Tham khảo sách 'chemistry part 4, julia burdge,2e (2009)', khoa học tự nhiên, hoá học phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 58 CHAPTER 2 Atoms Molecules and Ions Loses an electron Figure An electron is transferred from the sodium atom to the chlorine atom giving a sodium ion and a chloride ion. The oppositely charged ions are attracted to each other and form a solid lattice. Sodium atom Na Chlorine atom CI Gains an electron charge on the anion and a subscript for the anion that is numerically equal to the charge on the cation. If the charges are numerically equal then no subscripts are necessary. Let us consider some examples. Potassium Bromide The potassium ion K and the bromide ion Br- combine to form the ionic compound potassium bromide. The sum of the charges is 1 1 0 so no subscripts are necessary. The formula is KBr. Zinc Iodide The zinc ion Zn2 and the iodide ion I- combine to form zinc iodide. The sum of the charges of one Zn2 ion and one I- ion is 2 1 1. To make the charges add up to zero we multiply the 1 charge of the anion by 2 and add the subscript 2 to the symbol for iodine. Thus the formula for zinc iodide is Znl2. Ammonium Chloride The cation is NHj and the anion is CL. The sum of the charges is 1 1 0 so the ions combine in a 1 1 ratio and the resulting formula is NH4C1. Aluminum Oxide The cation is Al3 and the anion is O . The following diagram can be used to determine the subscripts for this compound The sum of the charges for aluminum oxide is 2 3 3 2 0. Thus the formula is A12O3. Calcium Phosphate The cation is Ca2 and the anion is PO4-. The following diagram can be used to determine the subscripts Caâ PO4 à The sum of the charges is 3 2 2 3 0. Thus the formula for calcium phosphate is Ca3 PO4 2. When we add a subscript to a polyatomic ion we must first put parentheses around the ion s formula to indicate that the subscript applies to all the atoms in the polyatomic ion. Naming Ionic Compounds An ionic compound is named using the name of the cation followed by the name of the anion eliminating the word ion from each. Several examples were given earlier in the .
