Simple pictures showing orbital shapes are intended to describe the angular forms of regions in space where the electrons occupying the orbital are likely to be found. The diagrams cannot, however, show the entire region where an electron can be found, since according to quantum mechanics there is a non-zero probability of finding the electron anywhere in space. Instead the diagrams are approximate representations of boundary or contour surfaces where the probability density | ψ(r, θ, φ) |2 has a constant value, chosen so that there is a certain probability (for example 90%) of finding the electron within the contour. Although | ψ |2 as the square of an absolute value is everywhere non-negative, the sign of the wave function ψ(r, θ, φ) is often indicated in each subregion of the orbital picture.
[Cross-section of computed hydrogen atom orbital (ψ(r, θ, φ)2) for the 6s (n = 6, ℓ = 0, m = 0) orbital.]
I have a question here, if electrons can be found anywhere in the space with non-zero probability, can we give a definite boundary for the atom? i.e can we determine the radius of atom?
My sir has said me that, radius of atom is around $10^{-10}$m (from the $X$-ray experiments), but as we can have non-zero probability of finding the electron even beyond $10^{-10}$m, how can we say specific radius of an atom?