Answer:
Ionic compounds are formed when positive and negative ions share electrons and form ionic bonds. The strong attraction between positive and negative ions often produces crystalline solids with high melting points. When there is a large difference in electronegativity between ions, ionic bonds are formed rather than covalent bonds. Cations, called cations, are listed first in the ionic compound formula, followed by negative ions, called anions.
Stable ionic compounds are electrically neutral in which electrons are shared between cations and anions to complete the outer electron shell or octant. When the positive and negative charges on the ions are the same or "cancel each other", you know you have the right formula for the ionic compound. Here are the steps to write and balance the formula: Identify the cation (the positively charged part). It is the weakest (most positively charged) ion. Cations include metals, which are usually on the left side of the periodic table. Identify anions (negatively charged moieties). It is the most negatively charged ion. Anions include halogens and nonmetals. Remember that hydrogen can carry a positive or negative charge in any way. Write the cation first, then the anion. Adjust the subscripts of the cations and anions so that the net charge is 0. Use the smallest integer ratio between the cations and anions to write the formula to balance the charges. If the cations and anions are of equal charge (eg +1/-1, +2/-2, +3/-3), then combine the cations and anions in a 1:1 ratio. An example is potassium chloride KCl. Potassium (K+) has a 1-charge, while chlorine (Cl-) has a 1-charge. Note that you don't write a subscript of 1. If the charges of the cation and anion are not equal, add subscripts to the ions as needed to balance the charges. The total charge of each ion is the subscript times the charge. Adjusted subscripts to balance charges. An example is sodium carbonate Na 2 CO 3 . The sodium ion has a +1 charge, multiplied by the subscript 2 gives a total charge of 2+. The carbonate anion (CO 3 -2 ) has a 2-charge, so there is no additional subscript. If you need to add a subscript to a polyatomic ion, enclose it in parentheses to clearly apply the subscript to the entire ion rather than individual atoms. An example is aluminum sulfate, Al 2 (SO 4 ) 3 . The parentheses surrounding the sulfate anion indicate that three 2-sulfate ions are required to balance 2 of the 3 charged aluminum cations.
Examples of ionic compounds
Many familiar chemicals are ionic compounds. A metal bonded to a non-metal is the death giveaway of an ionic compound you are dealing with. Examples include salts such as table salt (sodium chloride or NaCl) and copper sulfate (CuSO4).
