WebLecture: The Periodic Table
Kotz and Triechel, Chemistry and Chemical Reactivity Chapter 2: Section 5
2.5 The Periodic Table The periodic table is one of supreme accomplishments of information representation (I'd put the Hertzprung-Russell diagram of stellar characteristics in this category as well). This way of looking at chemical elements allows us to quickly identify a given element by its atomic mass, bonding characteristics, and relative reactivity with other elements. By reactivity, we mean the way that it reacts to form molecular compounds with other elements. By looking at the position of a given element in the periodic table, we can predict many of its characteristics and behaviors.
The evidence for atomic structure and periodic table relationships comes from several key experiments.
- The periodic table lays out the known elements in an array that helps explain their individual chemical characteristics and relationships to other elements. We move from top to bottom and left to right in increasing mass and atomic number. Later you will discover how the position of elements are related to their electron configurations and reactivity.
- The names and characteristics of the chemicals are your vocabulary for the year. Time invested now studying the periodic table will pay you. Understand the information given for each element. Note the color coding and the particular characteristics of each type of element (metal, non-metal, metalloids, noble gases).
- Go back and forth between the descriptions of the groups and the periodic table. Be able to give the general characteristics of each group. Understand what an allotrope is.
- John Dalton's experiments in the early 1800s showed that elements combined in whole-number ratios whether measured by mass or by volume, and that different ratios of the same elements had different properties: H2O (water) and H2O2 (peroxide) are distinct substances.
- J. J. Thomson's experiments with cathode ray tubes revealed that particles smaller than hydrogen, the smallest element, existed. Thomson's beta rays (later identified as electrons) proved the atom itself was divisible.
- The Curies' experiments with radiation not only showed again that atoms had smaller component particles, but that atoms could change from one element to another by losing or gaining components.
- Rutherford's experiments demonstrated that atoms were mostly space.
- Millikan's experiment allowed him to determine the charge-to-mass ratio on the electron.
Homework problems: Please visit the Moodle for the current assignment and posting instructions. Do all the homework problems assigned and check the forum for your posting assignment.
Lab: Read Illustrated Guide to Home Chemistry Experiments, "Chapter 5: Mastering Lab Skills".
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