Sometimes when you put two things together, they change into something new.  Chocolate + milk is chocolate milk.  Nice shirt + tomato sauce is dirty clothes.  Sun + snowman is water.  This is no different when talking about our building blocks, atoms. 

Chocolate milk, now that's the kind of chemistry lesson I like!

Sugar Bear, Public domain, via Wikimedia Commons

Atoms are the tiny building blocks that make up everything in the universe.  When you put two or more of them together, they can make something new.

Two lonely hydrogen atoms.

First of all we need a magic word that will mix two things together.  Wait, not magic.  A SCIENCE word.  Combine means to put together.  When you mix things, you may shake them, stir them, or just leave them alone together.  Snake + rabbit = fat snake.  Atoms can come together in a much different way.  They also like each other more than snakes and rabbits.

One happy hydrogen molecule sharing electrons.

Here are two atoms floating around all alone.  They both have the same name: H.  It's short for Hydrogen, which is a lot to say.  Oh look!  They found each other.  A molecule is when two or more of the same kinds of atoms come together.  H + H = H2.  Now they are a gas!  The atoms would carve that into a tree in the middle of a heart somewhere . . . if they were not so very small.

Even a water molecule has a shadow. Who knew?

No machine-readable author provided. David.gaya assumed (based on copyright claims)., Public domain, via Wikimedia Commons

Things do not have to have the same name to get along.  Here comes an H and another H and an O.  O is another word for one kind of gas that we can find in the air.  H is one of the kinds of gas that helps to make our sun bright and hot!  Even though they are very different kinds of atoms, they can still come together.  A compound is when different atoms come together.  H2O is water!  No, do not drink them!  They just met!


When atoms come together they become something new.  If they are the same, like an H and an H, they become a molecule.  If they are different, like an H and an H and an O, then they become a compound.  Are you excited to get out there and learn about all of the atoms and what they make when they come together? 

References: 

Chem 4 Kids.  "Compound Basics"  Chem 4 Kids, 2010.  <http://www.chem4kids.com/files/atom_compounds.html>