In our previous discussion of water, we learned about the characteristics of water as the universal solvent and literally how it dissolves many substances. One super critical concept is that of polarity. Polar substances dissolve in polar substances. And non-polar substances do not, which means that most water pollutants have some degree of polarity. Water is often called the universal solvent. The precipitation from the clouds in the hydrological cycle allowed fresh water to dissolve the minerals in the earth, leading to the emergence of salty oceans. Syvalion formation and hydrogen bonding are critical to these processes. Ions are formed when an atom loses electrons or gains electrons. In a formula of an ion, it compound the number of positive charges equal the number of negative charges. Most atoms have only one stable ion has seen in group one and group two metals or to halogens. Transition metals can form more than one stable ion. Anionic compound like sodium chloride known as table salt has an ionic bond forming a very strong attractive force between the sodium ion and the chloride ion. Negative ions are called anions and are usually non-metals. So to name the ionic compound, we use the name of the metal plus the name of the anion. Sodium ion plus the chloride ion will be sodium chloride. Naming polyatomic ions is also easy. Name the cation, the metal or positive ion first, and then name the anion. NASO4 is sodium sulfate. Sodium is the cation and the sulfate is the anion. Ions dissolved in water are said to be hydrated, that is surrounded by water molecules. When salts dissolve in water to form aqueous solutions, they are forming ions and solutions. These ions can conduct electricity. Electricity is the movement of electrons. Different salts have different psiability and water depending on the strength of their ionic bond. However, group 1 metal ions are generally soluble as our nitrates, chlorides, and sulfates. Group 2 metals are less soluble, so carbonates, hydroxides, and sulfates are poorly soluble or unsoluble in pure water. Hydrogen bonding leads to increased psiability and water. For example, when table sugar, a sucrose molecule is dissolved in water. It interacts with and becomes surrounded by water molecules. The sucrose molecules do not dissociate like ion compounds do. Covalent molecules remain intact when dissolved in water but form hydrogen bonds with the water molecules. The Clean Water Act regulates the amount of toxic ions that can be in drinking water. It also regulates other compounds like benzene. Some ions or compounds are toxic enough that the EPA has set a goal of zero, such as lead. Since the early 1970s, we have been trying to be better stewards of the earth's water. Because sewerages, the leading polluter of water and cities produce large amounts of sewerage, water treatment systems have been developed. The different stages are generally characterized as primary, secondary, and tertiary treatment. Fair banks recently stopped adding fluoride to water. What do you think of that? A primary system uses precipitation to produce sludge that is deposited in landfills. Secondary systems break down molecules and kill harmful microbes. Tertiary systems remove other organic compounds and some ions. Have you ever considered where to medicine, you take up, winds up? Access to Clean Water varies around the world. In many places where there is conflict, there is also poverty and a spoiled environment. Healthy social systems depend on healthy ecosystems, which depend on Clean Water. Important alternatives for purifying water are ion exchangers, revales, asmosis, and distillation. Asmosis uses a semi-permeal membrane that allows the solvent water to be exchanged between two compartments while blocking the exchange of the soluble water. Biological membranes work this way as to carefully design artificial membranes. The purification of water by distillation on a small scale is essentially the same process seen in hydrological cycle.