Find actual atomic mass of helium

Answer 1

Find the actual mass of He.

The massively predominant isotope is He-4 whose Fractional abundance is = 0.999998.

therefore He has 2 protons, 2 neutrons and 2 electrons.

the mass of an electron is 9.11 x 10-31kg

the mass of a neutron is 1.675 x 10-27kg

the mass of a proton is 1.672 x 10-27kg

mass of 2 electrons = 2 x 9.11 x 10-31kg = 1.822 x 10-30kg

mass of 2 neutrons = 2 x 1.675 x 10-27kg = 3.55 x 10-27kg

mass of 2 protons = 2 x 1.672 x 10-27kg = 3.344 x 10-27kg

Actual atomic mass of He = 1.822 x 10-30kg + 3.55 x 10-27kg + 3.344 x 10-27kg = 6.896 x 10-27kg

Answer 2

helium has an atomic mass of 4.0026 amu. each amu = about 1.66 x 10^-24 grams

mass = 4.0026(1.66 x 10^-24) = about 6.6463 x 10^-24 grams

or = 6.6463 x 10^-27 kilograms (1 kg = 1000 grams)

this is for a helium atom with 2 neutrons, a naturally occurring isotope.

there is another stable isotope but the usual atomic mass is given for the 2 neutrons isotope.

you can pretty much ignore the mass of the electrons, as they're negligible compared to the mass of the protons and neutrons.

A threesome went to dinner, an electron, proton and a neutron. After the meal they began to pay the bill. The waiter stopped the neutron and said "No charge for you."