Originally Posted by Don Baldwin

tc,

Not a "science person"?

A helium atom isn't twice as big as a hydrogen atom...it's actually smaller. A helium atom IS four times as heavy with 2 protons and 2 neutrons.

"The diameter of the nucleus of an atom -- the protons and neutrons in the center -- is 10,000 times smaller than the total diameter of the atom. This space contains electrons flying around the nucleus, but is mostly empty. Thus, we can compare the relative distances inside the atom and the comparative size of the atom.Apr 24, 2017"

"An atom is a million times smaller than the thickest human hair. The diameter of an atom ranges from about 0.1 to 0.5 nanometers (1 × 10−10 m to 5 × 10−10 m). "

"As you move from left to right across a period, the number of protons in the nucleus increases. The electrons are thus attracted to the nucleus more strongly, and the atomic radius is smaller (this attraction is much stronger than the relatively weak repulsion between electrons).Apr 25, 2012"

Atomic Radius of the elements

Helium31 pm
Hydrogen53 pm

The force pulling on the electron from 2 protons shrinks the electron cloud in He compared to the weaker pull from 1 proton in H.