Schrodinger equation: Hpsi = Epsi (time-independent form). Solutions give wave functions psi(r,theta,phi) = R(r) x Y(theta,phi). |psi|^2 gives probability density. Orbital = region of space where probability of finding electron is high (typically 90-95%). Radial distribution function: P(r) = 4pi$r^2$*$R^2$(r). Shows probability of finding electron at distance r. Maximum of P(r) for 1s occurs at r = $a_0$ (Bohr radius). This is the most probable distance, NOT the average distance. For multi-electron atoms, orbitals have the same shapes but different energies (degenerate orbitals split due to electron-electron repulsion and shielding). Effective nuclear charge $Z_{eff}$ = Z - sigma (Slater's rules).