Chapter 8Classifying Chemical Compounds

Key Ideas

• All chemical compounds are either organic

or inorganic.

• Inorganic compounds can be molecular or

ionic (acids, bases, or salts).

• Lewis diagrams (electron dot) can explain

how molecular compounds form as a

result of bonding pairs of electrons.

Key Ideas

• Organic compounds are molecular and

contain carbon and hydrogen

• All chemical compounds can be classified

as either organic or inorganic.

Classifying Inorganic Compounds

• Chemical compounds can be classified as

either organic or inorganic.

• Compounds that have a high percentage

of carbon by mass are classified as

organic compounds; otherwise they are

considered to be inorganic. (Usually have

hydrogen as well)

Inorganic compounds

• Inorganic compounds do not have a high

percentage of carbon by mass and can be

either ionic or molecular.

Inorganic Molecules

Compounds in this class are

• Inorganic, so they contain little or no carbon (most fit into this category)

• Molecular, so they have a non-metal bonded to a non-metal. (eg. CO2 ,H2O, N2O)

Inorganic Ionic Compounds

• By the 1500’s scientists had recognized

two groups of substances which became

known as acids and bases.

• When acids react with bases they create a

new substance which tasted salty. When

water was evaporated from this solution, a

crystalline substance remained

Inorganic Ionic Compounds

• Svante Arrhenius developed definitions of

acids and bases based on the type of

ions a substance releases in an aqueous

solution. Bases release OH ions (OH-1)

and acids release H ions (H+1).

General Properties of Acids, Bases, and Salts.

Acidity A solution can be acidic, basic, or neutral based

on the relative number of H or OH ions it contains.

– A neutral solution has equal numbers of H and OH ions.

– An acidic solution has more H ions than OH ions.

– A basic (alkaline) solution has more OH ions than H ions

A few water molecules form H+ and Oh- ions (about 1 in a million). In other words water is very slightly ionic.

A few water molecules form H+ and Oh- ions (about 1 in a million). In other words water is very slightly ionic.

Measuring Acidity (The pH Scale)

• The pH of a solution indicates how acidic or

basic the solution is.

• The normal range of pH is from 0 to 14, with a

pH of 7 being neutral.

• Solutions with a pH less than 7 are acidic

• Solutions with a pH greater than 7 are basic

(alkaline)

pH Values

of some common items

pH Scale

• Every 1 point on the pH scale represents

10 times more or less H+ ions present.

– Eg. A solution with a pH of 4 has 10 times

more H+ ions (10 times more acidic) than one

with a pH of 5. See table 5 page 206.

• pH indicators are chemicals that change

colour depending on the pH of a solution.

8.2 Another Look at Bonding – Lewis Diagrams

• G. N. Lewis developed a system of arranging dots around an element’s symbol that represents the valence electrons of an atom as it prepares to bond.

F F

Lewis Diagrams and Covalent Bonds

• A Lewis diagram is a simpler version of a

Bohr diagram that has only valence electrons

illustrated.

• The single valence electrons (unpaired) pair

up with another single electron from another

atom to form a shared pair, or bonding pair,

of electrons. Lewis diagrams are also called

electron dot diagrams.

Lewis Diagrams for Atoms

• A Lewis diagram can be drawn for any

atom by following a few simple rules.

1. Determine the number of valence

electrons

a. group 1 and 2 have 1 and 2 valence

electrons.

b. group 13–18 have 3-8 valence electrons.

Lewis diagrams

2. Arrange the valence electrons as dots around the atom’s symbol, just like you would in a bohr diagram. One dot per side (up to four) and then start pairing them up

Lewis Diagrams for Molecules

• Lewis diagrams can be drawn for molecules.

These diagrams illustrate how the atoms come

together to form covalent bonds.

• To draw a Lewis diagram for a molecule, you

must first be given the molecular formula.

Atoms are then connected to one another by

pairs of shared electrons, or bonding pairs.

Example: Water

Lewis Diagrams

• The purpose of a Lewis diagram is to

illustrate that the formation of these

covalent molecules is possible.

• Lewis diagrams can also be drawn for ions

and ionic compounds, but we will not be

doing this.