Democritus in 5th century B.C. Greece was walking along the beach with his teacher and asked the question “Is the water in the ocean continuous or is it made up of tiny uncuttable particles (atomos)?”
Leucippus, his teacher, probably turned the question back to Democritus, who answered “I believe that water is made of very tiny particles.” This is how the idea of atoms was born. For the next 2,000 years, the idea of atoms was held by few scientists or natural philosophers. Some believed that atoms would fill the universe, leaving no space for God.
The first key figure to show convincing arguments about atoms was a deeply religious man named John Dalton. Dalton was born into a modest Quaker family in Cumberland, England, in 1766. He earned a living as a school teacher, giving lessons as early as 12 years old.
As an adult, he moved to the industrial town of Manchester. Dalton used atoms to explain how different elements combined. Dalton knew that carbon could form carbon monoxide (one carbon and one oxygen) or carbon dioxide (one carbon and two oxygens).
When these compounds were formed, the carbon and oxygen weights were either 12 to 16 (CO) or 12 to 32 (CO2). Only if the oxygen atoms in CO2 were twice as numerous as those in CO could this be explained.
Dalton was presented to the King of England for an award and had to be dressed appropriately. He was given a scarlet robe, but Dalton being color blind saw it as black. (As a Quaker, he was forbidden to wear colorful garments.) Dalton’s atoms were used to explain the basic laws of chemistry.
Around 1900, the English physicist J.J. Thompson was doing experiments with cathode ray tubes. These devices were the ancestors of television picture tubes. Today we have flat screens but in the 1960s though the 2000s, televisions were comparatively thick.
Their picture tubes had a cathode that was at a high negative voltage with an anode at a positive voltage. The anode had a central hole. When negative voltage was applied to the cathode, it emitted small negatively charged particles that become known as electrons.
These electrons flew towards the anode at high speeds of many thousands of miles per second. Some smashed into the anode, but some flew through the central hole, going to the back of the tube which was coated with phosphor. The colliding electrons there made the phosphor glow. By applying electric or magnetic fields, the phosphor glow could be made to move around.
This was how the early televisions worked that allowed some of us to see the first humans to land on the moon in 1969.
With discovery of the electrons, a vision of the atom arose, the “plum pudding” model. The electrons were the plums, immersed in a positive pudding. (For the atom had to be electrically neutral and the “pudding” offset the negative charge of the electrons.) But who was to discard the pudding, representing our ignorance of the interior of an atom?
Ernest Rutherford was born in 1871 in Nelson, New Zealand, the fourth child of a dozen children. He graduated with honors in math and physical science from the University of New Zealand. Rutherford chose to do further studies in England at the Cavendish Laboratory under J.J. Thompson.
There, he made an important discovery: by wrapping uranium with layers of aluminum foil, he discovered two kinds of emissions. These were a softer emission called alpha and a more penetrating kind called beta.
He left Cambridge to go to McGill University in Montreal, Canada. There, Rutherford and Frederick Soddy found that a radioactive metal (thorium) decayed three ways, into thorium A, thorium B and thorium C.
Rutherford and Soddy discovered the concept of half-life, the time for half of a radioactive substance to decay. Rutherford returned to the University of Manchester in England where with others, he made his greatest discovery in 1911.
In bombarding gold foil with alpha particles (actually Helium nuclei), most alpha particles soared through but one in thousands turned around as if it had seen a “monster.” This “monster” was a tiny, highly charged positive nucleus that contains nearly all of the atom’s mass and all of its positive charge. Electrons fill most of the atom’s volume in the electron ‘cloud’.
So the plum pudding model of the atom was disposed of, replaced by an atomic model resembling our solar system with atomic nucleus as the sun and the outside electrons as the orbiting planets.
More discoveries were to come in the coming decades by physicists such as Neils Bohr, Wolfgang Pauli, Werner Heisenberg, Erwin Schrodinger and Louis de Broglie. It turns out that the world of the atom is exceedingly strange and mystical.
SKY SIGHTS IN THE COMING WEEK: Dawn begins about 4:30 a.m., sunrise is 5:47 a.m., midday is 1:14 p.m., sunset is 8:42 p.m. and dusk ends at 9:55 p.m. with sunlight lasting 14 hours and 55 minutes. Venus is too close to the sun to be seen. In the early morning sky, there are three outer planets with bright Jupiter and Saturn close together followed by Mars to the left. The moon will appear near Jupiter and Saturn in the morning hours of June 9.
Bob Doyle is a retired science teacher at Frostburg State University who is available to talk to adult and student groups about matters related to his columns. Contact him at firstname.lastname@example.org.