Science 9 Alkanes Elements thingsss.pptx

All about alkanes

1. Lesson 11.1 Alkanes

2. describe the properties of alkanes; 1 At the end of the lesson, you should be able to: r ecognize the common examples and uses of alkanes; 2 write structural formulas for alkanes; and 3 name alkanes based on their structures. 4

3. These are a group of hydrocarbon compounds that contain carbon-carbon single (C-C) bonds and carbon-hydrogen (C-H) bonds only. It has a general formula of C n H 2n+2 where n is the number of carbon atoms (n=1, 2, 3, …). Their names end in -ane . Since alkanes are the only hydrocarbons that contain purely single bonds throughout their structures, they are classified as saturated hydrocarbons . Alkanes

4. Alkanes are insoluble in water, but are soluble in organic solvents such as toluene and chloroform. They are also less dense than water. The physical state of alkanes at room temperature varies depending on the number of carbon atoms. those with one to four carbon atoms are gases; those with five to seventeen carbon atoms are generally liquid; and those beyond seventeen carbons are solids. Properties of Alkanes

5. Alkanes generally have low melting and boiling points. As more carbon atoms are added to the alkane chain, there is an increase in melting and boiling points, increase in viscosity, and decrease in flammability. Alkanes are also known to be generally unreactive. These compounds consist only of single carbon-carbon bonds and carbon-hydrogen bonds which are strong and hard to break. Properties of Alkanes

6. Alkanes may come into two forms: straight-chain and branched-chain. Straight-chain alkanes can be seen as a continuous row of carbons. Branched-chain alkanes are composed of a parent chain and alkyl groups. Naming Alkanes

7. In the case of nomenclature, straight-chain alkanes can be easily named with the first part of its name representing the number of carbon atoms and the suffix -ane representing the hydrocarbon group, alkane . For example, methane can be analyzed with meth- defining one carbon in the compound, and -ane signaling that the compound is purely an alkane. Naming Straight-Chain Alkanes

8. Number of Carbon Atoms Name (Molecular Formula) Kekule Structures Condensed Structure 1 methane (CH 4 ) CH 4 2 ethane (C 2 H 6 ) CH 3 CH 3 3 propane (C 3 H 8 ) CH 3 CH 2 CH 3 Table 1. Some examples of straight-chain alkanes and their corresponding nomenclature, Kekule structures, and condensed structures.

9. Number of Carbon Atoms Name (Molecular Formula) Kekule Structures Condensed Structure 4 butane (C 4 H 10 ) CH 3 CH 2 CH 2 CH 3 5 pentane (C 5 H 12 ) CH 3 CH 2 CH 2 CH 2 CH 3 6 hexane (C 7 H 14 ) CH 3 CH 2 CH 2 CH 2 CH 2 CH 3 Table 1. Some examples of straight-chain alkanes and their corresponding nomenclature, Kekule structures, and condensed structures.

10. To illustrate straight-chain alkanes, we can make use of the three main structural methods: condensed , Kekule , and skeletal structure . How to write/draw a condensed structure : O nly the symbols for carbon and hydrogen (and its subscripts) are shown; hence, no line bonds. e.g., butane: CH 3 CH 2 CH 2 CH 3 The single bonds between carbons are not shown through line bonds as it is understood already that those bonds exist and need not to be emphasized. Drawing Straight-Chain Alkanes

11. How to draw the Kekule structure : It is drawn by explicitly writing the symbols of each atoms and the bonds that exists between two atoms. It is also comparable to drawing the Lewis structures of inorganic covalent compounds. Kekule structures of straight-chain alkanes are seen in Table 1. Drawing Straight-Chain Alkanes

12. How to draw the skeletal structure ( line angle formula ) : They are represented by line segments connected through a zigzag direction. Endpoints represent carbon atoms. The symbols of carbon and hydrogen are not shown for the purpose of simplification. The zigzag direction signifies the valence bond model of each carbon atom (sp 3 orbitals found in carbon atoms in alkanes results to electrons making an angle of 109.5 o , thus the zigzag direction). Drawing Straight-Chain Alkanes

13. Number of Carbon Atoms Name (Molecular Formula) Skeletal structures 3 propane (C 3 H 8 ) 4 butane (C 4 H 10 ) 5 pentane (C 5 H 12 ) 6 hexane (C 6 H 14 ) 7 heptane (C 7 H 16 ) Table 2. Some examples of straight-chain alkanes and their corresponding nomenclature and skeletal structures.

