Question

What is the pattern that the atomic number and mass follow in the periodic table?

Answer 1

Generally, as the atomic number increases, the mass number increases. This is due to myriad factors.

A few are the magnitude of subatomic particles within the nucleus. Here's a graphical representation,

Generally the trend holds, however for a few atoms (e.g. `Ar`), heavier isotopes are more common. Hence, we have those little anomalies within the line.