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Arrangement of Electrons in Atoms Chapter 4

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The New Atomic Model Investigations relationship between light and atoms electrons How are electrons arranged? Why dont they fall into the nucleus?

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Light a wave or particle? Wave Description: Electromagnetic Radiation: energy that acts like a wave in space All forms create Electromagnetic Spectrum

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Electromagnetic Spectrum

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All forms move at speed of light, c, 3.00x10 8 m/s Forms identified by: wavelength,, the distance b/ corresponding points on adjacent waves. Units: nm, cm, or m Frequency,, # of waves that pass a given point in a specific time, 1 sec. Unit: 1/s = Hertz, Hz

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Wavelength and Frequency

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c = Inverse proportion equation!! speed of light, m/s wavelength, m Frequency, 1/s

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Calculation Calculate the wavelength of a radio wave with a frequency of x 10 6 s -1 Determine the frequency of light whose wavelength is nm.

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Particle Nature of Light Photoelectric Effect: emission of electrons from a metal when light shines on the metal

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Photoelectric Effect Light had to be certain frequency to knock e - loose Wave theory any frequency should work (just might take a while) Light must also be a particle! Max Planck(1900) explanation: objects emit energy in small packets called quanta Video - 16

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Max Planck Quantum of energy is the smallest amount of energy that can be lost or gained by an atom E = h Energy of quantum, in joules, J Plancks constant, 6.626x Js Frequency, s -1

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Energy Calculation What is the energy of green light, with a wavelength of 500. nm?

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Albert Einstein Light is both wave and particle! Particle of light = photon, having zero mass and a quantum of energy Photons hit metal and knock e - out, but photon has to have enough energy

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H-atom Emission Spectrum Pass a current through gas at low pressure it excites the atoms Ground state: lowest energy state of an atom Excited state: atom has higher potential energy than it has in ground state

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H – Atom Spectrum When atom jumps from excited state to ground state it gives off energy LIGHT! E photon = E 2 – E 1 = hv E2E2 E1E1

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Bohr Model of H-atom

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H-atom Line Emission Spectrum

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Element Emission Spectras Helium – 23 lines Neon – 75 lines Argon lines Xenon – 139 lines Mercury – 40 lines

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H-atom Line Emission Spectrum More lines in UV (Lyman series) and IR(Paschen series) Why did H-atom only emit certain colors of light? Explanation led to new atomic theory Quantum Theory

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Bohr Model of H-atom 1913 – Niels Bohr e - circles nucleus in certain paths, orbits or atomic energy levels e - is higher in energy the farther away from nucleus e - cannot be between orbits Video - 23

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Bohr Model of H-atom

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From wavelengths of emission spectrum Bohr calculated energy levels of H-atom Model worked ONLY for H-atom

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Quantum Model of Atom Can e - behave as a wave? Yes! To find e - use a photon, but photon will knock the e - off course Heisenberg Uncertainty Principle: impossible to determine position and velocity of a particle at the same time.

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Schrödinger Wave Equation 1926 – developed equation and only e - waves of certain frequencies were solutions Quantization of e - probability of finding e - in atom No neat orbits probability clouds or orbitals

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Electron Configurations

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Atomic Orbitals Def: 3-D region around nucleus that indicates the probable location of an electron Energy levels or shells: Numbered 1-7 Smaller number = closer to nucleus, lower energy

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Sublevels Each shell has sublevels s 1 – s orbital p 3 – p orbitals d 5 – d orbitals f 7 – f orbitals

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Shells and Sublevels Shells and sublevels together: 1s 2s, 2p 3s, 3p, 3d 4s, 4p, 4d, 4f, etc. s is the lowest energy and f is the highest

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Orbitals Each orbital in a sublevel can hold a maximum of 2 e - 1 – s 2 e - max. 3 – p orbitals 6 e - max. 5 – d orbitals 10 e - max. 7 – f orbitals 14 e - max.

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Electron Configurations Arrangement of e - in atom Orbital Notation: H has 1e - Rules: 1. Aufbau Principle: electron occupies lowest energy level that can receive it

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Electron Configurations 2. Pauli Exclusion Principle: no two e - in an sublevel orbital can have the same spin 3. Hunds Rule: orbitals of equal energy are occupied by one e - before pairing up e -. All single occupied orbitals must have same spin. He – 2e -

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Energy of sublevels

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Electron Configurations N S Ti I

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Electron Configuration Notation B Ni Hg

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Noble Gas Notation Use noble gas from previous row Al Pb

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Special Cases d sublevel more stable with half-filled or completely filled sublevel Cr Cu

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