I am teaching the states of matter to first graders. I was looking for some demonstrations or hands-on activities to help the students understand the concept of a gas, since they can’t really see it.
—Megan, Maryland
First of all, I’m glad to hear your school has not relegated science to a back burner. It’s important to tap into students’ natural curiosity through learning activities appropriate for their levels of understanding and interest.
I shared your request with Peggy Ashbrook, a teacher, NSTA author, and blogger on science in the early years. Based on her experiences, she suggests:

• Check out the discussion on the NSTA community forums. In one post I shared some activities I do with preschoolers to give them focused experience with air, their most familiar gas.
• Here are a few ways for young children to explore air as something, not just ‘nothing.’ They can blow on their palms and feel their breath even though they cannot see it. Using empty, clean and dry dish detergent bottles they can move feathers around with the air that comes out of the bottle when they squeeze it quickly. They understand that something is pushing the feathers. After these experiences I ask students if air can hold up something heavy, such as a book. We try it and the book always falls to the table. Then we put our breath into zip-closing plastic bags and put the book on top of them. It doesn’t fall. Some children believe the bags alone can hold the book up and we try that. Then we try the inflated bags again and ponder why this way works. Not all of the children are interested or able to put into words what they think, but a few say, “The bags keep the air there so it can’t go away when the book is on it.”

• Because air is part of so many early childhood experiences–blowing bubbles, pumping up the deflated soccer ball, feeling a breeze, and learning to whistle–I think it’s okay to use the word ‘gas’ when we talk about air.
• Dance as a model of “there are small particles moving within the substance that we can’t see with just our eyes” might be useful in introducing the idea that there is more to solids, liquids, and gasses than meets our eyes, in a general way, such as we talk about “germs.” But I’m not sure if first graders are ready for understanding the distinctions between the molecular structure of the phases of matter.
• Definitely read Bill Robertson’s Science 101 column from the December 2008 issue of Science & Children: What causes the different states of matter? 
• What’s the Matter with Teaching Children About Matter? also appeared in this issue, along with other articles on the states of matter. 

Search for a topic at the K-4 level in SciLinks, for lists of websites for teachers and students. The teacher sites usually include lesson plans or demonstrations for the topic.  Here are a few from the topic States of Matter:

• Water and Ice
• Gas in a Bag
• Discovering Properties of Water

In addition to SciLinks, NSTA has other resources for learning and sharing ideas and background on content and teaching strategies appropriate for your students:

• As Peggy suggested, join the conversations in one of the Community Forums.
• Sign up to participate in the Elementary Listserve to ask other members for suggestions or to share yours. You can learn a lot by “lurking,” too.
• The Social Networking Dashboard keeps you up to date on NSTA’s presence on Facebook and Twitter, blog updates, and forums.
• Use the Learning Center to search for NSTA journal articles, webinars, books, and professional development resources.

Just be sure that your students realize that the ‘gas’ they’re learning about in these activities is not the same as ‘gasoline.’ (Even some of my seventh graders were a little confused with the language—gas as a state of matter vs. gas as a liquid fuel for cars.
 
Photo: http://www.flickr.com/photos/jeremyhiebert/6380128183/sizes/s/in/photostream/