Atomic Structure and the Periodic Table
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This document provides an overview of the history and development of atomic theory, including key discoveries and models. It describes early ideas from Democritus and Aristotle, foundations laid by laws of conservation of mass, definite proportions, and multiple proportions. Developments include Dalton's atomic theory, discovery of the electron, proton, neutron, isotopes, and the nuclear model of the atom. The periodic table is introduced along with atomic number, mass number, and calculating average atomic mass.
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Atomic Structure and the Periodic Table
- 1. Atomic Structure & the Periodic Table
- 8. Cathode Ray Tube High Voltage Cathode Ray (electrons) Metal disk (cathode) Metal disk (anode) Gas at very low pressure
- 9. Cathode Ray Tube High Voltage Cathode Ray (electrons) Metal disk (cathode) Metal disk (anode) Gas at very low pressure Negative plate Positive plate
- 12. Cathode Ray Tube High Voltage Cathode Ray (electrons) Metal disk (cathode) Metal disk (anode) Gas at very low pressure Negative plate Positive plate protons
- 21. #16 The element copper has naturally occurring isotopes with mass numbers of 63 and 65. The relative abundance and atomic masses are 69.2% for mass = 63.0 amu, and 30.8% for mass = 65.0 amu. Calculate the average atomic mass of copper.
- 24. Properties of Subatomic Particles Particles Symbol Charge Relative Mass Mass Electron e - 1- 1/1840 amu 9.11 x 10 -28 g Proton p + 1+ 1 amu 1.67 x 10 -24 g Neutron n º 0 1 amu 1.67 x 10 -24 g
Notes de l'éditeur
- Electrons were discovered by Thomson using a cathode ray tube in 1897. Thomson performed experiments that involved passing electric current through gases at low pressure. He sealed the gases in glass tubes fitted at both ends with metal disks called electrodes. The electrodes were connected to a source of high-voltage electricity. One electrode, the anode, became positively charged. The other electrode, the cathode, became negatively charged. The glowing beam formed between the electrodes. This beam, which traveled from the cathode to the anode, is called a cathode ray. Thomson found that cathode rays are attracted to metal plates that have a positive electrical charge. He determined the particle (electron) was negatively charged.
- A narrow beam of alpha particles (2 protons and 2 neutrons) was directed at a piece of gold foil. It was found that while most of the particles passed straight through, some bounced straight back or were deflected at angles. This experiment showed that most of the atom was empty space, but that atoms had a sold, positive core.
- If cathode rays are electrons given off by atoms, what remains of the atoms that has lost the electrons? First, atoms have no net electric charge; they are electrically neutral. Second, electric charges are carried by particles of matter. Third, electric charges always exist in whole-number multiples of a single basic unit; that is, there are no fractions of charges. Fourth, when a number of negatively charged particles combines with an equal number of positively charged particles, an electrically neutral particle is formed. Evidence for such a positively charged particle was found in 1886. when E. Goldstein observed a cathode-ray tube and found rays traveling in the direction opposite to that of the cathode rays. He called these rays canal rays and concluded that they were composed of positive particles called protons.
- Bothe & Chadwick were both members of Rutherford’s lab, therefore, he is sometimes credited with the discovery of the neutron.