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Naming Hydrocarbons. Carbon to hydrogen ratios. Vocabulary. Hydrocarbon- a molecule that contains only hydrogen and oxygen bonds. A hydrocarbon is a special binary molecular compound. Alkane- A hydrocarbon that is saturated.
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Naming Hydrocarbons Carbon to hydrogen ratios
Vocabulary • Hydrocarbon- a molecule that contains only hydrogen and oxygen bonds. A hydrocarbon is a special binary molecular compound. • Alkane- A hydrocarbon that is saturated. • Saturated-when a hydrocarbon contains the maximum number of hydrogens.
Pattern recognition (easy) • Look at the numbers below. Find the pattern in your group. Predict the final number. • 2 • 4 • 6 • 8 • ??
Pattern recognition (easy) • Look at the numbers below. Find the pattern in your group. Predict the final number. • 2 • 4 • 6 • 8 • 10
Pattern recognition (medium) • Look at the numbers below. Find the pattern in your group. Predict the final number. • 1 • 4 • 9 • 16 • 25 • ??
Pattern recognition (medium) • Look at the numbers below. Find the pattern in your group. Predict the final number. • 1 • 4 • 9 • 16 • 25 • 36 (6 squared)
Pattern recognition (tricky) • Look at the numbers below. Find the pattern in your group. Predict the final number. • x+10y • 2x+8y • 3x+6y • 4x+4y • ??
Pattern recognition (tricky) • Look at the numbers below. Find the pattern in your group. Predict the final number. • x+10y • 2x+8y • 3x+6y • 4x+4y • 5x+2y
Do you notice a pattern? • CH • C2H4 • C3H9 • C4H16 • C5H25 • C6H36 • C7H49 • C8H64 • C10H? • Can you come up with a math mathematical equation that relates the number of carbons to the number of hydrogens? • CxH? • What is the relationship between carbon and hydrogen?
Do you notice a pattern? • CH • C2H4 • C3H9 • C4H16 • C5H25 • C6H36 • C7H49 • C8H64 • C10H? • Can you come up with a math mathematical equation that relates the number of carbons to the number of hydrogens? • CxHx^2 • The ? = x2
Do you notice a pattern? • CH4 • C2H6 • C3H8 • C4H10 • C5H12 • C6H14 • C7H16 • C8H18 • C10H? • Can you come up with a mathematical relationship between the number of carbons and the number of hydrogens? • C20H? • C83H?
Do you notice a pattern? • CH4 • C2H6 • C3H8 • C4H10 • C5H12 • C6H14 • C7H16 • C8H18 • C10H22 • Can you come up with a mathematical relationship between the number of carbons and the number of hydrogens? • C20H42 • C83H168
Alkanes • In an alkane the number of hydrogens is twice that of the carbons plus two. • Recall • CH4 • C2H6 • C3H8 • C4H10 • Note: if you double the number of carbons and then add two you get the number of hydrogens.
Naming alkanes • Since the number of hydrogens depends on the number of carbons, alkanes are named by the number of carbons present. See right. Just like with binary molecular, a prefix system is used.
Naming alkanes • When ever you wish to name an alkane (or any hydrocarbon for that matter) you must first look at the number of carbons present. • The number of carbons present ALWAYS tells you what prefix to use • Examples • CH4 is METHane • C5H12 is PENTane • C7H16 is HEPTane • CxH2x+2 Note: all alkanes end in “ane”
Practice • Go back to the website and practice the first two html file: “Name to formula, alkanes” and “Formula to names, alkanes”. • Since there are only ten alkanes that with prefixes that I want you to memorize, this is a very easy skill and as such shouldn’t take you long. • Once you’ve mastered this skill complete this PowerPoint.
Alkanes, alkenes and alkynes • The good news is you don’t need to memorize anymore prefixes. The ones to the right are all you need. • The bad news is you are going to need to do just a little math.
Alkanes, alkenes and alkynes • As with alkanes, the number of carbons dictates the prefix. However, alkenes and alkynes have different numbers of hydrogens. • Propane = C3H8 (CxH2x+2) • Propene = C3H6 (CxH2x) • If a hydrocarbon has exactly twice as many hydrogens as it does carbons then it is an “alkene”. Note: the last three letters are all that changes.
Alkenes vs. alkynes • With an alkyne the number of hydrogens is double the number of carbons minus two. • CxH2x-2 • Propyne = C3H4 • Whenever confronted with a compound made up of ONLY carbon and hydrogen, always compare the number of hydrogens and carbons.
Which hydrocarbon am I??? • Alkane: If your number of hydrogens is two more than twice the number of carbons you’re an alkane.(e.g. C4H10, C8H18) • Alkene: If your number of hydrogens is exactly twice the number of carbons you’re an alkene.(e.g. C4H8, C8H16) • Alkyne: If your number of hydrogens is two LESS than twice the number of carbons you’re an alkyne.(e.g. C4H6, C8H14)
Practice • I know that we were light on the examples with the alkene and alkynes. • Work on the hydrocarbon scramble practice html file. There will be additional help buttons if you can’t figure it out.