Here's why:
* Atomic Number: This represents the number of protons in an atom's nucleus. It defines the element itself.
* Atomic Mass: This is the average mass of an atom of an element, taking into account the different isotopes (atoms of the same element with different numbers of neutrons).
The key difference: While atomic number only accounts for protons, atomic mass considers both protons and neutrons.
Example:
* Carbon has an atomic number of 6 (6 protons).
* The most common isotope of carbon has 6 neutrons, making its atomic mass approximately 12 (6 protons + 6 neutrons).
* However, there are other isotopes of carbon, like carbon-14, which has 8 neutrons, making its atomic mass approximately 14.
Therefore, while the atomic mass generally increases with the atomic number, it's not a simple linear relationship. The presence of different isotopes and the varying number of neutrons they have make the relationship more complex.
