What is it that keeps elements on the periodic table different from one another?

The elements have different number of protons in their atoms. This keeps elements on the periodic table different from one another.

Number of protons is different

They all have different weights (compared to carbon12) also their properties often keep them different too with noticeable similarities due to their state (solid, liquid gas) triple science is paying off lol

Protons.

Atomic number.