Presentation on theme: "C. Johannesson Ch. 4 - Electrons in Atoms. Section 1 The Development of a New Atomic Model Objectives Explain the mathematical relationship among the."— Presentation transcript:
Section 1 The Development of a New Atomic Model Objectives Explain the mathematical relationship among the speed, wavelength, and frequency of electromagnetic radiation. Discuss the dual wave-particle nature of light. Discuss the significance of the photoelectric effect and the line-emission spectrum of hydrogen to the development of the atomic model. Describe the Bohr model of the hydrogen atom.
C. Johannesson Electromagnetic Spectrum LOWENERGYLOWENERGY HIGHENERGYHIGHENERGY yIncludes all forms of electromagnetic radiation (energy that exhibits wavelike behavior as it travels through space)
Click below to watch the Visual Concept. Visual Concept Electromagnetic Spectrum
Waves zWavelength ( ) - length of one complete wave zFrequency ( ) - # of waves that pass a point during a certain time period yhertz (Hz) = 1/s zAmplitude (A) - distance from the origin to the trough or crest
C. Johannesson Waves A greater amplitude (intensity) greater frequency (color) crest origin trough A
on EM Spectrum LOWENERGYLOWENERGY HIGHENERGYHIGHENERGY ROYG.BIV redorangeyellowgreenblueindigoviolet LONG WAVELENGTHLONG WAVELENGTH
EM Spectrum zFrequency & wavelength are inversely proportional c = c:speed of light 3.00 10 8 m/s (in a vacuum) :wavelength (m, nm, etc.) :frequency (Hz)
EM Spectrum GIVEN: = ? = 434 nm = 4.34 10 -7 m c = 3.00 10 8 m/s WORK : = c = 3.00 10 8 m/s 4.34 10 -7 m = 6.91 10 14 Hz zEX: Find the frequency of a photon with a wavelength of 434 nm.
Click below to watch the Visual Concept. Visual Concept Energy of a Photon
Electrons as Waves EVIDENCE: DIFFRACTION PATTERNS ELECTRONS VISIBLE LIGHT Electrons, like light waves, can be bent, or diffracted. Diffraction refers to the bending of a wave as it passes by the edge of an object or through a small opening
Bohr Model of the Hydrogen Atom Niels Bohr proposed a hydrogen-atom model that linked the atom’s electron to photon emission. According to the model, the electron can circle the nucleus only in allowed paths, or orbits. Electrons are allowed to exist in any one of a number of energy levels (lowest energy state is closest to the nucleus) Only worked for Hydrogen (1 electron)
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zPlanck (1900) yObserved - emission of light from hot objects yConcluded - energy is emitted in small, specific amounts (quanta) not continuously as expected by energy in the form of waves yQuantum - minimum amount of energy that can be lost or gained by an atom
Quantum Theory zPlanck (1900) vs. Classical TheoryQuantum Theory
zEinstein (1905) yObserved - photoelectric effect- emission of electrons from a metal when light shines on the metal
zEinstein (1905) yConcluded - light has properties of both waves and particles “wave-particle duality” yPhoton - particle of light that carries a quantum of energy
Click below to watch the Visual Concept. Visual Concept Quantization of Energy
Line-Emission Spectrum zEach element has a unique bright-line emission spectrum. yHydrogen always produced same line- emission spectrum so releases (emission) energy of only certain values y“Atomic Fingerprint” Helium
Line-Emission Spectrum Cont… ground state- lowest energy state of an atom excited state- state in which an atom has a higher potential energy than its ground state ENERGY IN PHOTON OUT yLine –emission spectrum is caused by energy released when electrons “jump from higher energy to lower energy
C. Johannesson Electrons as Waves zLouis de Broglie (1924) yApplied wave-particle theory to e - ye - exhibit wave properties as well as particle QUANTIZED WAVELENGTHS
Quantum Mechanics zHeisenberg Uncertainty Principle yImpossible to know both the velocity and position of an electron (small particle) at the same time zQuantum theory describes mathematically the wave properties of electrons and other very small particles.
Quantum Mechanics Electrons do not travel around the nucleus in neat orbits, as Bohr had postulated. Instead, they exist in certain regions called orbitals. Orbital (“electron cloud”) yRegion in space where there is 90% probability of finding an e - three- dimensional space Orbital
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Electron Configuration zArrangement of electrons in an atom zAtoms of different elements have different numbers of e-, a distinct electron configuration exists for atoms of each element ze- in atoms tend to assume arrangements that have lowest possible energies (ground-state)
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General Rules zPauli Exclusion Principle yEach orbital can hold TWO electrons with opposite spins.
General Rules zAufbau Principle yElectrons fill the lowest energy orbitals first. y“Lazy Tenant Rule” yEnergies of sub-levels begin to overlap x4s is lower in energy than 3d
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RIGHT WRONG General Rules zHund’s Rule yWithin a sublevel, place one e - per orbital before pairing them. ySeparating unpaired electrons into as many orbitals as possible minimizes the repulsion between electrons
O 8e - zOrbital Diagram zElectron Configuration 1s 2 2s 2 2p 4 Notation 1s 2s 2p
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