Many theories about atomic structure have molded the current view of the atom. the quantum model suggests that electrons

behave as waves and the probability of finding the electron is determined by the factor, ψ²

Explanation:

Erwin Schrödinger proposed quantum mechanical model of atom in which electron behave as waves. He introduced ψ, which is the amplitude of the wave of the coordinates (x, y ,z ). ψ² represents probability of finding the electron in the given region above within the atom.

The atomic orbital is the region within the atom which encloses where electron is more than 90% probability.

the density(ratio between mass and volume as m/v) decreases from top to bottom in periodic table group as the size increases and nuclear charge decreases. but in periods density increases from left to right as atom size decreases and nuclear charge increases.