All atoms of the same element are identical in mass and other properties.During a chemical reaction, atoms are rearranged, but they do not break apart, nor are they created or destroyed Atoms cannot be broken into smaller pieces.Matter is made up of tiny particles called atoms.It is for this reason that Democritus’ ideas on atoms were dismissed until 1808, when John Dalton, an English scientist, proposed four fundamental assumptions based upon observations that we call Dalton’s Atomic Theory. Philosophers, like Democritus, based most of their ideas off of thought experiments like the one above instead of actual observations and experimentation. He proposed that the smallest piece that any element (like aluminum) can be divided into and still be recognized as that element is an Atom, a word derived from the Greek word atomos, meaning “indivisible”. However, one brilliant philosopher, Democritus, argued that there is a limit. Most, like Aristotle, argued that matter could be divided infinitely. How long could you continue cutting, assuming that you had no limitations based on your own abilities? Is there a limit on how small matter can be broken up into, or could you infinitely divide matter into smaller and smaller pieces? This argument dates as far back as the Greek philosophers. Like the ancient Greeks we can perform a simple thought experiment that raises a very important question for modern chemistry: suppose you were given a piece of aluminum foil and asked to cut the foil in half over and over. What are the smallest building blocks of everyday objects? This is a question that has interested man since the age of the Greek philosophers. 2.1 Atomic Theory with Historical Perspectives 2.2 Introduction to Elements and the Periodic Table 2.3 Dmitri Mendeleev and the development of the periodic table 2.4 Families of the Periodic Table 2.5 Defining the Atom Basic Atomic Structure – electrons, neutrons, and protons 2.6 Atomic Number – Protons Determine the Identity of an Element 2.7 Atomic Mass, Isotopes, and Allotropes 2.8 Electronic Structure of Atoms The Four Electronic Quantum Numbers Electron Orbital Filling Rules Electron Configurations and the Periodic Table Electron Configuration Solitaire Electron Configuration Shorthand Electron-Dot Symbols 2.9 Periodic Table Trends Atomic Size Electronegativity Ionization Energy Metallic and Nonmetallic Character 2.10 Chapter Summary and Homework 2.11 ReferencesĢ.1 Atomic Theory with Historical Perspectives This text is published under creative commons licensing, for referencing and adaptation, please click here. This content can also be downloaded as an printable PDF, adobe reader is required for full functionality.
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