Final answer:
The deflection of alpha particles depends on their kinetic energy, as higher energy allows them to approach the gold nucleus more closely before Coulomb forces cause deflection. Greater energy leads to a smaller distance of closest approach and potentially larger scattering angles. This behavior played a crucial role in the development of the nuclear model of the atom.
Step-by-step explanation:
The amount of deflection of alpha particles is closely related to the energy of these particles. When Rutherford conducted his classic gold foil experiment at the beginning of the 20th century, he observed that alpha particles, which are high-energy doubly charged helium nuclei, were deflected by the gold nuclei at large angles. This deflection is caused by the Coulomb interaction between the positively charged alpha particles and the positively charged protons in the gold nucleus.
Alpha particles with higher energy can get closer to the gold nucleus before being deflected, because their higher kinetic energy allows them to overcome the electrostatic repulsion to a greater extent. However, once the electrostatic repulsive force becomes equal to the particle's kinetic energy, the alpha particle will come to a momentary stop and then be deflected. The distance at which this occurs is known as the distance of closest approach. The higher the energy of an alpha particle, the smaller this distance will be, leading to a greater potential for large-angle scattering, as demonstrated by the occasional alpha particles that Rutherford found bouncing back toward the source of emission.
The unexpected large deflections and even reversal of direction indicated that the atom's positive charge and bulk of mass were concentrated in a very small space, leading to the formulation of the nuclear model of the atom. This discovery also indicated that atoms consisted of mostly empty space, with dense, massive nuclei - a groundbreaking observation that altered our fundamental understanding of atomic structure.