Atomic Models and Theories PDF

ATOMIC MODELS AND THEORIES  Objectives Trace the evolution of the conception of the atom Explain Dalton’s modern atomic theory Describe the different atomic models and the experiments done to determine the subatomic particles  "What makes up everything?" The early atomic...

ATOMIC MODELS AND THEORIES  Objectives Trace the evolution of the conception of the atom Explain Dalton’s modern atomic theory Describe the different atomic models and the experiments done to determine the subatomic particles  "What makes up everything?" The early atomic ideas came from philosophers. “Primal” matter made up matter. This idea was thought by Thales, Anaximenes, and Heraclitus Aristotle also proposed that all materials are composed of four elements-fire, water, air, and earth—in different amounts. Democritus and his teacher Leucippus proposed that matter is composed of very tiny particles that cannot be further divided. They called this indivisible bit of matter “atomos," which became the basis for the modern word of the building blocks of matter, the atom. They described these pieces to have different forms and they combined in different ways to give rise to different materials found all around us.  Atom building blocks of matter composed of proton, electron and neutron Bohr’s Atomic Model  Atomic Structure Atoms have a nucleus that contains Protons and Neutrons An atom is made of mostly empty space  Atomic Structure Electrons are contained in shells that surround the nucleus Protons have a positive charge Electrons have a negative charge Neutrons are Neutral Bohr used Max Planck's theory on quantized energy of the electrons. He explained that electrons do not need to emit energy while moving around the nucleus. Instead, electrons are in a state called the ground state where they are stable, and their energy is fixed. This visualizes the electrons to have a restricted orbit around the nucleus. This is just like how the planets are located at certain orbits around the sun. He added that electrons become excited state when they absorb energy and move to a higher energy level. These electrons eventually go back to being in the ground state, release energy in the form of heat or light, and go back to its original state.  Valence Electrons Each electron shell can hold a Electron Number of certain number of electrons Shell Electrons 1 2 Electron shells are filled from the inside out 2 8 3 8 Noble Gases have full outer electron shells 4 18 5 18 All other elements have partially filled outer electron 6 32 shells 7 32  Valence Electrons The electrons in the outer most electron shell are called valence electrons The shell containing electrons that is furthest from the nucleus is called the valence shell Model of an Atom  Atomic Number and Mass The experiment of Rutherford helped investigate the nucleus. According to his studies, the mass of an atom is concentrated in its nucleus. The positive charge in it is due to the presence of proton. The number of protons in an atom states what element an atom is. The number of electrons equals the number of protons. If electrons are removed from or added to a neutral atom, the same element will become a charged particle and ion is formed. Cation, the ion with a positive charge, is formed when the electron is removed from an atom. Anion, the ion with a negative charge is formed when the electron is added to an atom. The atoms of different elements have different number of protons as well as atomic number. The atomic number serves as the "numeric identity" of the element. Therefore, no two elements have the same atomic number.  Bohr - Sommerfeld Model Niels Bohr created a visual model of the atom to make them easy to understand A Bohr Model contains a central nucleus surrounded by electron shells  Bohr - Sommerfeld Model Arnold Johannes Wilhelm Sommerfeld expanded the idea of Bohr’s Model Quantum Mechanical Model of an Atom  Objectives Describe the quantum model of an atom Describe the behavior of electron using the quantum numbers and electron configuration  Stability Noble gases are usually unreactive This is because they have full valence shells An element with a full valence shell is a happy element ☺ For two atoms to join together atoms must gain, lose or share electrons Elements with full valence shells do not easily gain or lose electrons  Stability Atoms want to gain stability Atoms will try to gain or lose electrons to have a full valence shell Metals try to lose electrons Non-Metals try to gain electrons Shape of Orbitals  Atomic Orbital S Orbital (sharp) – spherical cloud that become less dense as the distance from the nucleus increases  Atomic Orbital P Orbital (Principal) – dumbbell shaped cloud having two lobes on opposite side  Atomic Orbital D Orbital (Diffused) – four leaf clover shaped cloud as an hour and as a ring  Atomic Orbital F Orbital (fundamental) – difficult to represent and too complex Electron Configuration s=2 p=6 d = 10 f = 14  Pauli’s Exclusion Principle No more than two electron in an atom can occupy an orbital  Hund’s Rule One electron must enter first in each orbital, then second electron will be added  Aufbau Principle Electron fill first the orbital of the lowest energy until any added electron