Atomic Theory of MatterAtomic Theory of MatterAtomic Theory of MatterThe ElectronDiscovery of the NucleusSubatomic ParticlesSymbols of ElementsAtomic NumberMass NumberIsotopesAtomic MassPeriodic TableChapter 2 1Atomic Theory of MatterEach element is composed of extremely small particles called atoms.All atoms of a given element are identical to one another in mass and other properties, but the atoms of one element are different from the atoms of all other elements.Chapter 2 2Atomic Theory of MatterCompounds are formed when atoms of more than one element combine; a given compound always has the same relative number and kind of atoms.Chapter 2 3Atomic Theory of MatterAtoms of an element are not changed into atoms of a different element by chemical reactions; atoms are neither created nor destroyed in chemical reactions.The ElectronChapter 2 4Discovery of the NucleusChapter 2 5Subatomic ParticlesChapter 2 6Chapter 2 7Symbols of ElementsElements are symbolized by one or two letters.Chapter 2 8Atomic NumberAll atoms of the same element have the same number of protons: the atomic number (Z).Chapter 2 9Mass NumberThe mass number (A) is the total number of protons and neutrons in the atom.Chapter 2 10IsotopesIsotopes are atoms of the same element (they have the s ame number of protons) with different masses (they have diffe rent numbers of neutrons).Chapter 2 11Atomic MassThe atomic mass unit (amu) is defined as exactly one-twelfth the mass of a carbon-12 atom.Periodic TableChapter 2