Chapter 5 Electrons in Atoms Chemistry Section 5.1 Light and Quantized Energy At this point in...
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Transcript of Chapter 5 Electrons in Atoms Chemistry Section 5.1 Light and Quantized Energy At this point in...
![Page 1: Chapter 5 Electrons in Atoms Chemistry Section 5.1 Light and Quantized Energy At this point in history, we are in the early 1900’s. Electrons were the.](https://reader035.fdocuments.us/reader035/viewer/2022062805/5697bfae1a28abf838c9cb40/html5/thumbnails/1.jpg)
Chapter 5
Electrons in AtomsChemistry
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Section 5.1 Light and Quantized Energy
• At this point in history, we are in the early 1900’s. Electrons were the 1st subatomic particle to be discovered.
• Chemists have a Rutherford Model of the atom. There is a small, dense, positively charged center of the atom called a nucleus. Electrons move around outside the nucleus.
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The Atom and Unanswered Questions
• In Rutherford's model, the atom’s mass is concentrated in the nucleus and electrons move around it.
• The model doesn’t explain how the electrons were arranged around the nucleus.
• The model doesn’t explain why negatively charged electrons aren’t pulled into the positively charged nucleus.
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• In the early 1900s, scientists observed certain elements emitted visible light when heated in a flame.
• Analysis of the emitted light revealed that an element’s chemical behavior is related to the arrangement of the electrons in its atoms.
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The Wave Nature of Light
• Visible light is a type of electromagnetic radiation, a form of energy that exhibits wave-like behavior as it travels through space.
• All waves can be described by several characteristics.
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• The wavelength (λ) is the shortest distance between equivalent points on a wave.
• The frequency (ν) is the number of waves that pass a given point per second.
• The amplitude is the wave’s height from the origin to a crest.
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What relationship do you see between λ, v, and c?
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• The speed of light (3.00 108 m/s) is the product of it’s wavelength and frequency.
c = λν
What relationship do you see between λ and ν?
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• Sunlight, or visible light, contains a continuous range of wavelengths and frequencies.
• A prism separates sunlight into a continuous spectrum of colors – pg. 138.
• The separation of white light by a prism• The electromagnetic spectrum includes all
forms of electromagnetic radiation – pg. 139.
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The Electromagnetic Spectrum
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Visible Light …
Note the trends: Blue light has shorter λ, higher v, andmore energy. Red light has longer λ, lower v, and lessenergy.
Brain Pop - The EM Spectrum
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• The wave model of light cannot explain all of light’s characteristics.
• An example is the photoelectric effect , when electrons are emitted from a metal’s surface when light of a certain frequency shines on it (how solar calculators work).
• Photoelectric Effect Simulation
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• Albert Einstein proposed in 1905 that light has a dual nature.
• Einstein suggested a beam of light has wavelike and particlelike properties.
• A photon is a particle of electromagnetic radiation with no mass that carries a quantum of energy.
Ephoton = h
Ephoton represents energy, h is Planck's constant (6.626 x 10-34 J-s), & represents frequency.
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Atomic Emission Spectra • Light in a neon sign is produced when
electricity is passed through a tube filled with neon gas and excites the neon atoms.
• The excited atoms emit light to release energy.
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Emission Spectrum for Hydrogen
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• The atomic emission spectrum of an element is the set of frequencies of the electromagnetic waves emitted by the atoms of the element.
• Each element’s atomic emission spectrum is unique – they have their own fingerprints!
Absorption and Emission Spectra's
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Section 5.2 Quantum Theory and the Atom
Bohr's Model of the Atom…• Bohr suggested that an
electron moves around the nucleus only in certain allowed circular orbits - Planetary Atomic Model.
• The lowest allowable energy state of an atom is called its ground state.
• When an atom gains energy, it is in an excited state.
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Planetary Atomic Model
Bohr Model
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• Bohr assigned a quantum number for each principal energy level.
• The highest quantum number can be found by the period the element is in on the Periodic Table.
• He tried to predict the spectral lines for elements following Hydrogen, but was not successful.
• The behavior of electrons is still not fully understood, but it is known they do not move around the nucleus in circular orbits.
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Big Discoveries…• Louis de Broglie
hypothesized that particles, including electrons, could also have wavelike behaviors.
• Werner Heisenberg showed it is impossible to take any measurement of an object without disturbing it.
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• The Heisenberg uncertainty principle states that it is fundamentally impossible to know precisely both the velocity and position of a particle at the same time.
• The only quantity that can be known is the probability for an electron to occupy a certain region around the nucleus.
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Our Current Atomic Theory…
• Erwin Schrödinger treated electrons as waves in a model called the quantum mechanical model of the atom. Most people call this the Electron Cloud Model.
• This model applied to all elements!!!
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• The Electron Cloud is a 3-D arrangement of electrons around the nucleus.
• Within the cloud, electrons are arranged by energy level, sublevel, and orbital shape.
• When combined, a spherical shape is the result.
• There is an attraction between the positively charged nucleus and the negatively charged electrons in the electron cloud.
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Orbital Shapes…
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Section 5.3 Electron Configuration
Valence Electrons• Valence electrons are defined as electrons
in the atom’s outermost orbitals—those associated with the atom’s highest principal energy level.
• An element’s valence electrons determine the chemical properties of the element.
• The number of valence electrons can be found using its group number on the periodic table.
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• Electron-dot structure consists of the element’s symbol representing the nucleus and inner electrons, surrounded by dots representing the element’s valence electrons.