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Chemistry LibreTexts

3: Chapter 3 - Atoms and Elemental Properties

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    • 3.1: Prelude to Atoms, Molecules, and Ions
      The angstrom unit is named after Anders Jonas Ångström, a nineteenth-century Swedish physicist. Ångström's research dealt with light being emitted by glowing objects, including the sun. Ångström studied the brightness of the different colors of light that the sun emitted and was able to deduce that the sun is composed of the same kinds of matter that are present on the earth. By extension, we now know that all matter throughout the universe is similar to the matter that exists on our own planet.
    • 3.2: Atomic Theory
      Chemistry is based on the modern atomic theory, which states that all matter is composed of atoms. Atoms themselves are composed of protons, neutrons, and electrons. Each element has its own atomic number, which is equal to the number of protons in its nucleus. Isotopes of an element contain different numbers of neutrons. Elements are represented by an atomic symbol. The periodic table is a chart that organizes all the elements.
    • 3.3: Masses of Atoms and Molecules
      The atomic mass unit (u) is a unit that describes the masses of individual atoms and molecules. The atomic mass is the weighted average of the masses of all isotopes of an element. The molecular mass is the sum of the masses of the atoms in a molecule.
    • 3.4: Organization of the Elements - The Periodic Table
    • 3.5: Ions and Ionic Compounds
      Ions form when atoms lose or gain electrons. Ionic compounds have positive ions and negative ions. Ionic formulas balance the total positive and negative charges. Ionic compounds have a simple system of naming. Groups of atoms can have an overall charge and make ionic compounds.