Bob Doyle, Columnist
One of the most important words in science is “element.” For thousands of years, the recognized elements were air, fire, water, earth and quintessence.
Aristotle, the most important scientist of ancient Greece developed his list based on natural motion.
If an object tended to rise, (such as smoke), it was made of air and/or fire. But if an object tended to fall, it was made of Earth, water or some combination of these two elements.
The fifth element, quintessence was reserved for the heavenly bodies, which moved in circular paths across the sky.
Quintessence was an eternal element; any bodies made of it would never deteriorate nor show any signs of imperfection. So the sun and moon were made of quintessence and had to be flawless.
During the Renaissance, scientists began to question Aristotle’s ideas. Telescopic observations showed the moon to a rugged world with many craters, mountains and flat plains; the sun was scarred by dark blotches (sunspots), that arose and then faded away weeks or months later.
The first scientist to redefine “element” was Robert Boyle. With the advent of modern chemistry in the late 1700’s and early 1800’s, the idea of atoms was revived. Several dozen elements were identified.
An element was regarded as an atom, the smallest unit of matter that retained its chemical properties. Many elements tended to combine with other elements to make compounds (Water or H2O has two hydrogen atoms attached to one oxygen atom).
Using electricity or heat, many compounds could be broken down into separate elements.
Today, an element is an atom with a certain number of protons in its nucleus or center. The nucleus is about 1/20,000 the width of the atom itself. But the nucleus contains all the positive charges (protons) and nearly all the mass of an atom.
Most of an atom’s volume is in its electron cloud, containing tiny negative particles that circulate about the nucleus. If the nucleus is expanded to the size of a pea, the electron cloud would be a sports area (like Oriole Park in Baltimore).
The chemical properties of an element are determined by the number of outer electrons. Most elements’ outer electron shell can hold eight electrons. If an element has three or fewer outer electrons, the element is a metal. But if an element has four or more outer electrons, it is a non-metal.
Metals tend to give away their outer electrons while non-metals seek more electrons to fill their outer shells. The elements with filled outer shells (helium, argon, neon, xenon) seldom react chemically and are called Noble Gases.
Life on Earth relies heavily on a dozen or so elements. These elements of life are the lightest elements and quite abundant in the Earth’s crust. Since life likely arose in the waters of the Earth, most life forms contain a fair portion of water, making hydrogen the most abundant element in our bodies.
Hydrogen is also the most abundant element in the universe with most stars being largely hydrogen.
The second most abundant element in life forms is oxygen, combined either with water or circulating as a molecule with two oxygen atoms bonded together.
In third place is carbon, whose exceptional combining properties makes carbon the architect of life with a huge number of carbon containing compounds in our bodies, plants and animals.
In fourth place is nitrogen, essential for building proteins. Another key element is iron, which latches onto oxygen in the molecule hemoglobin.
Our bones and teeth rely on calcium and phosphorus, a metal and non-metal. Sodium, potassium and chlorine are present in our body fluids to allow our nerves to transmit electrical signals.
Besides the key body elements, our technology also relies heavily on silicon, copper, aluminum and manganese.
SKY SIGHTS AHEAD: In this first week of winter, Venus drifts lower in the western twilight as her setting time drops from 7:10 p.m. to 6:35 p.m.
The planet Jupiter rises in the east before Venus sets. With flat east and west horizons, you may be able to glimpse them both about 6:45 p.m.
This Tuesday, the moon will be rising about midnight and is best seen in the morning predawn sky. My next column will list the best sights for 2014, including two lunar eclipses (mid-April and early October.)
Bob Doyle invites any readers comments and questions. E-mail him at firstname.lastname@example.org . He is available as a speaker on his column topics.