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Chemistry LibreTexts

3: Atoms and the Periodic Table

[ "article:topic-guide", "authorname:gordone", "showtoc:no" ]
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    • 3.1: Basic Atomic Theory
      All modern scientists accept the concept of the atom, but when the concept of the atom was first proposed about 2,500 years ago, ancient philosophers laughed at the idea. It has always been difficult to convince people of the existence of things that are too small to see. We will spend some time considering the evidence (observations) that convinced scientists of the existence of atoms.
    • 3.2: Development of the Modern Periodic Table
      The periodic table is an arrangement of the elements in order of increasing atomic number. The periodic table is one of the cornerstones of chemistry because it organizes all the known elements on the basis of their chemical properties. Elements that exhibit similar chemistry appear in vertical columns called groups (numbered 1–18 from left to right); the seven horizontal rows are called periods.
    • 3.3: Subatomic Particles - Electrons, Protons, and Neutrons
      Now that we know how atoms are generally constructed, what do atoms of any particular element look like? What types of particles are contained inside an atom? In this section, we will explore the three subatomic particles most atoms contain.  Experiments in the late 19th and early 20th centuries helped to define and locate each of these three atomic pieces.  Overviews of these experiments will help you to appreciate the efforts involved to explain the structure of the atom.
    • 3.4: Atomic Mass and Atomic Number
      Atoms are the fundamental building blocks of all matter and are composed of protons, neutrons, and electrons. Because atoms are electrically neutral, the number of positively charged protons must be equal to the number of negatively charged electrons. Since neutrons do not affect the charge, the number of neutrons is not dependent on the number of protons and will vary even among atoms of the same element.
    • 3.5: Isotopes
      Isotopes are atoms of the same element that differ in the amount of neutrons and atomic mass. Almost all elements on the periodic table have at least two different natural isotopes. Many elements have synthetic isotopic forms that have been made by nuclear chemists and/or physicists. Chemically, isotopes appear to be the same. For example, the two most abundant forms of uranium look physically the same and react to other materials in a similar manner.
    • 3.6: The Importance of Ions to a Chemist
      Chemists appreciate isotopes and use them in basic and applied research. However, they are more concerned with the movement of electrons. When an atom gains or loses electrons, it becomes a charged species or an ion. When this occurs, the nucleus is not altered. For atoms that lose electrons, an overall positive charge will result (#protons > #electrons). Atoms that form these types of ions are called cations.
    • 3.E: Atoms and the Periodic Table (Exercises)
      These are homework exercises to accompany Chapter 3 of the Furman University's LibreText for CHE 101 - Chemistry and Global Awareness.