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Chemistry LibreTexts

6: Molecules and Compounds

  • Page ID
    212479
  • There are many substances that exist as two or more atoms connected together so strongly that they behave as a single particle. These multiatom combinations are called moleculesThe smallest part of a substance that has the physical and chemical properties of that substance.. A molecule is the smallest part of a substance that has the physical and chemical properties of that substance. In some respects, a molecule is similar to an atom. A molecule, however, is composed of more than one atom.

    • 6.1: Prelude to Chemical Bonds
      Diamond is the hardest natural material known on Earth. Yet diamond is just pure carbon. What is special about this element that makes diamond so hard? Bonds. Chemical bonds.
    • 6.2: Sugar and Salt
      Both salt and sugar have radically different properties (both physical and chemical) than the constituent elements that make up these compounds. That is a central feature of chemical reactions as this chapter will discuss.
    • 6.3: Compounds Display Constant Composition
      A compound is a substance that contains two or more elements chemically combined in a fixed proportion. The elements carbon and hydrogen combine to form many different compounds. One of the simplest is called methane, in which there are always four times as many hydrogen particles as carbon particles. Methane is a pure substance because it always has the same composition. However, it is not an element because it can be broken down into simpler substances - carbon and hydrogen.
    • 6.4: A Molecular View of Elements and Compounds
      Most elements exist with individual atoms as their basic unit. It is assumed that there is only one atom in a formula if there is no numerical subscript on the right side of an element’s symbol. There are many substances that exist as two or more atoms connected together so strongly that they behave as a single particle. These multi-atom combinations are called molecules. The smallest part of a substance that has the physical and chemical properties of that substance.
    • 6.5: Lewis Electron Dot Diagrams
      Lewis electron dot diagrams use dots to represent valence electrons around an atomic symbol. Lewis electron dot diagrams for ions have less (for cations) or more (for anions) dots than the corresponding atom.
    • 6.6: Electron Transfer - Ionic Bonds
      The tendency to form species that have eight electrons in the valence shell is called the octet rule. The attraction of oppositely charged ions caused by electron transfer is called an ionic bond. The strength of ionic bonding depends on the magnitude of the charges and the sizes of the ions.
    • 6.7: Writing Formulas for Ionic Compounds
      Formulas for ionic compounds contain the symbols and number of each atom present in a compound in the lowest whole number ratio.
    • 6.8: Naming Ionic Compounds
      Ionic compounds are named by stating the cation first, followed by the anion. Positive and negative charges must balance. Some anions have multiple forms and are named accordingly with the use of roman numerals in parenthes. Ternary compounds are composed of three or more elements.
    • 6.9: Covalent Bonds
      Covalent bonds are formed when atoms share electrons. Lewis electron dot diagrams can be drawn to illustrate covalent bond formation. Double bonds or triple bonds between atoms may be necessary to properly illustrate the bonding in some molecules.
    • 6.10: Naming Molecular Compounds
      Molecular compounds are inorganic compounds that take the form of discrete molecules. Examples include such familiar substances as water and carbon dioxide. These compounds are very different from ionic compounds like sodium chloride. Ionic compounds are formed when metal atoms lose one or more of their electrons to nonmetal atoms. The resulting cations and anions are electrostatically attracted to each other.
    • 6.11: Other Aspects of Covalent Bonds
      Covalent bonds can be nonpolar or polar, depending on the electronegativities of the atoms involved. Covalent bonds can be broken if energy is added to a molecule. The formation of covalent bonds is accompanied by energy given off. Covalent bond energies can be used to estimate the enthalpy changes of chemical reactions.
    • 6.12: Molecular Shapes
      The approximate shape of a molecule can be predicted from the number of electron groups and the number of surrounding atoms.
    • 6.13: Nomenclature Summary
      Brief overview of chemical nomenclature.

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