![]() All isotopes of an element have the same number of protons and electrons, which means they exhibit the same chemistry. Atoms that have the same number of protons, and hence the same atomic number, but different numbers of neutrons are called isotopes. Unlike protons, the number of neutrons is not absolutely fixed for most elements. Recall that the nuclei of most atoms contain neutrons as well as protons. Hence, the atomic number defines the element in question. If you change the atomic number to 12, you are no longer dealing with sodium atoms, but magnesium atoms. That means that all sodium atoms have 11 protons. For example, the atomic number (z) for sodium (Na) is 11. The symbol for the atomic number is designated with the letter Z. This number is known as the atomic number, which identifies the number of protons in the nucleus of ALL atoms in a given element. When you study the periodic table, the first thing that you may notice is the number that lies above the symbol. Again, the mass of a mole substance is called the molar mass, and to find the molar mass of a substance you just need a periodic table and the chemical formula.\) That’s the total molar mass of the compound CO2. Then finally you add all products, so 12 plus 32 is 44. You would multiply it by its subscript of 2, which is 32. Then you’d do the same thing with oxygen. Then the way you would find that is first you would find the atomic mass of carbon, which is 12, and then you’d multiply it by the subscript, which is just an understood 1 right there, so the product there would be 12. ![]() If you were trying to find the molar mass of the compound carbon dioxide, which looks like this-CO2-and the molar mass is 44. Then, to find the molar mass of the compound, you’re going to add all those products together. By multiplying the atomic mass by the subscript you’re getting the product, you’re getting the molar mass product for that atom. That way, you’re finding the total molar mass for all of that atom because you’re finding the atomic mass, then you’re multiplying it by however many times it appears in the compound. After you’ve found the atomic mass, multiply the atomic mass by the subscript. You’re going to start with one atom at a time. I’m going to show you a 3-step process for finding the molar mass of a compound.įirst, find the atomic mass of an atom. You kind of follow the same protocol for finding the molar mass of an element, but then you combine all those molar masses together to find the molar mass of the compound. Now the molar mass of a compound can be calculated by summing the molar masses of each atom and the chemical formula. That’s how you find the molar mass of an element. Now we’ll write it with a different unit because it’s also our molar mass, and that will be grams over moles: \(\frac\). If you’re looking at the element of copper you would look in the periodic table and find that it has an average atomic mass of 63.55 AMU, so that’s the molar mass. If you’re trying to find the molar mass of an element, then you’ll take the average atomic mass listed in the periodic table. To calculate the molar mass of a substance you need a periodic table and the chemical formula. The mass of a mole of substance is called the molar mass.
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