AtomsAtoms are the building blocks of matter. Everything around us is made up of atoms. The atom is more than a million times smaller than the thickness of a human hair. The smallest speck visible under an ordinary microscope contains more than 10 billion atoms. Even though atoms are incredibly small, they are made up of even smaller particles: protons, neutrons, and electrons. These are called subatomic particles. Each element has a defined number of subatomic particles, which constitute the center of the atom, called the nucleus. The proton, a subatomic particle that carries a positive charge, is made up of 3 quarks. The proton is one of the few particles that are stable on their own. The positive charge of protons is 1.602 x 10^-27 coulombs. Protons have a mass of 1.67 x 10^-27 kg. Together with neutrons, they account for most of the mass of atoms. The number of protons in an atom's nucleus determines what type of element it is. The atomic number of an element is equal to the number of protons in the nucleus of each atom. Protons are influenced by all four fundamental forces that govern the interactions between particles and the energy of the universe. The electromagnetic force arises from matter carrying an electric charge. It causes the positively charged protons to attract the negatively charged electrons and keep them in orbit around the atom's nucleus. This force causes even closely packed protons in the atom's nucleus to repel each other. ...