Question

How are covalent bonds formed?

Answer 1

Atoms bond together to become stable, or filling their 'shell', and sometimes that means bonding covalently. Covalent bonds are where atoms share their valance electrons with one another. In the picture you can see two separate Cl atoms; they are both unstable with 7 valance electrons. In order to stabilize they need 8, so they share.
I like your question; however, it should be posted in they correct place. This sounds like Chem to me, not history.