What is alpha decay?
Alpha decay is a nuclear change process which produces an alpha particle. Alpha particles are He atoms which have had their electrons removed giving them a +2 charge.
Alpha decay will cause transmutation to occur - this means that one element will turn into another element as the alpha particles are released.
Important connection to history - Rutherford used a radioactive substance (Polonium) in his gold foil experiment when he discovered the nucleus.
Here is a video which discusses how to write and balance an equation for an alpha decay process.