Helium DOES have mass.
More Info: The noble gas helium has a mass. On the periodic table, helium appears at atomic number 2. This means one atom of helium has two protons and two neutrons in its nucleus. Its position on the periodic table tells us that it also has two electrons. Though protons, neutrons, and electrons are often thought of only as electrical charges, they are actually particles. A particle has mass, and the sum of these particles’ masses defines an element’s mass.
What Are Masses? What Are Weights?
Though often used synonymously, mass and weight are different concepts for chemists and physicists. Mass is the term for a body’s quantitative resistance to acceleration. It is often indirectly measured. Despite situational and conditional differences, mass does not change. Weight is a measurement of force, which is equal to a mass multiplied by an acceleration constant. Though dubbed a constant, this acceleration’s value actually varies depending upon given circumstances. For weight, the acceleration constant is due to gravitation on a planet, moon or other enormous celestial body. Therefore, an object’s weight will change depending on this value. A person weighs a certain amount on the surface of the earth, and that person has a different weight on the surface of the moon. Weight is a quantity dependent upon mass. All objects that have weights therefore also have masses. Thus, elements have both masses and weights.
How Can You Find Helium’s Mass?
The periodic table has a listing for helium’s relative atomic mass which is 4.0024 u. This value is the average value for an element’s mass in standard atomic units. This value is also the amount of kilograms that can be found in a single mole of the element. The Avogadro constant tells you the number of atoms in a single mole. Using basic mathematics, you can therefore determine the value of a single atom’s mass by dividing the relative atomic mass by the Avogadro constant. The resulting incredibly small number is the average mass of an atom of helium in kilograms.
Force and Mass
NASA Glen Research Center
Forces on a Falling Object
Georgia State University-Department of Physics and Astronomy
University of Wisconsin Madison