Albert Einstein had many notable discoveries, but he did not split the atom. The atom was split by Ernest Rutherford, a physicist from New Zealand, in 1919.
Some of Einstein's notable contributions to science include The Theory of Relativity, The Special Theory of Relativity, and a paper on mass-energy equivalence. His mass-energy equivalence paper resulted in his famous E=mc^2 formula. Einstein made many contributions to science and physics, but he also admired Rutherford. Einstein is said to have felt Rutherford was “a second Newton." In addition to splitting the atom, Rutherford also discovered elements can change their structure and created the nuclear model of an atom.