To determine the fraction of the helium-4 atom's mass contributed by the nucleus, we need to calculate the mass of the nucleus and compare it to the total mass of the atom.
The helium-4 nucleus consists of two protons and two neutrons. The mass of a proton is approximately 1.67×10^(-24) grams, and the mass of a neutron is also approximately 1.67×10^(-24) grams.
The total mass of the helium-4 nucleus is then: (2 protons) × (1.67×10^(-24) g/proton) + (2 neutrons) × (1.67×10^(-24) g/neutron) = 6.68×10^(-24) g.
The mass of the two electrons is given as 9.11×10^(-28) grams.
To calculate the fraction of the helium-4 atom's mass contributed by the nucleus, we add the masses of the nucleus and the electrons, and then divide the mass of the nucleus by the total mass:
Fraction contributed by nucleus = (mass of nucleus) / (mass of nucleus + mass of electrons) = (6.68×10^(-24) g) / (6.68×10^(-24) g + 9.11×10^(-28) g) = 0.99986
Therefore, the fraction of the helium-4 atom's mass contributed by the nucleus is approximately 0.99986 or 99.986%.