The Modern Concept of the Atom

Vocabulary: atomic number, atomic radius, Aufbau principle, chemical family, diagonal rule, electron configuration, Hund’s rule, orbital, Pauli exclusion principle, period, shell, spin, subshell

He stated that this was a mysterious force but never continued his research on it. Then in 460 B.C. there was a philosopher named Democritus. Democritus and his mentor Leocippus posed the question that if he broke bread into multiple pieces how many would breaks would it take until there was no more bread. He then was able to make a few theories being all matter was created of atoms and atoms are solid but not invisible. However, there was a man named Aristotle and many other philosophers who disagreed with Democritus and said matter was composed of four main elements. Earth, fire, air, and water. For example, a liquid was made of water and a stone was made of rock. Therefore, Democritus’s theory “ was rejected by Aristotle, one of the most influential philosophers of Ancient Greece; and the atomic theory was ignored for nearly 2,000 years.”(

Thomson did many experiments and found that the mass of one of these electrons was nearly 2000 times lighter than the element Hydrogen. Thomson then disproved Dalton in stating that atoms cannot be divided into smaller pieces. (Born,

Over the course of the last 5000 years, mankind’s knowledge has been constantly advancing. Chemistry, a branch of science, has experienced a tremendous leap and expansions since ancient Greek civilization. One of the major breakthroughs in the advancement in Chemistry was the creation of the Atomic theory, which laid a foundation for the modern-day Chemistry and future of science. The Atomic theory introduced the idea of atoms, which are defined as the discrete units of matter. There are five key scientists that significantly contributed to the Atomic model over a span of thousands of years. They are: Democritus, John Dalton, J.J. Thompson, Ernest Rutherford, and Niels Bohr.

“By 1687, he had theorized that gravity was a force that could hold objects, such as the moon, in orbit around the Earth, and he worked out equations to prove it” (Challenging Limits). He then calculated the laws of motion that held the planets in their orbits around the sun. Along with his research, he invented calculus, the method for working out the speed of an object at any given moment during its path. By the 20th century, scientist could demonstrate atoms and the tiny charged particles they contained called electrons. The electrons are virtually invisible, but Leeuwenhoek used them from an electron microscope that magnified ten million times. Allowing future scientist to develop the MRI scanner, a precise diagnostic tool used to learn about the work of the brain. In addition to the discovery of atoms and their electrons, a physicist by the name of Albert Einstein formulated the theorem E=mc2. Stating that energy resided in matter itself. With this, scientist learned that atoms are our greatest repository of energy. Scientist began to ask if they themselves, “if we could split atoms, could we release the new, limitless supply of energy” (Challenging Limits)? Soon, scientist did split atoms that released massive surges of energy, but also produced lethal radioactivity. This groundbreaking discovery provided a possible solution to what created the

Bohr is well known for his amazing research on the structure of the atom, he thought that maybe the hydrogen atom was based on the quantum theory that energy can only be transferred in one way, and he also thought that E. rutherford model had some problems, so he fixed

The Atomic Age, composed of complex and controversial issues, has forever changed our world and the way in which we live.

The atomic model that was accepted by the scientific community before Rutherford's experiment consisted of a group of positive charge surrounded by electrons to balance the negative charge of the electrons. In Rutherford's experiment, he found that there was a center to atoms, later to be named the nucleus. Rutherford created his own model after stating that Thompson's was incorrect.

Bohr's model, sometimes referred to as the planetary model, was able to provide explanation for concepts that were previously indescribable. Working off Rutherford's previous work, Bohr was able to successfully explain the spectrum of the hydrogen atom. While Rutherford's model focused mainly on the nucleus, Bohr paid greater attention to electrons. The previous model of the atom stated an electron was an orbiting planet. The problem in this flawed model was that the electron, moving in a circular path, would be accelerating.

What the three main particles of an atom? 3. Describe the nucleus of an atom. 4. Describe protons, neutrons and electrons: locations and charges. 5. How did the atomic theory develop and change?

Before Rutherford’s Geiger-Marsden experiment the most popular model of the atom was the “plum pudding model” developed in 1904 by the person who also discovered the electron in 1897, J.J. Thompson. It was the most common model of the atom and stated that electrons (plum) floated around with

One of Bohr’s most renowned accomplishments was his contribution to the atom. He discovered that the atom was a small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus. Most physicists run experiments in order to come

Throughout the centuries, there have been many people, from Democritus to Rutherford, that have changed the structure and the ideas of atoms. The atom has changed 6 times in the last 200 years(OI). Can you imagine that? Here are some ways the atom has changed.

As early as 400 BCE atoms were believed to be the building blocks of all matter. The atom is made up of three subatomic particles protons (p+) , neutrons and electrons ( e-). Protons have a positive charge and can be found in the nucleus along with the neutrons who have no charge. Protons, along with electrons, tell you the atomic number of any given element. A positron is the opposite of an electron and contains the same mass and spin of an electron but they have a positive charge. The sum of the number of protons and neutrons equals the mass number. The mass number connects matter to it’s antimatter, they are equivalent in value while the charges are opposite. This attraction cause the corresponding matter particles to annihilate each other.

After that theory scientists started Wondering about this theory and a lot of Scientists made up Models and conducted Experiments to Explain this Theory. In this report we will put our self’s inside Each scientist’s Shoe and see What has he discovered.