Chapter 8 Classifying 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) 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. Determine the number of valence electrons group 1 and 2 have 1 and 2 valence electrons. group 13–18 have 3-8 valence electrons.

Lewis diagrams 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.