Atoms were supposed to be indivisible, but in 1897 J.J. Thompson (1856-1940), a British physicist, found the electron, a negatively charged particle about 1/1800 the size of the nuclear particles. He then designed what was called a "plum pudding" model of how the atom was shaped that did not convince many.
In 1913, Niels Bohr (1885-1962), a Danish Physicist and then student of Rutherford, laid down a model of the atom based on quantum theory that significantly improved Rutherford's model. He suggested that electrons were confined to clearly defined, quantized orbits around the nucleus. An electron must emit or absorb a quanta to move between these orbits. When the light from a heated object was passed through a prism, it produced a multi colored spectrum. The appearance of fixed lines in this spectrum was successfully explained by these orbital transitions.
Gilbert Newton Lewis (1875-1946), an American chemist, then in 1916 claimed that chemical bonding between atoms involves the electrons in the orbitals. Bonding electrons were shared by the atoms.
In 1932, Linus Pauling (1901-1994), an American chemist, published a landmark paper where laid down his theory of orbital hybridization and analyzed the tetravalency of carbon. That year he also established the concept of electronegativity, and imbalance in the electron cloud that give rise to a partial charge, and developed a scale that would help predict the nature of chemical bonding. Electrons were by then known to circle around the nucleus in particular fashions called orbitals, they thus had forms where they spent most of their time, that explained the nature of bonding when considered.
Sir James Chadwick (1891-1974) found the neutron, the uncharged second main particle in the nucleus, also in 1932. Nuclear physics was now well on the way to the atom bomb.
However, what has become very important in medicine is to be able to visualize how molecules look in space and how they potentially interact. As I earlier mentioned, such knowledge can be used in the production of new antibiotics from knowing the structure of the ribosome to design drugs, new antibiotics, that bind non-covalently, ie, not via chemical reactions. Also other potentially new drugs that can bind to various receptors on cells, that when bound can give desired effects, can be designed in this fashion.
Data from Wikipedia