5.2 Molecular Substances

Objectives Compare the properties of molecular and ionic substances. Compare the properties of molecular and ionic substances. Distinguish among allotropes of an element. Distinguish among allotropes of an element. Apply formulas to name molecular compounds. Apply formulas to name molecular compounds.

Properties of Molecular Substance Molecular substance- a substance that has atoms held together by covalent bonds Molecular substance- a substance that has atoms held together by covalent bonds Properties are more variable Properties are more variable Polyethylene plastic = soft Polyethylene plastic = soft Quartz = hard Quartz = hard

Properties Low melting and boiling points Low melting and boiling points Less soluble in water Less soluble in water Not electrolytes Not electrolytes Interparticles forces between molecules are weak and easily broken. Interparticles forces between molecules are weak and easily broken. Explains the softness and low melting points of most molecular substances Explains the softness and low melting points of most molecular substances

Properties Different enough that the differences can be used to classify and separated them from one another. Different enough that the differences can be used to classify and separated them from one another. Distillation- method of separating substances in a mixture by evaporation of liquid and subsequence condensation of its vapor. Distillation- method of separating substances in a mixture by evaporation of liquid and subsequence condensation of its vapor.

Molecular Elements Molecules vary greatly in size Molecules vary greatly in size Most elements occur in nature bonded to another element, but some occurs as atoms of the same element bonded together. Most elements occur in nature bonded to another element, but some occurs as atoms of the same element bonded together. Molecular elements- atoms of the same element bonded together. Molecular elements- atoms of the same element bonded together. Why? For stability. Why? For stability.

Diatomic Elements Seven nonmetal elements are found naturally as molecular elements of two identical atoms. Seven nonmetal elements are found naturally as molecular elements of two identical atoms. Diatomic Diatomic Hydrogen – H 2 - Gas Hydrogen – H 2 - Gas Nitrogen – N 2 - Gas Nitrogen – N 2 - Gas Oxygen – O 2 - Gas Oxygen – O 2 - Gas Fluorine – F 2 - Gas Fluorine – F 2 - Gas Chlorine – Cl 2 - Gas Chlorine – Cl 2 - Gas Bromine – Br 2 - Liquid Bromine – Br 2 - Liquid Iodine – I 2 - Solid Iodine – I 2 - Solid

Electron Configuration of Diatomic Elements Oxygen Oxygen Chlorine Chlorine Nitrogen Nitrogen

Allotropes Allotropes-molecules of a single element that differ in crystalline or molecular structure. Allotropes-molecules of a single element that differ in crystalline or molecular structure. Oxygen and Ozone Oxygen and Ozone Ozone is the most common form in atomsphere Ozone is the most common form in atomsphere Structural differences Structural differences

Ozone Occurs naturally and is formed from diatomic oxygen by lightning or ultraviolet light. Occurs naturally and is formed from diatomic oxygen by lightning or ultraviolet light. Sharp odor Sharp odor Also formed from TV sets or computer monitors Also formed from TV sets or computer monitors Ozone is harmful to living things Ozone is harmful to living things Uses Uses Small amounts of ozone is used to purify water Small amounts of ozone is used to purify water Treat clothing, carpeting and other material damaged by smoke Treat clothing, carpeting and other material damaged by smoke Used to remove cigarette smell Used to remove cigarette smell Layer high in our atmosphere helps to shield organisms from harmful UV radiation Layer high in our atmosphere helps to shield organisms from harmful UV radiation

Phosphorus Allotropes Three allotropes Three allotropes White-will ignite spontaneously in air and must be stored under water White-will ignite spontaneously in air and must be stored under water Red-used in the strike pad of safety matches Red-used in the strike pad of safety matches Black- is a semiconductor Black- is a semiconductor Each has unique structure and properties Each has unique structure and properties Figure 5.15 p. 179 Figure 5.15 p. 179

Carbon Allotropes Several important ones Several important ones Graphite Graphite Carbon Blacks Carbon Blacks Diamond Diamond Charcoals Charcoals Fullerenes Fullerenes Linear Acetylenic Carbon Linear Acetylenic Carbon

Graphite Most common form of carbon Most common form of carbon Atoms are linked to each other in a continuous sheet of hexagons Atoms are linked to each other in a continuous sheet of hexagons Well organized structure Well organized structure The looseness between layers is why graphite is useful to write with. The looseness between layers is why graphite is useful to write with.

Carbon Blacks Make up most of the soot that collects in chimneys Make up most of the soot that collects in chimneys Formed by the incomplete burning of hydrocarbon compounds. Formed by the incomplete burning of hydrocarbon compounds. Each microscopic chunk of carbon is make up of millions of jumbled chunks of layered carbon atoms. Each microscopic chunk of carbon is make up of millions of jumbled chunks of layered carbon atoms. Lack organization Lack organization Used in the production of printing inks and rubber products. Used in the production of printing inks and rubber products.

