Lesson 5: Atomic Model

• An atomic model represents what the structure of an atom should look like, based on what we know about how atoms behave.
• Most atomists like Democritus and advocates of atomic theory believed that the atom was a fundamental, indestructible, indivisible particle. This is sometimes known as the billiard ball model (structureless atom) concept of the atom, wherein the atom is an incredibly small but smooth and whole object.
• Prout’s model proposed by an English physician, William Prout. Atomic masses of the elements known then were integral multiples of the atomic mass of hydrogen.
• Later in 1897, Joseph John Thomson published the idea that electricity was in particles that were part of the atom. Experimenting with cathode rays, he established the mass and charge properties of these particles. These particles were named electrons. In 1904, he came up with the plum-pudding model, which was an idea of what the atom looked like based on his experiments.
• In 1911, Physicist Ernest Rutherford, a student of Thomson, theorized that the model proposed by Thomson did not explain the deflection of alpha particles. Therefore, he devised his own model with a positive nucleus at the center and electrons revolving like planets at a distance around it.
• Dalton Model ( Billiard Ball Model ): 1803, John Dalton believed that an atom was an indestructible particle with no internal frame.
• Thomson Model ( Plum Pudding Model ): 1897, J.J. Thomson disovers the electrons. He believed electrons were embedded in positive charge sphere.
• Rutherford Model - 1911, Ernest Rutherford discovers that there is a dense, positively charged nucleus. Electrons go around the nucleus.
• Bohr Model - 1913, Niels Bohr enhances Rutherford's model by having electrons move in a circular orbit at fixed distances from the nucleus.
• Each element has unique atomic properties that define its behavior and characteristics. These properties include atomic mass, atomic radius, ionization energy, electronegativity, and chemical reactivity.
• Atomic mass refers to the difference between the mass of an atomic nucleus and the sum of the masses of its individual protons and neutrons.
• Atomic radius refers to the measurement of the size of an atom. It is typically defined as the distance between the nucleus at the center of an atom and the outermost shell of its electrons.
• Ionization refers to the process in which an atom or molecule gains or loses electrons, resulting in the formation of ions.
• Ionizing Radiation - High-energy radiation, such as X-raysor gamma rays, can also cause ionization by removingelectrons from atoms or molecules.
• Ions - an atom or a molecule with a net electrical charge.
• Electronegativity is a measure of the ability of an atom to attract electrons towards itself in a chemical bond. It is a property of an atom that indicates its relative strength in attracting shared electrons in a covalent bond.
• Chemical reactivity is the ability of a substance to interact chemically with a second substance. Reactivity will often happen when two or more substances are physically mixed together or come in contact with each other.