14. To name branched-chain alkanes, you may refer to the order of naming below: Naming Branched -Chain Alkanes Basic technique in naming branched-chain alkanes

15. In naming and drawing alkanes, the following terms should be considered: The parent chain is defined as the longest straight-chain alkane present in the hydrocarbon structure. Substituents are alkyl groups attached to one or more non-terminal carbon atoms belonging to parent chain. The locant represents the number of carbon where the substituents are attached. Naming Branched-Chain Alkanes

16. The order location-prefix-parent chaing-suffix is followed. Prefixes are used to denote the number of identical substituents attached to the parent chain. In naming alkanes, two numbers are separated by a comma, while a word and a number are separated by a dash. Naming Branched-Chain Alkanes

17. Name the branched-chain alkane shown below. Naming Branched-Chain Alkanes

18. Step 1. Find the longest continuous chain in the molecule. This will serve as the parent chain. The longest chain is composed of nine carbons. Thus, it shall have the name, nonane .

19. Step 2. Identify the alkyl groups and their positions by looking at which carbon atom they are attached. Make sure that the position will yield the lowest number for the alkyl group. In the example given, the alkyl group attached in the parent chain is methyl.

20. To locate its position, you can count either from left to right, or right to left. If the counting starts at left, methyl will be connected to carbon-4; If the counting starts at right, methyl will be connected to carbon-6. Comparing the two, the first case gives the lowest number for methyl. Step 3. Using the order location-prefix-parent chain-suffix, we write the complete name of the molecule: 4-methylnonane .

21. Draw the skeletal structure of the branched-chain alkane: 2,4-diethylhexane. Step 1. Draw the parent chain first. Drawing Branched-Chain Alkanes In the example given, the parent chain is hexane.

22. Step 2. Number the carbons in the molecule and draw and place the alkyl groups based on the locations given by the name.

23. Alkanes are usually found in natural gas, petroleum deposits, and coal. Methane (CH 4 ), also known as natural gas, is a colorless, odorless, and gaseous alkane that is mostly used as fuel for heating homes, cooking, and electricity generation. Methane is commonly found together with other fossil fuels like coal and oil. It is also considered as a greenhouse gas, with a global warming potential of 21 (which means that it can trap heat 21 times greater than carbon dioxide). Uses of Alkanes

24. Name the branched-chain alkane shown below.

25. Step 1. Find the longest continuous chain in the molecule. This will serve as the parent chain. The longest chain is composed of eight carbons, thus shall have the name octane .

26. Step 2. Identify the alkyl groups and their positions by looking at which carbon atom they are attached. Make sure that the position will yield the lowest number for the alkyl group. The alkyl groups attached to the parent chain are both methyl groups.

27. To locate its position, you can count either from left to right, or right to left. If the counting starts at left, methyl groups will be connected to carbon-4; If the counting starts at right, methyl groups will be connected to carbon-5. Comparing the two, the first case gives the lowest number for the methyl groups. Step 3. Using the order location-prefix-parent chain-suffix, we write the name of the molecule: 4,4-dimethyloctane .

28. Alkanes are a group of hydrocarbons that contain carbon-carbon single (C-C) bonds and carbon-hydrogen (C-H) bonds only. 1 Alkanes have a general formula of C n H 2n+2 where n is the number of carbon atoms (n=1, 2, 3, …). Their names end in -ane . 2 Since alkanes are the only hydrocarbons that contain purely single bonds throughout their structures, they are classified as saturated hydrocarbons . 3

29. Alkanes are insoluble in water, but are soluble in organic solvents. They are also less dense than water. 4 Generally, alkanes have low melting and boiling points. The viscosity, melting and boiling points increase as more carbon atoms are added to the alkyl chain. 5 In a condensed structure , only the symbols for carbon and hydrogen (and its subscripts) are shown while the line bonds are absent. 6

30. In a Kekule structure , the structure is drawn by explicitly writing the symbols of each atom and the bonds that exists between two atoms. 7 In a skeletal structure , the structure is represented by line segments connected through a zigzag direction. Endpoint represent carbon atoms. 8

31. Fill up the table below. Skeletal Structure of Alkane Name 2. 3. 4. 3,3,4,4-tetramethylheptane 5. 6-propyldecane

32. Given its properties, what do you think could be the other uses of alkanes?

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