CHEM 150 1nd Edition Lecture 21Outline of Last Lecture • To understand the quantum-mechanical model of an atom, we have to know aboutelectromagnetic radiation.• Section 7.2: Light behaves as a wave. It has a frequency (v) and a wavelength (λ) that are related by its speed. It refracts and diffracts• It undergoes constructive and destructive interference. V.λ = Cc=2.99792458x10^8m/s• Section 7.4: But light also behaves like a particle. The photoelectron effect (pp 319-321), in particular, was best explained if light consisted of small “packets” of energy (photons). The energy of a photon is related to its frequency.E= v . h h= 6.62606931x10^-34J.sOutline of Current Lecture • The H atom is one proton and one electron.• The energy of an orbital is determined solely by n.• All orbitals in a shell have the same energy.Current Lecture-An electron will preferentially occupy the lowest energy orbital available. The single electron in a hydrogen atom occupies the orbital with n=1, l=0, m=0 (the 1s orbital)-The lowest energy state for an atom, ion, or molecule, is to have all the electrons in the lowest energy orbitals possible. This is called the ground state.-Any other configuration of the electrons would be an excited state.-ground state electron configuration for H:H 1s^1-ground state orbital diagram for H:H 1-Write an electron configuration for an excited state of H:1s 2s-In the helium atom, a second electron also occupies the 1s orbital. Pauli exclusion principle: two electrons can occupy the same orbital if they have oppositespins.-This requires a fourth quantum number: m , the spin quantum number ms can have values of +½ and -½.-No two electrons in an atom can have the same set of four quantum numbers.• In helium:electron “A” n = 1, l = 0, m = 0, m = ½ electron “B” n = 1, l = 0, m = 0, m = -½ -The presence of more than one electron also affects the energy levels of the orbitals: Theenergy is now dependant upon the values of both n and l. (shell and subshell).Q: Write the full electron configuration for the ground state of:SiliconSi 1s^1 2S^2 2P^6 3S^2 3P^2ManganeseMn 1S^2 2S^2 2P^6 3S^2 3P^6 4S^2 3d^5Q: Draw orbital diagrams for the ground state of:carbon1s 2s 2piron[Ar] 2s 3d Q: What are the quantum numbers that specify the highest energy electrons in Si, Mn, C, and Fe?Si n=3 , l=1 , me= -1Mn n=3 , l=2, me= -2C n=2 , l=1, me=
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