Question

Helium is the lightest noble gas and the second most abundant element (after hydrogen) in the universe.


 a. The radius of a helium atom is 3.1 x 10^-11 m; the radius of its nucleus is 2.5 x10^-15 m. What precent of the atomic volume is occupied by the nucleus?


b.the mass of helium -4 atom is 6.64648 x 10^-24g, and each of its two electrons has a mass of 9.10939 x 10^-28g. What present of this atoms mass is contributed by its nucleus?

C. In one or two complete sentences, describe what your answers reveal about atomic structure

Answer 1

a)

radius of a helium atom = 3.1 x 10^-11 m

the radius of its nucleus = 2.5 x10^-15 m.

volume = 4/3 x pi x r^3

precent of the atomic volume = (2.5 x 10^-15)^3 / (3.1 x 10^-11)^3

precent of the atomic volume = 5.2 x 10^-13

b)

weight of 2 electrons in helium = 2 x 9.10939 x 10^-28g

                                                = 1.82 x 10^-27 g

weight of helium = 6.64648 x 10^-24g

mass of nucleus = 6.64648 x 10^-24 - 1.82 x 10^-27

                            = 6.64 x 10^-24

fraction of mass contributed = 6.64 x 10^-24 / 6.64648 x 10^-24

                                              = 0.9997