Two species of oxoanion: Add the suffix ‘-ite’ to the stem of the species with the lower number of oxygens AND add the suffix ‘-ate’ to the stem of the species with the higher number of oxygen atoms.

Nitrite, NO2- Nitrate, NO3

-

Sulfite, SO32- Sulfate, SO4

2-

AnionsOxoanions can exist as multiple species, and as such,

require memorization

1. Four species of oxoanion:

Add ‘hypo-’ to the ‘ite’ for of the name for the species with the lowest number of oxygen atoms

Add ‘per-’ to the ‘-ate’ form of the name for the species with the highest number of oxygen atoms

Hypochlorite, ClO- Chlorite, ClO2-

Chlorate, ClO3- Perchlorate, ClO4

-

Anions

Oxoanions can exist as multiple species, and as such, require memorization

1. Anions with hydrogen:

Add hydrogen to the monatomic anion name

HS-, Hydrogen sulfide

HCO3-, hydrogen carbonate

H2PO4-, Dihydrogen phosphate

Naming Ionic CompoundsIonic compounds are named by starting with the name of the

cation (and oxidation number if more than one is possible), followed by the name of the anion

• Hydrates are named by adding the word ‘hydrate’ preceded by the Greek prefix indicating the number of water molecules in the formula unit

• Step 1: Identify the cation and the anion

• Step 2: Identify the charge of the cation by looking at the anion

• Step 3: Name the cation (include the oxidation number learned in step 2)

• Step 4: Add the anion name

Naming Ionic CompoundsExamples:

NaCl

CoCl3

MgCl2•6H2O

Fe2(SO4)3

Naming Inorganic Compounds (NOT Hydrocarbons!!!)

Name the element on the left and then add the number and name of the element on the right adding the suffix ‘ide’ to the stem of the element name

PCl3 = Phosphorous trichloride

SF6 = Sulfur hexafluoride

N2O = Dinitrogen oxide

N2O5 = Dinitrogen pentoxide

Naming Inorganic Compounds (NOT Hydrocarbons!!!)

Exceptions!!!

1. Phosphorous compounds because it can have multiple oxidation states

2. Common compounds:

NH3 = Ammonia

N2O = Nitrous oxide

N2H4 = Hydrazide

H2O = Water

Summary of Naming Inorganic Compounds

Example: Write the formula of chromium (III) nitrate hexahydrate

Example: Write the formula of dinitrogen tetraoxide

Example: What is the systematic name of HNO2

Names of Common Organic Compounds

The names of organic compounds are based upon the names of the parent compounds above

•Alcohols contain -OH groups

•Carboxylic acids contain -COOH groups

•Haloalkanes contane halogens