Chem 121 1st Edition Lecture 7 Outline of Last Lecture I. The Mole (chapter 2)II. Molar Mass (chapter 2)III. Wave Nature of Light (chapter 3)IV. Electromagnetic Spectrum (chapter 3)Outline of Current Lecture V. The Nature of MatterVI. Atomic Spectrum of HydrogenVII. The Bohr Model of HydrogenVIII. The Wave Nature of MatterIX. Quantum Mechanics and the AtomX. Atomic OrbitalsXI. Quantum OrbitalsCurrent LectureThe Nature of Matter- Photoelectric Effect: Metal dislodge electrons upon EM radiation- “Threshold” frequency: Frequency that electron starts emittingo No electrons release no matter how bright the light iso Electrons always release no matter how dim the light iso Always a “threshold” frequency- KE: the higher the frequency, the greater speed of electrons emittedo Directly proportionate- Electromagnetic wave as particles (photoelectric effect)o Albert Einstein (1905-1911)o EM wave absorbed as packets of particleso Energy of EM wave: the higher the frequency, the shorter the wavelength,the higher the energyo Particles of EM wave- Proved by R.A. Millikan (1915)- Wave- particle duality of waveo Photon (particle): the smallest possible amount of EM energy o Has a discrete, fixed energyo Each photon has its own energy determined by the frequencyThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Atomic Spectrum of Hydrogen- Continuous Spectrum: Different colors blend into one another without any breaks- Line Spectrum (Discontinuous spectrum): o Emission: black background, different colored lineso Absorption: continuous spectrum, black/dim colored lineso Elemental fingerprint: every element has unique atomic spectrumThe Bohr Model of Hydrogen- Postulationso Electrons in Hydrogen atom cycling nucleus only in set of orbitso Orbits: concentric circles with fixed radiio Each orbit is associated with a definite energy level (state) 1st orbit: ground state (lowest); rest orbits: excited stateso Electrons do not radiate energy while in an orbit (found to be not true) Will not collide with nucleuso Electrons move from one orbit to another Change in energy is absorbed or emitted as a photon- Energy of Orbito En= (-2.18x10-18 J) (Z2 / n2) Z: atomic number=number of protons n: a set of numberso The lower the n; smaller the orbits, the closer electrons are to nucleus, the lower the energy stateo Energy exchange when electrons change orbit Excitation: electrons changes from the inner to the outer orbit by absorption E Relaxation: electrons change from outer to inner orbit by emitting hν The Wave Nature of Matter- Electrons behaves as wave (Louis de Broglie 1924)o An electron confined in an orbit: λ= h ÷ mv **o Prove: Electron diffraction (Davisson & Germer, 1927)o Electron cannot be confined in an orbit- Heinsenberg Uncertainty Principleo “The position and the velocity of an electron cannot be measured simultaneously beyond a certain level of precision” Only the region of an electron can be found Statistical probability maps can be used to show the location of an electron We can describe electrons in weightQuantum Mechanics and the Atom- The Schrodinger (wave) equationo H (x,y,z) = E (x,y,z)o  (x,y,z) - Wave function of electrons No direct physical meanings depicting electrons Different  (x,y,z) results in different E with definite valueso E: total energy of electrons associated with  (x,y,z)o Electrons depicted as a waveAtomic Orbitals- Wave function of electronso 2 (x,y,z)- atomic orbital (electron density and cloud)o The greater the density, the higher the probability in finding the electronswithin the volumeo Electron density will decrease as r increases but will never reach zeroo Characterized by 3 parameters calls quantum numbers n,l,mlo Orbital shape: A region of space where the electron can be found 95% of the time**Quantum Numbers**Biggest topic in chapter 3!!!!- Quantum numbers of an atomic orbital: any atomic orbital is specified by three quantum numberso n ( principle quantum number) : 1,2,3  infinity has no limit Determines size of orbital- distance from nucleus Determines shells in energy: same n, same shell- The higher the n, the higher the energy levelo l (angular momentum quantum number) : 0,1,2, (n-1)  has a limit, can never be larger than n Determined by n l<n (always start at zero) Determines shape of the orbitals Determines subshells in energy Total number of possible values of l=n ***Value of l 0 1 2 3 4Letter useds p d f gMUST MEMORIZE!- For n, there are always total n different values of l, starting with 0, … to