The atomic mass of an element is determined by the combined mass of its protons, neutrons, and electrons. Protons and neutrons contribute significantly to the atomic mass, while electrons, being much lighter, contribute only a negligible amount.
To compare the atomic masses of different elements, you can consult the periodic table. Each element is listed with its atomic number and atomic mass. The atomic number represents the number of protons in an atom of that element, while the atomic mass is usually given as an average value, taking into account the naturally occurring isotopes and their relative abundances.
Generally, atomic masses increase as you move from left to right and from bottom to top across the periodic table. This is because the number of protons and neutrons generally increases, resulting in a higher atomic mass. However, there are some exceptions due to the presence of isotopes with different masses.
It's important to note that atomic mass is not the same as atomic weight or molar mass. Atomic weight is the weighted average of the atomic masses of all the naturally occurring isotopes of an element, taking into account their relative abundances. Molar mass, on the other hand, is the mass of one mole of atoms of a particular element and is numerically equal to the atomic weight.
In summary, to determine which element has a higher atomic mass, you can compare the atomic masses listed on the periodic table, keeping in mind that atomic mass generally increases from left to right and from bottom to top, but there may be exceptions due to isotopic variations.