By Peter S. Cartwright, PE, CWS-VI
An understanding of water treatment requires a fundamental knowledge of chemistry. After all, water treatment is simply the removal, manipulation or conversion of chemical contaminants in water.
Each person has different needs when it comes to learning new and perhaps alien concepts; some require the material to be presented many times, some are fine with simply reading it, others work better in a lecture environment. Others learn better in with several formats.
It is also effective to receive education from different instructors, each with their own style. Tanya Lubner, PhD, presents an excellent fundamentals course at the annual WQA Educational Conference. WQA’s ‘Water Treatment Fundamentals’, edited by Joe Harrison, also provides valuable education in the basics.
The point is that someone who really wants to understand seemingly ‘impossible’ water chemistry has a multitude of resources readily available.
This monthly column is based on a water chemistry course developed for the Canadian Water Quality Association with the help of Kevin Wong, Executive Director. It will present a snippet of basic chemistry fundamentals every month, with the hope that ‘a little at a time’ will prove helpful.
This is not intended to be a comprehensive chemistry course, but rather basic instruction on chemistry as it relates to water and water treatment. It is hoped that your interest will be piqued and induce you to want to learn more.
The desired outcome is that it will help you become a more effective and valuable water treatment professional. Please get back to us with any questions or concerns; we welcome your input!
The Periodic Table
This month’s column focuses on the Periodic Table, with future columns to address: atoms, elements, molecules and compounds; chemical bonds; ions; acids, bases and salts; pH; chemical reactions; water analysis data; and a glossary of terms.
The Periodic Table of elements (shown below) is a list of every chemical element on this earth. It is not ‘cast in concrete’ as new elements are occasionally discovered (usually in conjunction with a radioactive reaction) and added. Each element has its own box containing valuable information: the number in the upper left hand corner is its atomic number, which is the number of protons or electrons.
The number at the bottom is its atomic weight (mass), which is the total number of protons plus the number of neutrons. The numbers on the upper right are the number of electrons in each orbital shell.
All elements look like tiny solar systems, with electrons (minus charge) orbiting around the nucleus in shells (usually several) containing a specific and predictable number of electrons. The nucleus contains protons (plus charge) and neutrons (no charge). All of these particles are extremely small, measured in terms of angstroms.
An angstrom (A) is 0.0001µ, or 0.1 nanometer. The diameter of a water molecule is approximately 3.2 A. (THE ANGSTROM SYMBOL IS “A” WITH ° ABOVE IT)
Reading the table
The relative locations of these elements in the Periodic Table is important. Note that reading left to right, the atomic number increases.
It is important for water professionals to understand valence and orbital information. This will become apparent as we move through this course.
Valence, in the vertical columns, designates the elements on the periodic table that share a common theme. Each column denotes the amount of electrons the element has in its outermost orbital (shell), or how many electrons it can easily share with another element to make compounds.
Electrons in the outermost shell (bottom numbers in the list) are generally shared with another element to form compounds. As an example, sodium (Na) has one electron to share and chlorine (Cl) has seven. So chlorine will easily accept one electron, as it naturally seeks eight electrons to be in its orbit.
The horizontal rows of elements in the Periodic Table show how many electron shells are associated with each element. Since sodium (Na) has one and chlorine has seven sharing the same row and, because both can hold eight electrons in that shell (to be the most stable), they naturally form a compound, NaCl.