Q: Chemists often determine the relative proportions of isotopes in a given sample by using a special tool called a mass spectrometer. However, at student-level chemistry, this information is often provided for you on school tests, etc., in the form of established values from scientific literature.  For our purposes, let's say we're working with the isotopes carbon-12 and carbon-13. Within a given element, different isotopes appear in different proportions. These proportions are almost always expressed as percentages. Some isotopes will be very common, while others will be very rare - at times, so rare that they can barely be detected. This information can be determined through mass spectrometry or from a reference book. Let's say that the abundance of carbon-12 is 99% and the abundance of carbon-13 is 1%. Other carbon isotopes do exist, but they exist in quantities so small that, for this example problem, they can be ignored. Multiply the atomic mass of each isotope by its percent abundance (written as a decimal). To convert a percentage to a decimal, simply divide it by 100. The converted percentages should always add up to 1.  Our sample contains carbon-12 and carbon-13. If carbon-12 makes up 99% of the sample and carbon-13 makes up 1% of the sample, multiply 12 (the atomic mass of carbon-12) by 0.99 and 13 (the atomic mass of carbon-13) by 0.01. A reference book will give percent proportions based on all the known amounts of an element's isotopes. Most chemistry textbooks include this information in a table at the end of the book. A mass spectrometer can also yield the proportions for the sample being tested. Sum the products of the multiplications you performed in the previous step. The result of this addition is the relative atomic mass of your element - the average value of the atomic masses of your element's isotopes. When discussing an element in general, and not specific isotopes of that element, this value is used. In our example, 12 x 0.99 = 11.88 for carbon-12, while 13 x 0.01 = 0.13 for carbon-13. The relative atomic mass of our example is 11.88 + 0.13 = 12.01.
A: Determine which isotopes are in the sample. Determine the relative abundance of each isotope in the sample. Multiply the atomic mass of each isotope by its proportion in the sample. Add the results.

Q: If you have recognized the criticism as completely destructive and hurtful, then you can think about why the person might have said such a thing to make yourself feel better. Maybe the girl was jealous of your new outfit and said you dress like a skank. Maybe a guy said you're not a good writer because he's jealous that you just published a story. Maybe the person was just in a bad mood and felt like taking it out on someone. Whatever the reason, remind yourself that it had little to do with who you are. Put yourself in the person's shoes. Understand where he is really coming from. Though the words will still sting, it might make you feel better. If your coworker yelled at you for no reason, but you remember that he is going through a divorce, then you'll start to be a bit more understanding, won't you? Okay, so maybe the criticism was delivered in a way that was completely mean, unnecessary, and hurtful, and most of the things that were said were way off base. Maybe your co-worker said you were "a complete mess" or your friend said you were "totally selfish" for what you think was no reason at all. Take a minute to think about it, though: do you need to brush up on your organizational skills? Have you been known to be a little selfish from time to time? If so, then maybe you should reconsider your actions without getting hurt by the way the criticism was given. Sure, it's very hard to take someone seriously if they are yelling at you, calling you names, or generally treating you with completely disrespect. This makes it nearly impossible to take a word they say seriously. But if you want to be the bigger person, try to find the underlying message if there is one. What was that thing your mother told you about "sticks and stones" not being able to break your bones? Sure, you thought it was stupid in third grade, but now, you're a lot older, and it's starting to make sense. In the end, destructive criticism isn't made up of bullets, swords, or atomic bombs -- it's just a series of words connected together in a way designed to make you feel terrible. So, remind yourself that criticism only consists of a bunch of words. Criticism can't steal your money, slap you across the face, or crash your car. So don't let it get to you. The most important thing you can do is maintain your confidence. No matter what people are saying about you, you have to stay strong, remember who you are, and not let other people influence your own self-worth. Being confident doesn't mean thinking that you're flawless, but it does mean loving who you are and how you look. If you're truly confident, then you won't let haters get you down and make you think less of yourself.  If you're unhappy with who you are, ask yourself why. Make a list of a few things you don't like about yourself and figure out what you can change. Being confident also means accepting the things you cannot change about yourself. So, you don't like that you're so tall. Do you plan on slouching for the rest of your life, or will you start to love your long legs after all? Hanging out with people who make you feel good about yourself will also go a long way in making you feel more confident. If you're hanging with people who always bring you down, then yeah, you're not going to feel good about yourself. So...you've heard that someone said you're a brown-noser. Will you start participating less in class? Or your co-worker has told you you're too type A. Are you going to stop being who you are if it's working for you? Of course not. If you haven't received a valid criticism and know that what people are telling you is only only being said because of jealousy, anger, or mean-spiritedness, then there's no need to change your routine to please people.  If the criticism has no basis whatsoever, then the best thing you can do is to ignore it completely.  Don't feel bad if you're not able to push all of these negative words aside right away. It takes practice to stop caring about what people think.
A:
Understand the person's true motives. Look for the grain of truth. Remember that words can never hurt you. Stay confident. Keep doing what you're doing.