LIFESCI 7A Chapter Notes - Chapter 2.1: Atomic Number, Unit, Atomic Mass
Document Summary
Section 2. 1 the atom is the fundamental unit of matter. Elements: pure substances that could not be broken down further by the methods of chemistry. 94 occurring naturally and 24 created artificially. Elements are often indicated by a chemical symbol that consists of a one- or two- letter abbreviation of the name of the element. Atom contains a dense central nucleus made up of protons and neutrons. Electrons move around the nucleus at some distance from it. Carbon has 6 protons, 6 neutrons, and 6 electrons. Each has a mass one 1 and electron has a negligible mass. Isotopes: same elements that have different numbers of neutrons. Atomic mass is sometimes indicated as a superscript to the left of the chemical symbol. Orbitals: where an electron is present most of the time. The maximum number of electrons in any orbital is two.
