Alberta Grade 9 Science PAT Practice Test

Electrons are described by quantum mechanics as existing in orbitals—regions of space around the nucleus where there is a high probability of finding an electron. This creates an electron cloud rather than a precise path. You can’t know an exact location or path due to the uncertainty principle, so the modern view talks about where the electron is most likely to be found, not a fixed orbit. The cloud isn’t spread uniformly; the density of the cloud depends on the specific orbital (shape and energy), giving rise to various forms like spherical s-orbitals or dumbbell-shaped p-orbitals. The idea of electrons circling in fixed orbits is from an older model, and electrons aren’t simply inside the nucleus or evenly distributed outside it.