chapter 8 classifying chemical compounds. key ideas all chemical compounds are either organic or...
TRANSCRIPT
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.