![]() ![]() Its atomic number is 92 and its atomic mass is 238 (92 + 146). The most common isotope of uranium has 92 protons and 146 neutrons. Its atomic number is 14 and its atomic mass is 28. For example, silicon has 14 protons and 14 neutrons. For most of the remaining elements, there are more neutrons than protons, because extra neutrons are needed to keep the nucleus together by overcoming the mutual repulsion of the increasing numbers of protons concentrated in a very small space. For helium, it is 4: two protons and two neutrons.įor most of the 16 lightest elements (up to oxygen) the number of neutrons is equal to the number of protons. For hydrogen, the atomic mass is 1 because there is one proton and no neutrons. The number of protons is the atomic number, and the number of protons plus neutrons is the atomic mass. ![]() The positively charged protons tend to repel each other, and the neutrons help to hold the nucleus together. All other elements have neutrons as well as protons in their nucleus, such as helium, which is depicted in Figure 2.2. The proton forms the nucleus, while the electron orbits around it. The element hydrogen has the simplest atoms, each with just one proton and one electron. Table 2.1 Charges and masses of the particles within atoms Elementary Particle Both protons and neutrons have a mass of 1, while electrons have almost no mass. The negative charge of one electron balances the positive charge of one proton. As summarized in Table 2.1, protons are positively charged, neutrons are uncharged and electrons are negatively charged. ![]() 2.1 Electrons, Protons, Neutrons, and AtomsĪll matter, including mineral crystals, is made up of atoms, and all atoms are made up of three main particles: protons, neutrons, and electrons. ![]()
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