Diamond Hardest natural substance Hardest natural substance Often used on the tips of cutting tools and drills. Often used on the tips of cutting tools and drills. Structure: every carbon atom is attached to four other carbon atoms Structure: every carbon atom is attached to four other carbon atoms One of the most organized of all substances One of the most organized of all substances This organization of covalent bonds accounts for the hardness of diamonds. This organization of covalent bonds accounts for the hardness of diamonds. Formed under extreme pressure and temperature. Formed under extreme pressure and temperature. Diamonds range in age from 600 million to 3 billion years old Diamonds range in age from 600 million to 3 billion years old

Charcoals Poorly organized carbon molecules. Poorly organized carbon molecules. Produced from the burning of organic matter Produced from the burning of organic matter Charcoal is extremely porous  great surface area Charcoal is extremely porous  great surface area Useful for removing odors and tastes(activated charcoal) Useful for removing odors and tastes(activated charcoal)

Fullerenes Unusually stable Unusually stable Group of highly organized allotropes with even- numbered molecular formulas Group of highly organized allotropes with even- numbered molecular formulas The buckminsterfullerene, C 60 discovered in 1985 in soot and the shape confirmed in 1991 (p. 178) The buckminsterfullerene, C 60 discovered in 1985 in soot and the shape confirmed in 1991 (p. 178) Some molecules are hollow spheres other are hollow tubes with great flexibility. Some molecules are hollow spheres other are hollow tubes with great flexibility. After crashing into steel plates at a speed of 7000 m/s the rebound with their original shape intact. After crashing into steel plates at a speed of 7000 m/s the rebound with their original shape intact. Potential use as superconductors Potential use as superconductors

Linear Acetylenic Carbon Threadlike allotrope organized into long spirals of bonded carbons Threadlike allotrope organized into long spirals of bonded carbons Each spiral contains carbon atoms. Each spiral contains carbon atoms. Produced by using a laser to zap a graphite rod into a glass container filled with argon gas. The allotrope splatters on the glass and is then removed. Produced by using a laser to zap a graphite rod into a glass container filled with argon gas. The allotrope splatters on the glass and is then removed. Used in microelectronics Used in microelectronics Some linear acetylenic carbons may eventually form fullerenes, whereas other form soot. Some linear acetylenic carbons may eventually form fullerenes, whereas other form soot.

Naming Binary Inorganic Compounds Organic compounds- compounds that contain carbon Organic compounds- compounds that contain carbon Inorganic compounds- compounds that do not contain carbon Inorganic compounds- compounds that do not contain carbon Molecular Binary Compounds Molecular Binary Compounds Contain only two nonmetal elements Contain only two nonmetal elements bonded covalently bonded covalently

Naming Write out the name of the first nonmetal Write out the name of the first nonmetal Follow it by naming the second nonmetal with its ending changed to –ide Follow it by naming the second nonmetal with its ending changed to –ide You write the first the element that is farther to the left on the periodic table, with the exceptions of a few compounds that contain hydrogen. You write the first the element that is farther to the left on the periodic table, with the exceptions of a few compounds that contain hydrogen. If the elements are in the same group, name first the element that is closer to the bottom of the periodic table If the elements are in the same group, name first the element that is closer to the bottom of the periodic table A prefix is need when more than one atom is present for the first of the two and always used for the second atom of a molecule A prefix is need when more than one atom is present for the first of the two and always used for the second atom of a molecule

Prefixes When a vowel combination (o-o or a-o) appears next to each other the first of the pair is usually omitted. When a vowel combination (o-o or a-o) appears next to each other the first of the pair is usually omitted. Mono- = 1 Mono- = 1 Di- = 2 Di- = 2 Tri- = 3 Tri- = 3 Tetra- = 4 Tetra- = 4 Penta- = 5 Penta- = 5 Hexa- = 6 Hexa- = 6 Hepta- = 7 Hepta- = 7 Octa- = 8 Octa- = 8 Nona- = 9 Nona- = 9 Deca- = 10 Deca- = 10

Let’s Try It! Name the following molecular compounds Name the following molecular compounds NO NO NO 2 NO 2 N 2 O N 2 O N 2 O 5 N 2 O 5

Let’s Try It! Write the formula for the following molecular compounds. Write the formula for the following molecular compounds. Carbon disulfide Carbon disulfide Carbon monoxide Carbon monoxide Sulfur hexafluoride Sulfur hexafluoride Dinitrogen trioxide Dinitrogen trioxide

Common Names A few inorganic compounds have common names that all scientists use in place of formal names. A few inorganic compounds have common names that all scientists use in place of formal names. Examples: Examples: Water Water Ammonia Ammonia Also acids and bases Also acids and bases

Table 5. 7 Names of Common Acids and Bases FormulaName AcidsHCl H 2 SO 4 H 3 PO 4 HNO 3 HC 2 H 3 O 2 BasesNaOHKOH NH 3 Hydrochloric acid Sulfuric acid Phosphoric acid Nitric acid Acetic acid (organic compound) Sodium hydroxide Potassium hydroxide ammonia

Naming Organic Compounds The name of even the most complex organic compound is based on the name of a hydrocarbon. The name of even the most complex organic compound is based on the name of a hydrocarbon. Hydrocarbon- a organic compound that contains only the elements hydrogen and carbon. Hydrocarbon- a organic compound that contains only the elements hydrogen and carbon. Occur naturally in fossil fuels Occur naturally in fossil fuels Used mainly as fuels and the raw materials for making other organic compounds Used mainly as fuels and the raw materials for making other organic compounds Carbon can form four covalent bonds. Carbon can form four covalent bonds.

Table 5.8 Hydrocarbons FormulaName CH 4 C 2 H 6 C 3 H 8 C 4 H 10 C 5 H 12 C 6 H 14 C 7 H 16 C 8 H 18 C 9 H 20 C 10 H 22 MethaneEthanePropaneButanePentaneHexaneHeptaneOctaneNonanedecane

Connecting Ideas Formulas represent the know composition of real substances Formulas represent the know composition of real substances But just because you can write the formula does not mean it can exist. But just because you can write the formula does not mean it can exist.

Review Compare ionic and molecular compounds. Compare ionic and molecular compounds. What are the allotropes of carbon and something about each? What are the allotropes of carbon and something about each? What are the allotropes of phosphorous and something about each? What are the allotropes of phosphorous and something about each?

Homework Read p and answer questions 1-3 Read p and answer questions 1-3 P. 181 #7 & 8 P. 181 #7 & 8 P. 183 #1-3 P. 183 #1-3