The atomic mass of an element is the mass of one atom of that element, expressed in atomic mass units (amu). On the other hand, the molar mass of an element is the mass of one mole of that element, expressed in grams per mole (g/mol).
The numerical value of the atomic mass of an element is equal to the molar mass of that element. This is because the atomic mass unit (amu) is defined based on the carbon-12 isotope, which has a mass of exactly 12 grams per mole. This means that the atomic mass of carbon-12 is numerically equal to its molar mass, which is 12 g/mol.
The atomic mass of other elements is determined relative to carbon-12 using a scale called the atomic mass scale or the unified atomic mass unit (u). For example, the atomic mass of oxygen is approximately 16 u, which means that one atom of oxygen is about 16 times heavier than one-twelfth the mass of a carbon-12 atom.
Since the atomic mass of an element is defined relative to the atomic mass of carbon-12, which is equal to its molar mass, the numerical value of the atomic mass of an element is also equal to its molar mass. This holds true for all elements and allows us to directly convert between atomic mass and molar mass using the same numerical value.