In Sonic the Hedgehog 4: Episode 1 for the PS3, Xbox 360, Wii, and iPhone/iPad, there are a total of seven Chaos Emeralds you can collect, one for each level.
To get the Chaos Emeralds, you need to access each levels Bonus Stage. To get to the Bonus Stage of any level, you’ll need to collect 50 rings in that stage. Once you do, a giant ring will appear at the end of the stage. Jump through the giant ring and you’ll be taken to the Bonus Stage for that level.
Each Bonus Stage has a Chaos Emerald at the end. Once you get the Chaos Emerald for that level, the Bonus Stage will no longer be accessible.