Presentation on theme: "Chapter 3.2. Objectives 1. Summarize the observed properties of cathode rays that led to the discovery of the electron. 2. Summarize the experiment carried."— Presentation transcript:
Objectives 1. Summarize the observed properties of cathode rays that led to the discovery of the electron. 2. Summarize the experiment carried out by Rutherford and his co-workers that led to the discovery of the nucleus. 3. List the properties of protons, neutrons, and electrons. 4. Define atom.
Structure of the Atom Define atom: smallest particle of an element that retains the chemical properties of that element. Nucleus very small region located at the center of an atom Contains 1.Protons – positive charged particle 2.Neutron – particle with NO charge Area surrounding nucleus Electron cloud 1.Electrons – negative charged particle Subatomic particles Visual Concept – Click Here
Properties of subatomic particles
Discovery of the Electron Late 1800’s – J.J. Thomson discovered the electron through experiments with cathode- ray tubes. Robert A. Millikan – 1909 – Oil drop experiment Electron is 1/1837 the mass of hydrogen atom Plum Pudding Model of atom Visual Concept 2 – Click Here Visual Concept 1 – Click Here
Discovery of the Atomic Nucleus In 1911 – Ernest Rutherford – Gold Foil Experiment Showed that there was a small – dense positively charged nucleus of an atom. Visual Concept – Click Here
Composition of the Atomic Nucleus Nuclear Forces – Short range proton-neutron, proton-proton, and neutron-neutron forces that hold the nuclear particles together Sizes of Atoms Nucleus compared to rest of atom - approximately size of marble compared to a large football stadium. Atom is mostly empty space All atomic nuclei are made of protons and neutrons. Atoms are electrically neutral - contain equal numbers of protons and electrons