Significant figures!?

Question

Two atoms in a molecule are 120 picometers apart. What is the distance in nanometers? 1 meter = 10^12 picometers. 1 meter = 10^9 nanometers. I got .12 but it says I have the wrong number of significant figures. Any help? Thanks :)

Answer 1

The thing that says you have the wrong number of significant figures is kind of screwed up. Technically, 120 picometers has only 2 significant digits because the 0 in 120 isn't significant, but whatever you're working with assumes that the 0 is significant. Basically, your answer should be .120 not .12

If you know about significant digits that would make sense, but if you don't, let me explain something very briefly that will help you with your questions.

Look at the numbers that they give you in the problem. Make sure that your answer has the name number of digits written out as the shortest one in your question. So, in this question, 120 has 3 digits. That means your answer has to also have 3 digits: 0.120 (the 0 before the decimal doesn't count). 0.12 only has 2 digits, so you have to add the 0 at the end to show that you are accurate enough to know that it really is exactly 0.120 and not 0.121 but is rounded to 0.12.

Make sure that your answer has the name number of digits written out as the shortest one in your question. This isn't entirely correct, but it's probably good enough to help you with your homework.

if you want to read up more, check this out
http://www.usca.edu/chemistry/genchem/sigfig.htm

Answer 2

More accurately it would be 0.12 nanometers. Always need the 0 befere the decimal point.