Look at that cute one over there.  You feel drawn to them.  Everything inside of you wants to be near them.  You move closer.  They move closer.  Soon, you are dancing together, sharing energy.  No, I am not talking about the school dance.  I am talking about carbon atoms, the stuff that holds all the small parts of your body together.  Electrons, the very, very small things that spin around atoms, are a little like arms.  They reach out past the middle, just like your arms reach out from your body.  They can also be used to hold onto other atoms, just like your arms would.  This makes for a great dance.

Not everyone is a good dancer.  Some people fall around all over the dance floor, looking for some help.  Lucky for them, there are some really good dancers out there.  If they reach out one of their arms, this dancer will give them one of their arms to hold on to.  Carbon is a really good dancer.  It has four electrons that are ready to hold on to another atom.  This means it has lots of "arms," so others can bond to it.  A covalent bond is when two atoms bond together by sharing a pair of electrons.  It's just like when two people dance and they both hold onto each other with one arm.  If a bad dancer holds a good dancer's hands, the bad dancer can learn some new moves! 

Tell you what, you hold me and I'll hold you.

Garry Knight, CC BY-SA 2.0 , via Wikimedia Commons

What makes carbon so great to dance with?  Why does it get along with so many others?  Well, what makes you get along with others?  People like people who have something to give.  This can be anything from time, to love, to food, to money.  Carbon atoms get along with so many others because they have things to share.  They have arms for other atoms to hold.  Valence electrons are the very small parts that float on the very outside of an atom and are easy for others to share.  Carbon has four of these so it can dance with up to four others at a time!  Your legs and arms are dancing and ready to dance with someone else.  Your moves catch everyone's eye and everyone wants to dance with you!

Now here's a guy with moves!

Airman 1st Class Justin Veazie, Public domain, via Wikimedia Commons

You do not only have arms to give.  You have deeper things to give too.  Inside of you, you have things like love, which can draw people to you, as well.  Atoms have electrons that move around them in all different places.  An electron shell is one of the layers where electrons can move around an atom.  Some may have only one of these and bigger atoms may have many of these.  It just so happens that carbon's shell on the outside has four extra parts to grab.  This way, other atoms will not poke around trying to take the deeper things that makes carbon what it is.  This would be like someone on the dance floor trying to break your heart, but this does not happen to our great dancer, Carbon.

Of course, you do not want to be the only one dancing, just like carbon does not want to just give all of its arms away.  It would be nice to get something back.  Other atoms also have electrons moving around their outside shell.  Even if it is fewer than four.  So, carbon will give something and the other atom will give something back.  A shared pair is when two atoms share two electrons.  This makes them both a lot happier than one stealing a part from the other.  They share!  You do a dance move and they do a dance move, back and forth.

This pair makes sharing look a lot harder than most.

Dancing is about sharing, just like bonding.  When you have a lot of great moves, other people will want to dance with you.  Carbon atoms have a lot of electrons so others come close to them.  These atoms have some moves of their own, so they give some back to make a shared pair.  If you copy these moves on the dance floor, you will have many happy people dancing all around you.

Reference:

Science for Kids.  "Covalent Bonds"  Kidipede, 2011.  <http://scienceforkids.kidipede.com/chemistry/atoms/covalent.htm>