single bonded hydrocarbon chains THE ALKANES single bonded hydrocarbon chains Tahoma Jr. High 8th Grade Science Maple Valley, WA

hydrogen gas water 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)

ozone “hole” getting bigger from 1970s to 1990s 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 exhale carbon dioxide

ALKANES ARE FUELS FUEL (wood, oil, coal, natural gas, etc.) Fuels 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…? wood AND sugar in marshmallows are carbohydrate fuels OXYGEN – to break the fuel down and…? 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.)

methane = CH4 (real “natural” gas) Cows belch and fart LOTS of methane

Cows are NOT environmentally friendly ! 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… Cows produce about one pound of methane for every two pounds of meat they make/yield. An average cow burps about 280 liters (70 gallons) of methane daily.

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.

Metal container for higher pressures propane = C3H8 (common fuel gas, liquid under pressure) Metal container for higher pressures

Plastic container for lower 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 of methane Crude oil is thick because of long 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… propane a bit longer chains below that… octane (gasoline) then medium length chains taken out further down… leaving just the longest chains at the bottom which is like “sludge”. asphalt for roads

On the upcoming Test you should know how alkanes are put together and know the formulas for: methane to pentane 1 2 3 4 5 and octane Can you see a pattern making it easy to figure out how many hydrogens would be in a 20 carbon alkane? 8

Would this formula work? 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

A little mnemonic to help is: “alkanes Make Explosions Pretty Big” 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