Atom s Structure. Chemistry is the study of the structure, characteristics and behavior of matter. The basic

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1 AlMarzooqi 1 Hamad AlMarzooqi Professor Kafle ESL February 2013 Atom s Structure Chemistry is the study of the structure, characteristics and behavior of matter. The basic unit of matter is an atom, so what is an atom? What are atoms made up from? Do we really touch matter? Basically, everything around us consists of atoms; every matter is made up of atoms. In other words, atoms of different elements combine to make up matter. From my perspective, atoms make up matter, and they are divisible into smaller particles that vary in charge and magnitude. I really think knowing the structure of an atom is crucial for knowing the elements. In the 5th century B.C. the Greek philosophers Democritus and Leucippus proposed that matter was made up of tiny, indivisible particles called atoms. The word atom means indivisible in Greek. The reason for this assumption is that nothing can come from nothing. Essentially, atoms were thought to be indivisible, but due to the hard work and determination of the scientists (such as John Dalton, Thompson, Bohr and many more), atoms are known today to be made up of even smaller indivisible subatomic particles. In the first decade of the 18th century, John Dalton, was one of the first scientists who generally contributed in developing the current understanding of atoms. Dalton proposed the first modern atomic theory. Dalton's theory basically consisted of five main points: 1) Atoms combine in different ways to form matter. 2) For a given element, all of its atoms are

2 AlMarzooqi 2 indistinguishable in its properties and mass, whereas they differ in mass and characteristics for atoms of different elements. 3) Atoms are indivisible; they cannot be created nor destroyed. 4) In chemical reactions, atoms of the same or different elements can be combined. 5) In chemical reactions, these small particles combine with each other in simple, whole number ratios to form combined atoms. His theory formed the bases of modern chemistry. Although some parts of the theory were proven wrong, scientists kept updating it over the years. Atoms were thought to be the smallest particles of matter until Thomson discovered the electrons while he was working with cathode rays. The experiment that he conducted consisted of a tube that is a confined glass container, and there were two electrodes that are kept apart by a vacuum medium. A current was passed across the electrodes; cathode rays were generated, creating a glowing patch where they hit the opposite sides of the tube. During the tests, he observed that the electric field had been reflecting the cathode rays. He concluded that these rays, rather than being a form of light, were composed of a nearly weightless, negatively charged particles that he called electrons. His model was widely known by the plum-pudding atom, where the structure of the atom was thought to be made of a sphere with positive charge pudding and negative charges sprinkled all over the sphere just like the plum. However, this model was proven wrong by one of the bright scientists. An English chemist and physicist Ernest Rutherford who was known as the father of nuclear wanted to prove Thomson s plum pudding model by conducting an experiment. The results that Rutherford got from the experiment proved Thomson s model to be incorrect. Rutherford s experiment is known as The gold foil experiment, where he aimed a beam of alpha particles (heavy, positively charged particles) at a gold foil. Surrounding the gold foil was a fluorescent screen that would glow when the particles collide on the screen. Rutherford

3 AlMarzooqi 3 reasoned that the way the alpha particle travel throughout the gold foil would provide him with information regarding the structure of the gold atoms. While conducting the experiment, he observed that most of the alpha particles passed the gold foil without any degree of deflection, he also noticed that a few alpha particles where deflected at different angles, and some were reflected backwards as well. Rutherford concluded from these observations that the atom is mostly consisted of empty space since the positively charged particles travelled through the gold foil without a deflection. Regarding the small portion of alpha particles that were deflected and reflected, he concluded that an atom must have a center that contains most of the atoms weight with a positive charged particles, that he called as protons, which was responsible for the deflections that happened. The atomic structure is nowadays known and accepted by the science community to consist of a center of positive charge and it accounts for most of the atoms weight. There are two subatomic particles in the nucleus, which are the proton and neutrons. The protons are positively charged particles and the neutrons are neutral particles, and the electrons which have a negative charge revolve around the nucleus in orbitals. All of this evidence serves to prove that my perspective of atoms was correct. An interesting fact about atoms is that we actually don t touch anything because all electrons have negative charges, and negatives repulse negatives (magnetically). Therefore, at a subatomic level we actually never touch anything. The part of the atom that contains mass, the nucleus, never touches another nucleus. The electromagnetic force between atoms keeps the nucleus's from ever touching. For example: The electrons in your fingertips repel the electrons in the keyboard keys allowing the key to be pressed. To sum it up, knowing the structure of an atom is crucial especially to chemists; a lot of phenomena s can only be explained by understanding the structure of an atom. Thanks to those

4 AlMarzooqi 4 scientists who participated in improving the atomic theory, which made our lives easier and clearer.

5 AlMarzooqi 5 Work Cited Takada, K. (2004, May 15). Discovery of atoms. Retrieved from Atomic theory. (n.d.). Retrieved from Theory.html The atom in history. (n.d.). Retrieved from The gold foil experiment. (n.d.). Retrieved from