SILICON AVERAGE ATOMIC MASS PLUS

For this problem, if our answer were below 28 or above 30, we would know that we had made an error. In addition, it is not possible for the average massive of an atom in the sample to be lighter than the lightest atom or heavier than the heaviest atom. If your final answer ends up being closer to the mass of an isotope with a relatively small abundance, you may have made a mistake along the way. This information can be valuable to keep in mind when checking your answer.

It makes sense that since we’re finding the average mass of an atom in a sample of many atoms, the more silicon-28 atoms there are, the closer to 28 the average is going to be. Note that of the three mass numbers of the isotopes, 28, 29, and 30, our final answer, 28.1, is closest to 28, the mass number of the isotope with the highest abundance. Interestingly, relative atomic mass does not take a unit. Rounded to one decimal place, as the question indicates, our final answer becomes 28.1. However, that is the decimal for 30 percent. It is a common error for students at this point in the problem to accidentally write three percent as 0.3. As we carry out the calculations, it’s important to remember that three percent as a decimal is 0.03. We know that we’re incorporating all of the isotopes of silicon because our percentages add up to 100 percent in total.

SILICON AVERAGE ATOMIC MASS PLUS

We can insert the numbers from this problem as such: 92 percent times 28 plus five percent times 29 plus three percent times 30. As long as the percent isotopic abundances of the different isotopes add up to 100 percent, we can incorporate any number of them into the formula. If there are four isotopes present, we can simply include an additional isotopic abundance and mass of isotope for the fourth isotope.

In other problems, if there’s only, say, two isotopes, we can simply omit the percent isotopic abundance and the mass of isotope three. Note that this general formula will work for different numbers of isotopes as well. The relative atomic mass equals the percent isotopic abundance of isotope one times the mass number of isotope one plus the percent isotopic abundance of isotope two times the mass number of isotope two plus the percent isotopic abundance of isotope three times the mass number of isotope three. In order to calculate the relative atomic mass of an element, we need to set up an equation that incorporates the abundances of its different isotopes as well as their mass numbers. As we’ve already discussed, in a sample of an element, the different isotopes will have different abundances and atoms of those isotopes will have different masses.

The last key term, the relative atomic mass of an element, refers to the average mass of an atom in a sample of that element. The numbers in this problem more specifically mean that in a sample of silicon, 92 percent of the atoms will be silicon-28 atoms, five percent of the atoms will be silicon-29 atoms, and three percent of the atoms will be silicon-30 atoms. The next key term, isotopic abundance, refers to the relative number of atoms of each isotope you will find in a sample of the element. Atoms of silicon-28, silicon-29, and silicon-30 have 14, 15, and 16 neutrons, respectively. Since a proton and a neutron each weigh one unified atomic mass unit, adding the number of protons and the number of neutrons in an atom of an isotope gives us the mass number of the isotope, which can be found in its name.

Where they differ is in their number of neutrons. Since silicon is element number 14 on the periodic table, we know that atoms of each of these three isotopes have 14 protons. The number following silicon refers to the mass number of that isotope, which is the number of protons and the number of neutrons in the nucleus of atoms of that isotope added together. The three isotopes that we’re dealing with in this problem are silicon-28, silicon-29, and silicon-30. This question is talking about isotopes, which are versions of an element whose atoms have the same number of protons but different numbers of neutrons. What is the relative atomic mass of silicon to one decimal place?īefore we set up the equation to calculate the relative atomic mass of silicon, let’s go over some key terms in this question. Their isotopic abundances are 92 percent, five percent, and three percent, respectively. Silicon exists as three isotopes: silicon-28, silicon-29, and silicon-30.

Silicon average atomic mass