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LT1: Electron Arrangement (Ch. 5) How do fireworks work? Rutherford’s Model of the Atom Contributions Problems • Nucleus: Explains where positive protons and where the mass of the atom is found • Doesn’t explain electron arrangement or reactivity/properties of atoms • Electron Arrangement: electrons are outside the nucleus flying in empty space Characteristics of Waves Electromagnetic Radiation What is the relationship between wavelength and frequency of EM waves? How is Energy related? What does amplitude tell you about the wave? Why did the wave model of light need a revision? It didn’t explain why metals emit electrons when struck by certain types of light. It didn’t explain why only certain colors are emitted from heated objects. Planck and Quantum Matter can only gain a CERTAIN AMOUNT OF ENERGY= QUANTUM The colors emitted from an object when heated is directly related to the Quantum. Is light a wave or a particle? Why do we see colors from signs? neon What do you think the color depends on? Why do some atoms emit green and others emit red? Explanation--- remember ROYGBIV • Atoms are struck by Energy (light, flame, electricity). • The electrons are excited out of ground state to excited state where they are unstable. • As electrons fall back to ground state they give off the energy they absorbed as LIGHT. • The color depends on the quantum absorbed. • Higher quantum= BIV • Lower quantum= ROY Atomic emission spectrum= set of frequencies an atom gives offfingerprint for an atom Bohr’s Model Contributions • ENERGY LEVELS: • Electrons move in circular patterns around the nucleus like planets around the sun. • Closer to the nucleus= lower energy • Further from nucleus= higher energy • QUANTUM NUMBER: • n=1 closest to nucleus • Movement from n= 2 to n=1 results in a photon Visual Problems with Bohr Model • Doesn’t explain electron movement within Energy Levels correctly ▫ Electrons DO NOT orbit like planets around the sun • Only works for Hydrogen Accepted theory today: Quantum Mechanical Model of the Atom http://www.youtube.com/watch?v=-YYBCNQnYNM • Electrons are treated like waves • Electrons have certain ENERGY VALUES which dictate their distance from the nucleus ▫ Lower energy ___________ the nucleus ▫ Higher energy __________ the nucleus • DOES NOT explain electron path as “orbiting like planets around the sun” De Broglie and the Quantum Mechanical Model • Wave-like motion of electrons: all moving particles have wave-like motion that restricts how much energy the electrons can absorb and emit (QUANTUM) Schrodinger and the Quantum Mechanical Model • Atomic Orbitals: 3D space electrons are likely to be found ▫ SHAPES electron fly in Quantum Mechanical Model continued • Principal Quantum Number (n)= #’s assigned that correlates with: ▫ ▫ ▫ ▫ Size Speed of electron Distance from the nucleus Amount of energy electron has • COLOR AND LABEL A PERIODIC TABLE Atomic Orbitals Quantum Mechanical Model cont. • Principle Energy Level= correlates with the distance from the nucleus and amount of energy electron has. • Energy sublevels= the number of orbitals in each energy level Type of sublevel Shape # of orbitals (configurations) Max # of electrons s Sphere 1 2 p Dumbbell 3 6 d Clover 5 10 f Complex 7 14 Can you fill in the rest by looking at a Periodic table? Energy level or Principal Quantum Number 1 2 3 4 5 6 7 Sublevels Max # of electr ons 1s 2s, 2p 3s, 3p, 3d 2 8 18 Heisenberg Uncertainty Principle Electron ConfigurationMain Idea: A set of three rules can be used to determine electron arrangement in an atom. Aufbau Electrons occupy lowest energy level first. principle Pauli Exclusion Principle Electron have opposite spins if they are in the same orbital. Hund’s Rule Electrons occupy each orbital before pairing. Practice • Electron configuration of Sodium: • Orbital Notation of Sodium: • Noble Gas Configuration of Sodium: Exceptions to the Rules • Many transition metals don’t follow the rules • Copper and Chromium are common examples