![]() This is not the same as molecular mass, which is the mass of a single molecule of well-defined isotopes. This is how to calculate molar mass (average molecular weight), which is based on isotropically weighted averages. The atomic weights used on this site come from NIST, the National Institute of Standards and Technology. The formula weight is simply the weight in atomic mass units of all the atoms in a given formula. When calculating molecular weight of a chemical compound, it tells us how many grams are in one mole of that substance. The percentage by weight of any atom or group of atoms in a compound can be computed by dividing the total weight of the atom (or group of atoms) in the formula by the formula weight and multiplying by 100.įinding molar mass starts with units of grams per mole (g/mol). If the formula used in calculating molar mass is the molecular formula, the formula weight computed is the molecular weight. Using the chemical formula of the compound and the periodic table of elements, we can add up the atomic weights and calculate molecular weight of the substance. This site explains how to find molar mass. The reason is that the molar mass of the substance affects the conversion. To complete this calculation, you have to know what substance you are trying to convert. These relative weights computed from the chemical equation are sometimes called equation weights.Ī common request on this site is to convert grams to moles. You could’ve done this without the intervening equation simply by substituting the name of the metal ions, calcium with cesium.In chemistry, the formula weight is a quantity computed by multiplying the atomic weight (in atomic mass units) of each element in a chemical formula by the number of atoms of that element present in the formula, then adding all of these products together.įormula weights are especially useful in determining the relative weights of reagents and products in a chemical reaction. Therefore, when calcium reacts with cesium in a displacement reaction, the products of the reaction are calcium oxide and cesium. Or, to put it another way, the calcium has displaced the cesium. In this reaction, oxygen has migrated from cesium over to calcium. The second product of this reaction is pure cesium. Therefore, only one equivalent of calcium two plus is required to counterbalance the negative charge of oxygen two minus. Calcium has two electrons in its outer shell and is therefore in group two and forms calcium two plus ions. One of the products of this reaction is calcium oxide. In the compound cesium oxide, we need two equivalents of cesium in order to counteract the two minus charge of the oxide, giving us the formula Cs2O. ![]() It has six electrons in its valence shell and can gain two more to form an octet, forming oxygen two minus. Oxygen, on the other hand, is in group 16. ![]() This means it has one electron in its outer shell and forms ions with a single positive charge. If you look at your periodic table, you’ll see that cesium is in group one. Calcium has the symbol Ca while cesium oxide has the symbol Cs2O. In this case, the reactants are calcium and cesium oxide. You can also get something called a double displacement, where two groups from two different compounds swap with one another. In this example, the group B is being replaced by C. What are the products of the reaction?Ī displacement reaction is a reaction where one group of a compound is replaced by another, like this. When calcium reacts with cesium oxide, a displacement reaction occurs.
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