What, if there is some, is the change in motion of electrons in the atoms of the medium when it reflects or refracts an electromagnetic wave?

Dear student,

To understand electromagnetic waves, one must first understand electric and magnetic fields and how they interact. Electric fields make electric charges attract or repel each other. Similarly magnetic fields cause magnetic forces.

There are two basic types of electric charges. They are positive and negative. In atoms, protons have positive charges and electrons have negative charges. Electric forces between the protons and electrons cause the electrons to orbit the nucleus. Like charges, such as two protons or two electrons, repel each other. Unlike charges, such as a proton and an electron, attract each other. These attractive or repulsive electric forces are governed by Coulomb's Law.

The protons and electrons are not actually in contact, so how can they exert forces on each other? We can't push or pull something without actually touching it, so why should electric charges be able to? The answer is electric fields. Any electric charge creates an electric field. An electric field exerts a force on another electric charge. Electric charges exert forces on each other via electric fields.