Heisenberg uncertainty: for an electron in atom (Δx ~ 10⁻¹⁰ m), minimum momentum uncertainty:

Δp ≥ ħ/(2 Δx) = 1.05 × 10⁻³⁴ / (2 × 10⁻¹⁰) ≈ 5.3 × 10⁻²⁵ kg m/s. Corresponds to velocity uncertainty ~5.8 × 10⁵ m/s — substantial, confirming that classical orbits make no sense at atomic scale.