chemical bond

A chemical bond is the "glue" that holds atoms together — the attraction that links them into everything from a water droplet to a diamond to the cells in your body. It isn't a piece of string or a tiny rod; it's a tug-of-war between the negatively charged electrons of one atom and the positively charged nuclei of its neighbours, settling into an arrangement that's more stable, and lower in energy, than the atoms standing apart.

Atoms strike that bargain in three main ways. In a covalent bond they share a pair of electrons between them, like two children each gripping the same rope — this is how water and most of life's molecules are held. In an ionic bond one atom hands an electron over to another, and the two, now oppositely charged, cling together by sheer electrical attraction — table salt is the classic case. In a metallic bond a whole crowd of atoms throws their outer electrons into a shared "sea" that everyone floats in, which is why metals conduct electricity and bend without snapping.

Here's the part people often miss: bonds store energy, and breaking them always costs energy rather than releasing it. When fuel burns or food is digested and energy pours out, it isn't because old bonds broke — it's because the new bonds that form afterward are even stronger and more stable, and the surplus is set free as heat.