Al+3 + Cl- - AlCl3 I can't draw the lewis structure here, but it should have 3 bonds and 24 electrons(no lone pairs)It's a non-polar molecule.
News FlashChrome moly IS steel- it is short for chrome molybdenum which is a steel alloy, and for all practical purposes they weigh exactly the sameThe difference is that chrome moly is stronger- because of this the tubes can be made thinner and still maintain the strengthLess materialless weightNews Flash (2)Just because a frame might be made of aluminum doesn't mean it is lighter than steelIt is a fact that aluminum is 1/2 the weight of steel but it is also 1/3 the strengthTo improve the strength more material must be added (and/or intensive engineering employed) therefore making an aluminum frame as strong as steel will end up weighing about the sameNews Flash (3)there are premium steels out there today that rival the weight of titanium and carbon fiber and maintain the strength, and many of these steels are still less expensive than either of themPracticality has everything to do usage, and you didn't mention how you were using the bikeAdd some more detail and you'll get a better answer.
It sounds like you aren't out to break the bank on a new bikeSo it will most likely be an aluminum frame unless you are planning to pay more than your question seems to indicateIt could also be a steel frame if you get an older used road or mountain bikeIf you are using the bike to get around a fairly short distance, focus on the features you want and the price you are willing to pay, not the material it is made ofIf you are going to use the bike a great amount or ride longer distances then it might be worth thinking about frame materialFor most everyday riders using a bike to get around, frame material really doesn't matter that muchIt just gives us bike enthusiasts something to argue aboutBelow is a link that summarizes the different materials fairly wellKeep in mind as you read about how a material feels it is fairly subtle unless you spend a lot of time on a bike.
I agree with MR that the design of the bike has more to do with it's weight than the material chosenYou can easily buy a 30 aluminum bikeYikes! High tensile steel cheap, heavy CrMo quality, more costly steel, can be made into great bikes 953 Stainless steel stronger than titanium, expensive, will be custom bike True Temper S3 similar toughness, less costly than 953, and not stainless Al light, less durable, but can be high value if designed correctly Just remember if you go steel to keep it covered and/or paintedUnfortunately with the exception of 953 there are no other current stainless steel tubes on the marketThat said, a little care can make the bike last long, long timeMy dad still has his 70+ year old Raleigh.
Both materials are excellent and practicalWhile both can be made into light frames, aluminum tends to be lighterThat being said there are plenty of cheapo alumbikes sold at discount stores that are very heavySo it's not just the material but the design and quality of the frame that makes a big difference.