THE ALKANESsingle bonded hydrocarbon chains

Tahoma Jr. High8th Grade ScienceMaple Valley, WA

hydrogen gaswater

oxygen gas

How many of you spilled

H2O on your worksheet ?

You need to know chemistry

formulas to know this one…

H2O2 (get it?)is hydrogen

pyroxide

(which you use to sterilize wounds)

ring

OZONE O3

ozone “hole” getting bigger from 1970s to 1990s(not clear if pollution ban in the 1980s is working yet or not)

carbon dioxide gas

you exhalecarbon dioxide

ALKANES ARE FUELSFuels are energy rich molecules – energy is stored in the bonds and released when the bonds are broken.

You need three things to make a fire:

FUEL (wood, oil, coal, natural gas, etc.)

and…?

OXYGEN – to break the fuel downand…?

Heat (or ignition source) – to start the chemical reaction to break down the fuel – once this happens, the reaction can run on its own (spark, pilot light, etc.)

wood AND sugar inmarshmallows arecarbohydrate fuels

methane = CH4 (real “natural” gas)

Cows belch and fart LOTS of methane

Cows are NOT environmentally friendly !

Cows produce about one poundof methane for every two poundsof meat they make/yield.An average cow burps about 280 liters (70 gallons) of methane daily.

Methane emissions from livestock (especially cows) contribute significantly to greenhouse gases.

Methane is over 25 times more potent a Greenhouse Gas than carbon dioxide, but there is thankfully

much less of it in the atmosphere. Still…

ethane = C2H6 (basic building block for plastics such as polyethylene, or an alcohol gasoline fuel extender called ethanol)

Ethanol is typical “drinking” alcohol made from sugar sources –

and burns clean. Too much though can harm a regular engine.

propane = C3H8

(common fuel gas, liquid under pressure)

Metal container for higher pressures

butane = C4H10

(also a fuel gas, but more easily stays liquid)Plastic container for

lower pressures

pentane = C5H12 (uncommon liquid fuel)

* will not be on test: hexane = C6H14

* will not be on test: heptane = C7H16

octane = C8H18(gasoline additive, long chain actually slows down the burn

to be more complete/powerful and efficient)

87, 89 and 93 octane levels of gasoline

Crude oil is thick because oflong hydrocarbon chains being tangled together. A refinery “cracking” tower allows you to “cut” and sort them from lightest (short) chains at the top that boil off first, to…

then medium length chains taken out further down…

leaving just the longest chains at the bottom which is like “sludge”.

propane

octane (gasoline)

asphalt for roads

methane

a bit longer chains below that…

On the upcoming Test you should know how alkanes are put together and know

the formulas for:

methane to pentaneand octane

Can you see a pattern making it easy to figure out how many hydrogens would be in a 20 carbon alkane?

1

2

3

4

5

8

Here’s why you learn algebra, because a simple formula can figure out ALL the alkanes:

Think about how they are put together…

Each carbon has at least 2 hydrogens – and the end carbons each have another as “bookends” to close off the chain at each

end.Would this formula work?

2n+2 (n = # of carbons)So… what would the formula be for a 20 carbon alkane?

C20H____?C20H42

Now you know about how some “hydrocarbons” are put together and use a logical naming system in

most cases to help remember them.

A little mnemonic to help is:

“alkanes Make Explosions Pretty Big”(methane, ethane, propane, butane)

Once you get to Pentane (5) is fairly easy if you know the prefixes.

What would C10H22 be called?

Think about it… Yup… decane !!(decade = 10)

And finally… what if there were double bonds between the carbons?

(like we saw in the O2 gas molecule)

Organic chemistry calls that group of double-bonded hydrocarbons “alkenes”

and triple-bonded ones are “alkynes”

Organic chemistry has some basic rules that help make sense out of the millions of organic chemicals

around.Alkenes and alkynes won’t be on a test, but we thought we should show you that science does try to make things easier, but you HAVE TO KNOW THE

BASICS FIRST!!learn those six alkane names and formulas -

a flashcard for each would be VERY helpful !!end show