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# Chapter Summary Atoms are tiny particles that make up all matter. The smallest part of an element is the atom. Atoms contain three sub-atomic particles. * **Protons:** Have a mass of 1 a.m.u., a charge of +1, and are found in the nucleus. * **Neutrons:** Have a mass of 1 a.m.u., have no charge,...

# Chapter Summary Atoms are tiny particles that make up all matter. The smallest part of an element is the atom. Atoms contain three sub-atomic particles. * **Protons:** Have a mass of 1 a.m.u., a charge of +1, and are found in the nucleus. * **Neutrons:** Have a mass of 1 a.m.u., have no charge, and are found in the nucleus. * **Electrons:** Have a mass of $\frac{1}{1836}$ a.m.u., have a charge of -1, and are located in the electron cloud surrounding the nucleus. Atoms of the same element have the same number of protons in the nucleus. Ions are charged atoms that have lost or gained electrons. Isotopes are atoms of the same element with a different number of neutrons in the nucleus. The Bohr model places electrons on energy levels. The first energy level can hold two electrons, and the next two energy levels can hold eight electrons each.