Difference between 2nd and 3rd Gen

Hello,

I was wondering what the diffrence between the 2nd and 3rd gen was,

My iPod has 8Gb of storage and can record voice memo's

It is also not the 1st gen, It's either 2nd or 3rd, Can anyone help.

Also the iPod is not in my possision i sold it to someone and I was wondering what generation is was so I could use iCloud.

Thanks