Question

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

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

a.The radius of helium atom is 3.1 x 10^-11m; the radius of the nucleus is 2.5 x 10^-15m. What fraction of the spherical atomic volumeis occupied by the nucleus

b. The mass of a helium-4 isotope atom is 6.64648 x 10^-24g and each of the two electrons has a mass of 9.10939 x 10^-28 g. What fraction of this atom’s mass is contributed by its nucleus?

Homework Answers

Answer #1

a)

volume of atom = (4/3)*pi*R^3

= (4/3)*3.14*(3.1*10^-11)^3

= 1.25*10^-31 m^3

volume of nucleus = (4/3)*pi*r^3

= (4/3)*3.14*(2.5*10^-15)^3

= 6.54*10^-44 m^3

fraction = volume of nucleus / volume of atom

= (6.54*10^-44 m^3) / (1.25*10^-31 m^3)

= 5.23*10^-13

Answer: 5.23*10^-13

b)

mass of electrons = 2* mass of each electron

= 2*9.10939*10^-28

= 1.821878*10^-27 g

mass of nucleus = mass of atom - mass of electrons

= 6.64648*10^-24 - 1.821878*10^-27 g

= 6.644658*10^-24

fraction = mass of nucleus / mass of atom

= (6.644658*10^-24) / (6.64648*10^-24)

= 0.999726

Answer: 0.999726

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