Molecular weight, also known as molecular mass or molar mass, is a measure of the mass of a single molecule of a chemical compound. It is usually expressed in atomic mass units (amu) or grams per mole (g/mol).
The molecular weight of a compound is calculated by adding up the atomic weights of all of the atoms in the molecule. The atomic weight of an element is listed on the periodic table of elements and is the average mass of an atom of that element relative to the mass of a carbon-12 atom, which is defined as 12 amu.
For example, the molecular weight of water (H2O) is 18.015 g/mol. This is calculated by adding the atomic weights of 2 hydrogen atoms (2 * 1.0079 amu) and 1 oxygen atom (15.9994 amu), for a total of 18.0153 amu.
Molecular weight is an important property of a chemical compound because it influences the physical and chemical properties of the compound. For example, compounds with a high molecular weight tend to have a higher boiling point and a lower vapor pressure than compounds with a low molecular weight.
In addition to its role in characterizing the physical and chemical properties of compounds, molecular weight is also used in many fields, including chemistry, biology, and engineering, to calculate the amount of a substance needed for a particular reaction or application.
To calculate the molecular weight of a chemical compound, you can use the following formula:
Molecular Weight = (sum of atomic weights of all atoms in the compound)
The atomic weight of each element is listed on the periodic table of elements, and is usually expressed in atomic mass units (amu). For example, the atomic weight of carbon is 12.0107 amu, and the atomic weight of oxygen is 15.9994 amu.
To use the formula, simply add up the atomic weights of all of the atoms in the compound. For example, to calculate the molecular weight of water (H2O), you would add the atomic weights of 2 hydrogen atoms (2 * 1.0079 amu) and 1 oxygen atom (15.9994 amu), for a total of 18.0153 amu.
It’s important to note that the molecular weight of a compound is not the same as its mass. The molecular weight is a measure of the mass of a molecule, whereas the mass of a compound is the sum of the masses of all of its atoms.