An atom is normally electrically neutral .Why then should an alpha particle be deflected by the atom under any circumstances?
What if the alpha particle, which has a + charge, gets near the nucleus of the target atom? Then it is inside the electron shell of the target and feels mainly the repulsion force of the positively charged nucleus. Remember Gauss's law that it is only the charges inside (at a lower radius than) the shell you are at that cause an electric field where you are. That is for uniformly charged shells of course, but that is the idea.
and remember also that an atom is mostly empty space, so the nucleus is a powerful repulsive force.
An atom is considered electrically neutral because it has an equal number of positively charged protons in the nucleus and negatively charged electrons orbiting the nucleus. However, there are circumstances where an alpha particle can be deflected by an atom. This phenomenon can be explained by the concept of electric fields and the interaction between charged particles.
When an alpha particle approaches an atom, it experiences the electric field created by the positively charged nucleus of the atom. The alpha particle is itself positively charged since it consists of two protons and two neutrons, which gives it an overall charge of +2. So, when the positive alpha particle comes close to the positive nucleus, there is an electrostatic repulsion between them.
According to Coulomb's law, particles with the same charge repel each other, causing the alpha particle to be deflected or even completely deflected off its original path by the repulsive force between the alpha particle and the nucleus. This deflection depends on the energy and trajectory of the alpha particle, as well as the strength of the electric field experienced at that point.
Therefore, despite atoms being electrically neutral overall, the deflection of an alpha particle by an atom can occur due to the repulsive forces between charged particles.
The deflection of an alpha particle by an atom is due to the interaction of their electric charges. While an atom is normally electrically neutral, meaning it has an equal number of protons and electrons, the distribution of these charges is not perfectly symmetric.
Inside the atom, the protons are concentrated in the tiny nucleus at the center, while the negatively charged electrons orbit around it. This distribution creates an electric field, and when an alpha particle approaches the atom, it experiences this electric field, which can cause deflection.
To understand why an alpha particle would be deflected, we need to consider the electric force between charged particles. According to Coulomb's Law, this force is directly proportional to the product of the charges and inversely proportional to the square of the distance between them. Since the alpha particle is positively charged (consisting of two protons and two neutrons), and the atom has negatively charged electrons, there can be a repulsive force between them.
When the alpha particle comes close to the atom, the repulsive force between the positive charge of the alpha particle and the negative charge of the electrons can cause the alpha particle to be deflected or even change its direction. The extent of deflection depends on factors such as the relative mass and velocity of the alpha particle, as well as the distance of closest approach to the atom.
This phenomenon is known as the Rutherford scattering experiment, which played a crucial role in understanding the structure of the atom and confirming the existence of the atomic nucleus. It revealed that atoms are not a homogeneous, uniformly distributed mass but rather consist of a dense, positively charged nucleus surrounded by a cloud of electrons.