Note: when a metal atom can form more than one positive ion, the charge on the ion is given by Roman Numerals in brackets. The negative ions of non-metals lose the ending of the atom's name and replace it with the letters -ide.
Polyatomic ions containing oxygen end in -ite and -ate. Polyatomic ions Molecules can also form ions, usually by gaining electrons and forming negative ions. Electrically charged molecules are known as polyatomic ions, literally "many atomed ions".
Although larger than most monatomic ions those composed of only one ion , polyatomic ions behave in the same way as other ions in forming salts with positive ions. Salts Salts are formed when positive and negative ions come together in giant ionic crystal lattices in ratios that give the overall crystal a zero charge. In other words, the total charge of all the positive ions equals the total charge of the negative ions. See the topic Making salts - the rules of electrovalency for more information on how salts form crystals and Ionic crystals - salts for the properties of giant ionic crystals.
Ions and salts Ions Polyatomic ions Salts. In acid-base chemistry, a salt is defined as the ionic compound that results from a neutralization reaction between an acid and a base. As such, salts are composed of cations positively charged ions and anions negative ions , and in their unsolvated, solid forms, they are electrically neutral without a net charge. There are several varieties of salts, and in this section we will consider basic salts. What makes a basic salt basic?
It is due to the fact that the anion in the salt is the conjugate base of a weak acid. For a generalized anion B — , the net ionic reaction is:. An example of a basic salt is sodium bicarbonate, NaHCO 3. The bicarbonate ion is the conjugate base of carbonic acid, a weak acid. Therefore, it reacts with water in the following fashion:. Because it is capable of deprotonating water and yielding a basic solution, sodium bicarbonate is a basic salt. Notice that for all of these examples, the anion is the conjugate base of a weak acid carbonic acid, bisulfate second dissociation step of sulfuric acid , acetic acid, hydrocyanic acid, hydrogen sulfide.
Keep in mind that a salt will only be basic if it contains the conjugate base of a weak acid. Sodium chloride, for instance, contains chloride Cl — , which is the conjugate base of HCl. Sodium Bicarbonate : Because the bicarbonate ion is the conjugate base of carbonic acid, a weak acid, sodium bicarbonate will yield a basic solution in water. When dissolved in water, acidic salts will yield solutions with pH less than 7. This is due either to the presence of a metal cation that acts as a Lewis acid which will be discussed in a later concept , or, quite commonly, due to a hydrolyzable proton in the cation or the anion.
Salts with acidic protons in the cation are most commonly ammonium salts, or organic compounds that contain a protonated amine group. Examples include:. An example of an acid salt is one containing any of these cations with a neutral base, such as ammonium chloride NH 4 Cl. Solid salt is formed when the water evaporates and the negatively charged chlorine ions combine with the positively charged sodium ions.
Solid sodium chloride exists in the form of tiny, cube-shaped particles called crystals. These crystals are colorless, have a density of 2. They also dissolve in water, separating into the component sodium and chlorine ions. This process known as ionization is important to many industrial chemical reactions. Common salt sodium chloride is found throughout nature.
It is dissolved in the oceans with an average concentration of 2. On land, thick salt deposits, formed by the evaporation of prehistoric oceans, are widely distributed. These deposits are true sedimentary rocks and are referred to as rock salt or halite. People obtain salt from the environment in many different ways.
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