Atoms have positive charges? or nuclei? Rutherford conducted the infamous gold foil experiment from which he concluded an atom mist contain a dense positively charged part with a orbiting shell of negative parts. That model was refined many times to form the current model of the atom.
It always points towards the products.
Reactant is the left side. 4+3=7
Answer:
228
Explanation:
alpha decay is removing alpha particle 
2 number of protons, 4 mass number = 2 protons + 2 neutrons
We have
90 protons and 142 neutrons
<u> - 2 protons - 2 neutrons</u>
88 protons 140 neutrons
Mass number of new (daughter) atom = 88 +140 = 228
I think the answer is hmmm I think