5.2 Molecular Substances

1. 5.2 Molecular Substances

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

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

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

5. Properties • 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.

6. Molecular Elements • 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. • Molecular elements- atoms of the same element bonded together. • Why? For stability.

7. Diatomic Elements • Seven nonmetal elements are found naturally as molecular elements of two identical atoms. • Diatomic • Hydrogen – H2 - Gas • Nitrogen – N2 - Gas • Oxygen – O2 - Gas • Fluorine – F2 - Gas • Chlorine – Cl2 - Gas • Bromine – Br2 - Liquid • Iodine – I2 - Solid

8. Electron Configuration of Diatomic Elements • Oxygen • Chlorine • Nitrogen

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

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

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

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

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

14. Carbon Blacks • Make up most of the soot that collects in chimneys • 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. • Lack organization • Used in the production of printing inks and rubber products.

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

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

17. Fullerenes • Unusually stable • Group of highly organized allotropes with even-numbered molecular formulas • The buckminsterfullerene, C60 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. • After crashing into steel plates at a speed of 7000 m/s the rebound with their original shape intact. • Potential use as superconductors

18. Linear Acetylenic Carbon • Threadlike allotrope organized into long spirals of bonded carbons • Each spiral contains 300-500 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. • Used in microelectronics • Some linear acetylenic carbons may eventually form fullerenes, whereas other form soot.

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

20. Naming • Write out the name of the first nonmetal • 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. • 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

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

22. Let’s Try It! • Name the following molecular compounds • NO • NO2 • N2O • N2O5

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

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

25. Table 5. 7 Names of Common Acids and Bases

26. Naming Organic Compounds • 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. • Occur naturally in fossil fuels • Used mainly as fuels and the raw materials for making other organic compounds • Carbon can form four covalent bonds.

27. Table 5.8 Hydrocarbons

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

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

30. Homework • Read p. 176-178 and answer questions 1-3 • P. 181 #7 & 8 • P. 183 #1-3