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Chemistry LibreTexts

1.3: Molecules and Compounds (IntroChem Tro)

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    239851
  • 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.

    • 1.3.1: 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.
    • 1.3.2: 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.
    • 1.3.3: Chemical Formulas- How to Represent Compounds
      A chemical formula is an expression that shows the elements in a compound and the relative proportions of those elements. A molecular formula is a chemical formula of a molecular compound that shows the kinds and numbers of atoms present in a molecule of the compound. An empirical formula is a formula that shows the elements in a compound in their lowest whole-number ratio.
    • 1.3.4: 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.
    • 1.3.5: 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.

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