Chemistry

Chapter 1.4

Compounds

 What is a compound?

 Pure substance composed of atoms of two or more different elements  What are the two types of compounds?

 Covalent and ionic compounds

Covalent Compounds

 The smallest particle of a covalent compound that has the properties of the compound is a ___________.

 Molecule  Examples:  Water, sugar, and oxygen

Ionic Compounds

 An _______ is an atom or group of atoms with an __________ _________.

 Ion,  Electrical charge  Example:  Table Salt Na + and Cl -

Compounds

 Compounds are:  Pure substances  Have a unique set of chemical properties  Have a unique set of physical properties

Compounds

 Acetic Acid  The term acid indicates that it belongs to a group of compounds with similar chemical properties  Acids all have a pH of less than 7  Can be strong or weak

Compounds

 pH:  The degree to which an aqueous solution of compound shows the properties of an acid  In water, acids have a pH of less than 7  Aspirin when dissolved in water has a pH of 2.7

Compounds

 Base:  A compound that when dissolved in water has a pH greater than 7  Some of the properties of bases are opposite of the properties of acids

Compounds

 If we don’t know the pH of an aqueous solution how do you think we would figure it out?

 Use a pH meter  Indicators  The color of the indicator will change to indicate if it is an acid or a base

Water solutions of acids…. Water solutions of bases … Taste sour Turn blue pH paper red Taste bitter and feel slippery Turn red pH paper blue Have pH values less than 7 Have pH values greater than 7 React with bases and certain metals to form salts React with acids to form salts

Organic or Inorganic

 What is the difference between an organic compound and an inorganic compound?

 Compounds that contain carbon are organic compounds.

 There are a few exceptions  Compounds that do not contain carbon are inorganic compounds

Formulas

 There are 4 different ways to represent compounds 1.

 Molecular formula: C 9 H 8 O 4  Shows the number of atoms of each element present in a molecule  Does not show how they are bonded though

Formulas

2. Structural Formula  Shows the exact number of atoms present in a molecule  Shows how the atoms are bonded together  The lines represent the bonds between atoms

Structural Formula

Formulas

3. Ball-and-stick model  Show the geometric arrangement of atoms in a formula Acetic Acid

Formulas

4. Space-fill model  Shows the geometric arrangement  Most closely represents the actual shape of the molecule

Formulas

 Look at Figure 1-21 in your text (page 28)  What do all three structural formulas have in common?

 What is unique about acetaminophen?

Mixtures

 What is a mixture?

 Collection of two or more pure substances physically mixed together  The proportions of different substances in a mixture can vary  Ex: Chicken soup

Mixtures

 The properties of a mixture can vary:  Pure gold is 24-karat gold because it is too soft to keep its shape in jewelry it is mixed with other metals to give it more strength  Gold alloy is used to make 18-karat gold  It is 18 parts gold out of 24 parts total  For even greater hardness they also make a 14-karat gold

Mixtures

 Homogeneous mixture:  All the components are uniformly distributed at the microscopic level  Gasoline, syrup, air, and 18-karat gold are all homogeneous  All regions of the mixture are identical in their composition and properties

Mixtures

 Homogeneous mixture:  The most common type of homogeneous mixture is a ____________.

 Solution  Example: Vinegar, tea, and salt water

Mixtures

 Heterogeneous mixture:  Contains substances that are not evenly distributed.

 Some regions have different properties in the mixture than others.

Heterogeneous

Orange juice or tomato juice

: Uneven distribution of components. Settles out upon standing.

Chocolate chip pecan cookie:

Uneven distribution of components Homogeneous

Iced tea

: Uniform distribution of components. Components can not be filtered out. Will not settle out

Stainless steel

: Even distribution of components

Granite:

Uneven distribution of components

Carbonated beverage:

Uniform distribution of components

Salad:

Can be easily separated by physical means

Maple syrup:

Components cannot be filtered out and will not settle upon standing

Mixtures vs. Compounds

 2 principal differences: 1.

The properties of the mixture reflect the properties of the substances it contains, but the properties of a compound often bear no resemblance to the properties of the elements that compose it.

Mixtures vs. Compounds

 2 Principal differences 2.

Compounds have definite composition by mass of their combining elements, while the components of mixtures may be present in varying proportions.

Mixtures

 How would you go about separating chemical mixtures?

 React the mixture to form a substance that can easily be removed by filtration

When is a Substance Pure?

 Is water that you drink from the tap pure? How about bottled water?

 The answer is most likely no for both because they have minerals which are considered impurities.  Are chemicals in the stockroom pure?

 They most likely also contain impurities  Standards for chemical purity have been established to control for impurities

When is a substance pure?

 Figure 1-23  Primary-standard chemicals are of a higher purity than reagent-grade  Commercial or technical grade chemicals are less expensive and because we don’t need high-purity chemicals for our experiments

Figure 1-24

 Go through the figure together!

Review Questions

 Questions 1-5  Questions 8-9  Page 32