Helium+balloons+Sulfur+hexafluoride

In your post list three things you knew and three things you learned.

Period #1

Afflebach, Kathryn Brindza, Miranda Burke, Justin Bush, Monica Cardello, Jack Dickman, Amanda Feldmann, Gregory Hildebrand, Tijay Hodgson, David Ilko, Jessica Linburg, Jebidiah Miljevic, Djordje Nizinski, Allison Nophlin, Afryea Ochiobi, Julia Palmer, Maxfield Pathak, Rudri Smith, Anjuli Stephens, Abbigail Than, Veasna Tran, Dat Villarose, John Waltersdorff, Kara Kevin Myers

Period #4 Adams, Kathryn Bahn, Michael Chen, Yanqi-Tyson Conrad, Caitlin Crowell, Travon Davies, Seth Emery, Nicholas English, Jacob Grobosky, Ryan Harter, McKenna Hipkins, Garrett Hoover, Joshua Reed, Jason Smith, Amelia Snowadzky, Morgen Snyder, Justin Sprenkle, Ryan Strickler, Ryan Tariq, Wareesha Truax, Kirsten Turnow, Cody Visco, Nathan Zunic, Samantha