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(a) Why does helium have zero valecy? ...

(a) Why does helium have zero valecy?
(b) Name the secientist and his experiment to prove that nucleus of an atom is positively charged.

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(a) Atomic number (z) of helium is 2 .Its electronic configuration is K(2) .This means that its atom has completely filled shell which is the only shell it has .Therefore valecny of the element is zero .
(b) The scientist is Rutherfored and the experiment is known as `alpha` paricle scattering experimine t.Fopr details consult section 4.4
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