Here's why:
* Ionic Compounds: Many ionic compounds, especially those formed between a metal and a nonmetal, end in "-ide". For example:
* Sodium chloride (NaCl): The nonmetal chlorine forms the chloride ion.
* Magnesium oxide (MgO): The nonmetal oxygen forms the oxide ion.
* Binary Covalent Compounds: Some binary covalent compounds, those composed of two nonmetals, also end in "-ide". For example:
* Hydrogen sulfide (H₂S): Sulfur forms the sulfide ion.
* Nitrogen triiodide (NI₃): Iodine forms the iodide ion.
Important Note: While "-ide" is a strong indicator, it's not the only one. There are some compounds that do not end in "-ide" but are still part of the ionic or binary covalent categories. For example, ammonium chloride (NH₄Cl) is an ionic compound, but it does not have the "-ide" ending.
Therefore, while "-ide" is a useful clue for identifying a compound's class, it's important to use it in conjunction with other information, such as the chemical formula and the elements involved.