I'm suppose to write out reactions where atoms send out alpha radiation and decay. The book uses the 4-2 H, 4 as nucleon number and 2 as proton number, but isn't that wrong? The mass of helium is greater than the alpha particle due to two electrons? Shouldn't they use a different notation for the alpha-particle other than that for helium?
Alpha particles are essentially the same as a deionized Helium atom. The mass of the electron pair can be neglected because the mass of an electron is significantly smaller than that of the protons and the neutrons in the nucleus, so don't have much of an effect for simple purposes. See http://en.wikipedia.org/wiki/Proton-to-electron_mass_ratio which shows the scale of the difference.