How to Calculate Atomic Mass

How to Calculate Atomic Mass You may be asked to calculate atomic mass in chemistry or physics. There is more than one way to find atomic mass. Which method you use depends on the information youre given. First, its a good idea to understand what exactly, atomic mass means. What Is Atomic Mass? Atomic mass is the sum of the masses of the protons, neutrons, and electrons in an atom, or the average mass, in a group of atoms. However, electrons have so much less mass than protons and neutrons that they dont factor into the calculation. So,  the atomic mass is the sum of the masses of protons and neutrons. There are three ways to find atomic mass, depending on your situation. Which one to use depends on whether you have a single atom, a natural sample of the element, or simply need to know the standard value. 3 Ways to Find Atomic Mass The method used to find atomic mass depends on whether youre looking at a single atom, a natural sample, or a sample containing a known ratio of isotopes: 1) Look Up Atomic Mass on the Periodic Table If its your first encounter with chemistry, your instructor will want you to learn how to use the periodic table to find the atomic mass (atomic weight) of an element. This number usually is given below an elements symbol. Look for the decimal number, which is a weighted average of the atomic masses of all the natural isotopes of an element. Example:  If you are asked to give the atomic mass of carbon, you first need to know its element symbol, C. Look for C on the periodic table. One number is carbons element number or atomic number. Atomic number increase as you go across the table. This is not the value you want. The atomic mass or atomic weight is the decimal number, The number of significant figures varies according to the table, but the value is around 12.01. This value on a periodic table is given in atomic mass units or amu,  but for chemistry calculations, you usually write atomic mass in terms of grams per mole or g/mol. The atomic mass of carbon would be 12.01 grams per mole of carbon atoms. 2) Sum of Protons and Neutrons for a Single Atom To calculate the atomic mass of a single atom of an element, add up the mass of protons and neutrons. Example: Find the atomic mass of an isotope of carbon that has 7 neutrons. You can see from the periodic table that carbon has an atomic number of 6, which is its number of protons. The atomic mass of the atom is the mass of the protons plus the mass of the neutrons, 6 7, or 13. 3) Weighted Average for All Atoms of an Element The atomic mass of an element is a weighted average of all the elements isotopes based on their natural abundance. It is simple to calculate the atomic mass of an element with these steps.Typically, in these problems, you are provided with a list of isotopes with their mass and their natural abundance either as a decimal or percent value. Multiply each isotopes mass by its abundance. If your abundance is a percent, divide your answer by 100.Add these values together. The answer is the total atomic mass or atomic weight of the element. Example: You are given a sample containing 98% carbon-12 and 2% carbon-13. What is the relative atomic mass of the element? First, convert the percentages to decimal values by dividing each percentage by 100. The sample becomes 0.98 carbon-12 and 0.02 carbon-13. (Tip: You can check your math by making certain the decimals add up to 1. 0.98 0.02 1.00). Next, multiply  the atomic mass of each isotope by the proportion of the element in the sample: 0.98 x 12 11.760.02 x 13 0.26 For the final answer, add these together: 11.76 0.26 12.02 g/mol Advanced Note: This atomic mass is slightly higher than the value given in the periodic table for the element carbon. What does this tell you? The sample you were given to analyze contained more carbon-13 than average. You know this because your relative atomic mass is higher than the periodic table value, even though the periodic table number includes heavier isotopes, such as carbon-14. Also, note the numbers given on the periodic table apply to the Earths crust/atmosphere and may have little bearing on the expected isotope ratio in the mantle or core or on other worlds. Over time, you may notice the atomic mass values listed for each element on the periodic table may change slightly. This happens when scientists revise the estimated isotope ratio in the crust. In modern periodic tables, sometimes a range of values is cited rather than a single atomic mass. Find More Worked Examples

The Origin of the Popsicle

The Origin of the Popsicle The Popsicle was invented by an  11-year-old boy in 1905, and it was a fluke. Young Frank Epperson didn’t set out to create a treat that would keep kids happy and cool on summer days for generations to come. He mixed some soda powder and water in a glass with a small wooden stirrer, then adventure called and he wandered off and forgot about his drink. It remained outside overnight.   A Cold San Francisco Night It was cold in the San Francisco Bay area that night. When Epperson went outside the next morning, he discovered the first-ever Popsicle waiting for him, trapped frozen inside its glass. He ran the glass under hot water and was able to pull the icy treat out using the stirrer. He licked the frozen treat off the stirrer and decided it was pretty good. History was made and an entrepreneur was born. Epperson  named the treat an Epsicle, taking credit where it was due, and began selling them around the neighborhood.   Beyond the Neighborhood Fast-forward 18 years to 1923. Epperson saw a bigger and better future for his Epsicle and he applied for a patent for his frozen ice on a stick.† He described the treat as a â€Å"frozen confection of attractive appearance, which can be conveniently consumed without contamination by contact with the hand and without the need for a plate, spoon, fork, or another implement.† Epperson recommended birch, poplar, or wood-bass for the stick. Now a grown man with children of his own, Epperson deferred to their judgment and renamed the treat Popsicle, as in â€Å"Pop’s Sickle.† He moved beyond the neighborhood and began selling his Popsicles at a California amusement park. A Not-So-Happy Ending Unfortunately, Epperson’s Popsicle business failed to thrive – at least for him personally. He fell on hard times in the late 1920s and sold his Popsicle rights to the Joe Lowe Company of New York. The Lowe Company took the Popsicle to national fame with more success than Epperson had enjoyed. The company added a second stick, effectively creating two Popsicles stuck together and selling this double-sized version for a nickel. It’s rumored that approximately 8,000 were sold on just one hot summer day at Brooklyn’s Coney Island. Then Good Humor decided all this was an infringement of its own copyright for ice cream and chocolate sold on a stick. A series of lawsuits ensued with the court ultimately deciding that the Lowe Company had the right to sell frozen treats made from water while Good Humor could continue to sell its â€Å"ice cream pops.† Neither side was particularly pleased with the decision. Their feud continued until 1989 when Unilever purchased Popsicle and, subsequently, Good Humor, joining the two brands under one corporate roof. Unilever continues to sell Popsicles to this day – an estimated two billion of them a year in flavors as exotic as mojito and avocado, although cherry still remains the most popular. The double-stick version is gone, however. It was eliminated in 1986 because it was too messy and more difficult to eat than Epperson’s initial accidental brainstorm.