A couple of questions involving atomic bombs...

Just so I don’t get griped at, I tried to find this information. All I got was confusing formulas & such. So here are my questions:

1.) If you stand next to a chunk of Uranium, will you get radiation poisoning? Or does it have to be in a bomb? I suppose if you throw it at someone, you might give them a nasty bruise….

2.) Is one atom split in a nuclear bomb, or multiple atoms? Is one really that powerful?

For the record, I thought of these questions when I was half-asleep last night.