What classifies something as Ionic or covalent?

Answer 1

When two atoms come together and form a bond, they can do so by either sharing electrons or by taking/donating them. When they share electrons, electron density is smeared out between the atoms. (You can think about an electron bouncing back and fourth between the atoms.)

When an ionic bond forms, one atom gives up one electron to another. When an atom gives up an electron, it becomes positive, and when an atom gains an electron it becomes negative. When this happens, you end up with one positive atom and one negative atom. Just like when opposite ends of a magnet attract one another, so do the positive and negative atoms. These opposites attract and stick together.