A covalent compound is formed when an element shares its valence electron with another element. This compound is formed between two non metals. Example:
An ionic compound is formed when an element completely transfers its valence electron to another element. The element which donates the electron is known as electropositive element or the metal and the element which accepts the electrons is known as electronegative element or non metal. Example:
No, why? Cause if you're winding up the clock it's basically doing what it needs to do. So there's no need for batteries.. I hope my sad sentence make sense :p