From the\u00a0high school chemistry point of view, there are two types\u00a0compounds:\u00a0 ionic and covalent.\u00a0 Ionic names start with a\u00a0metal; covalent names contain only nonmetals.<\/p>\n
What is a metal and what is a nonmetal?\u00a0 There are two ways to answer that question.\u00a0 Talking about elements on the periodic table, the metals are on the left.\u00a0 They\u00a0stretch all the way to a\u00a0boundary that starts at the 13th column and\u00a0zigzags down to the right.\u00a0 Usually it’s a red line, but if it’s not on yours, here’s the boundary:<\/p>\n
boron is a nonmetal, but aluminum is a metal;<\/p>\n
silicon is a nonmetal, but germanium is a metal;<\/p>\n
arsenic is a nonmetal, but antimony is a metal;<\/p>\n
tellurium is a nonmetal, but polonium is a metal.<\/p>\n
Anything to the right of that boundary is a nonmetal.\u00a0 Once again, anything to its left is a metal.<\/p>\n
The important concept about forming an ionic compound – such as calcium chloride – is that the nonmetal “charges” (or combining capacities) must equal the metal charges (or combining capacities, depending on how you see it).<\/p>\n
Some periodic tables have these charges right on them: \u00a0they’re either positive or negative, and most are between 1 and 5.\u00a0 However, old ones often don’t.\u00a0 If yours doesn’t, here’s how to tell what the combining capacity is:<\/p>\n
| Column<\/td>\n | H, Li, Na, etc<\/td>\n | Be<\/td>\n | B<\/td>\n | C<\/td>\n | N<\/td>\n | O<\/td>\n | F<\/td>\n<\/tr>\n |
| Combining Capacity<\/td>\n | 1<\/td>\n | 2<\/td>\n | 3<\/td>\n | 4<\/td>\n | 3<\/td>\n | 2<\/td>\n | 1<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n To our example:\u00a0 calcium chloride.\u00a0 Calcium is under Be, so its combining capacity is 2.\u00a0 On the other hand, chlorine is under F, so it has a combining capacity of 1.\u00a0 Since the nonmetal combining capacity has to equal the metal, we need two chlorines.\u00a0 2×1=2, which equals the calcium’s 2 (calcium being the metal, of course).\u00a0 The formula for calcium chloride is, therefore, CaCl2<\/sub>.<\/p>\n By that same reasoning, the formula of sodium sulfide is Na2<\/sub>S. Finally, the formula of magnesium oxide is MgO (since both Mg and O have the same combining capacity, you only need one each).<\/p>\n We’ll make\u00a0some observations:<\/p>\n 1)\u00a0 When written in words, the names are in all lower case.<\/p>\n 2)\u00a0 When written as formulas, only the first letter of each atomic symbol is capitalized.\u00a0 For example, hydrogen is written H, but sodium is written Na.<\/p>\n 3)\u00a0 When naming a simple ionic, the second atom (the nonmetal) gets an -ide ending.<\/p>\n 4)\u00a0 The sunken middle portion of the table (which starts on the left with Sc) we didn’t discuss this time.\u00a0 Its members\u00a0get a slightly different treatment, which we’ll address soon.<\/p>\n |