Atoms, Ions, and Molecules

We refer to methane gas, water, and sodium as substances. We can now characterize these substances into elements and compounds. Chemistry is the study of all of the “stuff” in the universe. In chemistry we refer to this “stuff” as matter. Recall, that matter is anything that has mass and occupies space. Flowers, trees, sand, water, methane gas, sodium, gold, people, DNA, air, are all examples of matter.

Matter can be classified into two separate groups. The first group are pure substances which consist of elements and compounds. An element is a pure substance that cannot be chemically broken down into simpler substances. Elements are composed of atoms. An atom is the smallest particle of an element that still retains all of the element’s characteristics. A compound is a pure substance that can be broken down chemically into simpler substances. The second group consists of mixtures of pure substances and may be considered an extension of the first group.

In this module, we will classify elements and their properties using the periodic table. In addition, the Law of Mass Conservation will be used to determine the mass of products formed in a chemical reaction. The Law of Multiple Proportions will be discussed. Thomson’s cathode-ray experiment, Millikan’s oil drop experiment, and Rutherford’s gold foil experiment will be explained in terms of how they contributed to modern atomic theory. The structure and size of atoms will be discussed and the number of atoms in a given sample will be calculated. Atomic mass will be calculated when give the fractional abundance (or percent abundance) and mass of each isotope. We will classify bonds as ionic or covalent and classify matter as a mixture or pure substance. Conversions between grams and numbers of moles or atoms using molar mass and Avogadro’s number will be shown. Finally, nomenclature will be presented.

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