The Basics of Water Chemistry: Elements, Atoms and Molecules
By Peter S. Cartwright, PE, CWS-VI
The basic chemistry fundamentals presented every month 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 simplest substances that contain the same type of atoms are called an element. Elements have unique physical and chemical properties.
At this time, more than 120 elements have been identified. The Periodic Table (see July, 2009 issue of WC&P) lists 118. The recent discoveries are elements that exist for nanoseconds before breaking down.
Understanding the Periodic Table is a matter of knowing the importance and the labels of the listed numbers. The atomic number is the number of protons in an atom, while the atomic weight is the number of protons plus the number of neutrons in an atomic element. The electron mass is negligible (Graphic 1).
The smallest part of an element that can exist is an atom (Graphic 2). The nucleus or center of the atom contains protons, which have a positive charge, as well as neutrons, which have no charge. Protons and neutrons both have a mass.
The orbit around the nucleus contains the electrons, which are equal to the protons and negative. These electrons are very small and their mass is considered negligible, weighing 2,000 times less than a proton or neutron (Graphic 3).
Hydrogen is a key to creating a molecule of water (Graphic 4). Two or more atoms in a definite arrangement and held together by chemical bonds are defined as a molecule.
The number of neutrons in a specific element can vary on rare occasions. Such an element is then classified as an isotope.
The second smallest element is helium (Atomic number 2), with two protons, two neutrons and two electrons (Graphic 5). Carbon, a bit larger element (Atomic number 6), has six protons, six neutrons and six electrons. It also has two orbital shells. (Graphic 6).
Nitrogen (Atomic number 7) and oxygen (Atomic number 8) are additional examples of elements that have two orbital shells (Graphic 7). Sodium, magnesium and chlorine have three orbital shells (Graphic 8).
These orbital shells determine the stability of an element and its ability to combine with other elements to form compounds. The maximum number of electrons in an orbit is two times the square of the number of orbit shells, one through 5 (Graphic 9).
About the author
Peter S. Cartwright, CWS-VI, President of Cartwright Consulting Company, of Minneapolis is a registered Professional Engineer in Minnesota. He has been in the water treatment industry since 1974,has authored over 125 articles, presented over 125 lectures in conferences around the world and has been awarded three patents. Cartwright has chaired several WQA committees and task forces and has received the organization’s Award of Merit. A member of WC&P Technical Review Committee since 1996, his expertise includes such high-technology separation processes as RO, UF, MF, UF electrodialysis, deionization, carbon adsorption, ozonation and distillation. Cartwright is also Technical Consultant to the Canadian Water Quality Association. He can be reached by phone (952) 854-4911; fax (952)854-6964; email firstname.lastname@example.org or on his website, www.cartwright-consulting.com.