* Chemical Formula: A compound's formula tells you the ratio of atoms of each element present. For example, water (H₂O) always has two hydrogen atoms for every one oxygen atom.

* Atomic Mass: Each element has a specific atomic mass. This mass is constant for that element.

* Proportions: The mass of each element in a compound is determined by the ratio of atoms in the formula and the atomic mass of each element.

Example:

Let's take water (H₂O) again.

* Atomic mass of hydrogen (H): 1 atomic mass unit (amu)

* Atomic mass of oxygen (O): 16 amu

In one molecule of water:

* Mass of hydrogen: 2 H atoms * 1 amu/H atom = 2 amu

* Mass of oxygen: 1 O atom * 16 amu/O atom = 16 amu

Therefore, the mass ratio of hydrogen to oxygen in water is 2:16, or simplified, 1:8.

Amount of Compound:

* More compound, more mass: If you have more water, you'll have more hydrogen and oxygen atoms, and therefore, a greater mass of each element.

* Less compound, less mass: If you have less water, you'll have fewer hydrogen and oxygen atoms, and therefore, a smaller mass of each element.

Conclusion:

The mass of each element in a compound is directly proportional to the amount of the compound present. The ratio of elements within the compound remains constant, but the total mass of each element changes with the quantity of the compound.