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Chapter 5: Electrons In Atoms Bohr Model of the Atom Bohr proposed that an electron is found only in specific circular paths, or orbits, around the nucleus. Each orbit has a fixed energy The fixed energy an electron can have are called energy levels Energy and Electrons Electromagnetic Radiation Electromagnetic radiation consists of oscillating electric and magnetic fields that are perpendicular to each other. Electromagnetic radiation is a result of the motion of electrically charged particles (specifically electrons) Waves Electromagnetic radiation travels in waves Characteristics of waves Amplitude: height of wave Wavelength (): distance from crest to crest of waves Frequency (): number of wave cycles in a period of time (Hertz) Speed (c): all EM radiation travels at the speed of light when in a vacuum Waves Waves = c/ wavelength is inversely proportionate to frequency as wavelength increases; frequency decreases and vice versa E=h Energy is directly proportionate the frequency As frequency increases; energy increases Forms of Electromagnetic Radiation Radio waves Microwaves Infrared waves Visible (ROY-G-BIV) Ultraviolet X-Rays Gamma Rays EM Spectrum Spectrum of light Spectrum of light Sunlight is a combination of all frequencies of visible light When sunlight is passed through a prism, the different frequencies of light separate into a spectrum of colors. Atomic emission spectra When atoms absorb energy, electrons move into higher energy levels, and these electron lose energy by emitting light when they return to lower energy levels. Ordinary light is a mixture of all wavelengths, but light emitted by atoms consists of a mixture of only specific frequencies. These specific wavelengths are represented by a specific colors When the light is separated it gives distinct lines and creates an atomic emission spectrum of the element Wave/Particle Duality Louis DeBorglie Particles of matter behave like waves = h/p Wave/Particle Duality Arthur Compton Light behaves like a particle Photons can collide with electrons and knock them off their path because electrons are so small Wave/Particle Duality Therefore… light behave as both a particle and a wave Therefore… electrons behave as both a particle and a wave Heisenberg Uncertainty Principle It is impossible to know exactly both the velocity and position of an electron at the same time. Quantum Mechanical Model Heisenberg’s Uncertainty principle changes the modern atomic model Instead of electrons moving around the nucleus on paths, the electrons are like a cloud around the nucleus Similar to the propeller on a plane. Atomic Orbitals An atomic orbital is a region of space in which there is a high probability of finding an electron. Electron Configurations An Electron configuration is similar to a map of where each electron is likely located around the atom. The four sublevels and their orbitals!! s sublevel Number of Orbitals: 1 Capacity: 2 electrons p sublevel Number of Orbitals: 3 Capacity: 6 electrons d sublevel Number of Orbitals: 5 Capacity: 10 electrons f sublevel Number of Orbitals: 7 Capacity: 14 electrons 3 Rules of Electron Configurations Aufbau Principle Electrons occupy the orbitals of lowest energy first. 3 Rules of Electron Configurations Pauli Exclusion Principle Each orbital can hold no more than two electrons and must have opposite spins 3 Rules of Electron Configurations Hund’s Rule One electron must enter each orbital until all the orbitals contain one electron. Then the electrons can be paired.