The word 'atom' comes from the Greek for indestructible because the physicists and philosophers who first contemplated the existence of atoms believed they were indeed indestructible. We now know quite well that atoms can be destroyed, and ever since that was first accomplished, researchers have been trying to destroy them in more interesting ways to determine what indestructible pieces make up atoms. According to the Standard Model of particle physics there are only 12 fermions or matter particles, and researchers at the Karlsruhe Institute of Technology have recently reported that there can be no more.
These 12 particles have been divided into three generations of four each, according to the particles' similar properties. The first generation contains the electron, the electron neutrino, and the up and down quarks, with the latter two being the particles that construct all protons and neutrons. The other two generations are less common in nature and generally heavier particles, which is how the researchers have concluded there are no more generations. The Higgs boson, strongly believed to have been discovered at CERN recently, is what gives all particles their mass. To find it the researchers had to predict its properties based on the 12 particles of the Standard Model. If there were any additional, undiscovered particles though, the predictions would be off, and it could not have been found where it was.
By analyzing the data from numerous experiments from different particles accelerators, the researchers are 99.99999% certain their research is correct, though there is still more research to be done. The Higgs boson, if indeed it was the particle discovered recently, still has many secrets from us and those secrets may answer other important questions such as why matter dominated antimatter in after the Big Bang.