Why can scientists ignore the gravitational force when studying the physics of an atom?

Scientists can ignore the gravitational force because the electrical force between protons and electrons in the atom is millions of times stronger than the gravitational force between the protons and electrons. The gravitational force is insignificant for masses as small as the proton and electron.

Scientists assume the gravitational force as negligible as compared to other forces present in the an atom because its value would be very small. Gravitational force is directly proportional to the mass of an object so small mass would lead to small force as well which is true for an atom. As compared to the nuclear forces, it would have a very small value.