The modern model of the atom describes electrons in a little less specific detail than earlier models did. Why is it that being less sure about the placement of electrons in an atom is actually an improvement over earlier models? The plum pudding model of the atom states that

It is because one cannot know exactly the position of the electron within the atom.

One formulation of Heisenberg's Uncertainty Principle tells us that one cannot know simultaneously  the position and momentum of the electron, so one cannot specify exactly either coordinate because the other would be infinite.

Bohr specified the most probable position of the electron at its lowest energy level in hydrogen and the product of the two would be about the Heisenberg value.