Case Study

Case:

History of Atomic Structure  & the Benefit of Knowing Isotope Symbolism

Case presentation:

For years the human mind has been captivated and petrified by a single question, “ what is the world made of? ” I mean we know for example that a wooden table are made up of joining wooden stick that are nailed to one another. But what is the world made up of? Is a very mysterious question for a long time. But now, we all know that Atoms are the foundation of everything. The word atom is derived from the Greek word “atmos” which mean indivisible. Where now we know that atom is the basic “building block” for all matter in the universe. Today I’m going to discuss the historical timeline behind the “finding” of understanding atom, through atomic study that resulted as an atomic theory.

Atomic theory is the scientific theory study of the nature of matter. The theory states that matter is made up of small particles called atoms. Prior to this theory, matter was thought to be able to be divided into any small quantity. 442 BC, Democritus, a Greek philosopher was the pioneer to the study of atom in the first place, where he co-originated the thought with his teacher, Leucippus that all matter is composed of indivisible elements. Long after his “rough” theory was proposed. Thousands of years later, at 1803 John Dalton, a British chemist and physicist, developed a theory that was based and support Democritus perspective on atomic study. John Dalton state “matter is simply composed of atoms of different weights and is combined in ratios by weight” beside that he also proposed that these atoms are spherical, and are in motion.

        1898, JJ Thomson (Sir Joseph John Thomson was an English physicist) discovers the electron, using properties of cathode rays.  Cathode ray tube is a vacuum tube containing one or more electron guns, and a phosphorescent screen used to view images. It is used to accelerate and deflect the electron beam onto the screen to create the images. which enabled scientist to observe and analyze the projectiled images.  In 1911 Ernest Rutherford who performed many experiments to explore radioactivity did an experiment in which he discovered that the atom must have a concentrated positive center charge that contains most of the atom's mass. He suggested that the nucleus contained a particle with a positive charge which we now know as proton.

1913, Niels Bohr (a Danish physicist who made foundational contributions to understanding atomic structure and quantum theory) developed the Bohr atomic model,  in which electrons  orbits around the nucleus, and chemical properties being determined by how many electrons are in the most outer orbits (Valence shell electron). The last “ingredient” of an atom which is the Neutron component was discovered by James Chadwick in 1931. He was later awarded the 1935 Nobel Prize in Physics for his discovery of the neutron.

Now we know that atom of each element is made up of electrons, protons and neutrons. All atoms of the same neutral element have the same number of protons and electrons, but the number of neutrons can differ. Atoms of the same element but different neutrons are called isotopes. Because of these isotopes it becomes necessary to develop a notation to distinguish one isotope from another. By being able to identify the different number between them we can identify the type of atom it is without even looking at the symbol. The atomic symbol has three parts to it:

1. The symbol X: the usual element symbol

2. The atomic number A: equal to the number of protons (placed as a left subscript)

3. The mass number Z: equal to the number of protons and neutrons in the isotope (placed as a left superscript)

Example: Consider two isotopes of gallium, one having the 37 neutrons and the other having 39 neutrons. Write the atomic symbols for each isotope. Solution: