How does the electron transport chain produce ATP? What is the driving force?

1. ETC transfers electrons from NADH and FADH2 to O2 through 4 complexes -Each complex increases in electron affinity 2. 2 Electron shuttles help move electrons between complexes 3. O2 High affinity takes electrons from the cytochrome 4. Causing a sequence where electrons from more electronegative molecules move to less electronegative ones -Drives the ETC