Vickie Wise, Age 13, Of Louisville, Ky., for her question;
What is the lightest substance in nature?
The world of nature includes all the wonders of our luxurious planet and far beyond. It extends to who know where beyond the solar system, the milky way and the reaches of outer space. In a quest for the lightest substance, we might have to travel far afield from our home in the heavens.
A substance is made of matter, either solid, liquid or gaseous. All matter is composed of atoms or molecules or ions or of even smaller fragments called subatomic particles. The weight of a substance depends upon the size of its particles and its density, which is the number of particles packed into a certain space.
On earth, the densest natural metal is osmium, and an ordinary house brick of this silvery substance weighs 56 pounds. The lightest earth substances, of course, are gases that have plenty of space between their separate atoms and m01ecules of matter. And the lightest of the gaseous elements is hydrogen.
The amount of hydrogen on earth is very slight. But this lightest element is abundant in the stars and in the gassy clouds between them. The density and weight of hydrogen gas are affected by temperature and the pressure of the earth's atmosphere. At sea level, a pint flask of hydrogen gas weighs about one thousandth of an ounce.
As it chills, hydrogen becomes a liquid and then a solid. Its weight and density increase. Hydrogen gas is about 15 times lighter than water vapor. Liquid hydrogen is 14 times lighter than water, and solid hydrogen is about 13 times lighter than ordinary ice. But nature extends throughout the universe, and out in space there are substances compared to which the hydrogen on earth may seem as heavy as lead.
The spaces between the planets and most likely between the stars are filled with an amazing stuff called plasma. It is a mixture of ions and subatomic particles and dynamic forces of electromagnetic energy. The particles of plasma are fragments of matter; hence, this filmy stuff between the heavenly bodies can be called a substance.
So far, science has sampled only small areas of plasma between the planets. Under the same conditions it has only half the weight of hydrogen, but plasmas may be denser and heavier closer to the sun. Plasmas out in space between the distant stars may be lighter. In fact, certain plasmas may be the lightest substances in the entire universe of nature.
A normal hydrogen atom has one proton in its nucleus and one orbiting electron. It is the smallest atom of the known elements. It also is the lightest atom, having an atomic weight of 1.008. But the hydrogen atom can lose its electron and become a smaller and still lighter ion. Plasma is composed of such ions, of smaller stray electrons and still smaller particles. Out in space, these fragments of matter are spread very thin indeed,. And no one knows the weight of the lightest plasma.