Naming Hydrocarbons

Carbon to hydrogen ratios

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.

Vocabulary

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 (easy)

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 (medium)

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

Pattern recognition (tricky)

CH C2H4 C3H9 C4H16 C5H25 C6H36 C7H49 C8H64 C10H?

Do you notice a pattern? 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?

CH C2H4 C3H9 C4H16 C5H25 C6H36 C7H49 C8H64 C10H?

Do you notice a pattern? Can you come up with a math

mathematical equation that relates the number of carbons to the number of hydrogens?

CxHx^2

The ? = x2

CH4 C2H6 C3H8 C4H10 C5H12 C6H14 C7H16 C8H18 C10H?

Do you notice a pattern? Can you come up with a

mathematical relationship between the number of carbons and the number of hydrogens?

C20H?C83H?

CH4 C2H6 C3H8 C4H10 C5H12 C6H14 C7H16 C8H18 C10H22

Do you notice a pattern? Can you come up with a

mathematical relationship between the number of carbons and the number of hydrogens?

C20H42C83H168

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.

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 alkanesNumber of carbons

Prefix

1 meth

2 eth3 prop4 but5 pent6 hex

7 hept8 oct9 non10 dec

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”

Naming alkanes

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.

Practice

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 Number

of carbons

Prefix

1 meth

2 eth3 prop4 but5 pent6 hex

7 hept8 oct9 non10 dec

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.

Alkanes, alkenes and alkynes Number

of carbons

Prefix

1 meth

2 eth3 prop4 but5 pent6 hex

7 hept8 oct9 non10 dec

With an alkyne the number of hydrogens is double the number of carbons minus two.◦ CxHx-2

◦ Propyne = C3H4

Whenever confronted with a compound made up of ONLY carbon and hydrogen, always compare the number of hydrogens and carbons.

Alkenes vs. alkynesNumber of carbons

Prefix

1 meth

2 eth3 prop4 but5 pent6 hex

7 hept8 oct9 non10 dec

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)

Which hydrocarbon am I???

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.

Practice