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## CHAPTER 8 Atomic Electron Configurations and Chemical Periodicity

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**CHAPTER 8**Atomic Electron Configurations and Chemical Periodicity Road Map - Lesson 22Recap of Ch 7 problemsArea of Focus:Chapter 8The Exclusion Principle – introduction of the 4th q.n.Electron Spin Subshell filling orderAtomic electron configuration**Equations**• speed of light = wavelength x frequency c = λ X = 3.00 x 108 m/s • E = nh = nh(c/) n= positive integer Planck’s constant(h) = 6.626 x 10–34 J s • Eatom = Eemitted (or absorbed) radiation = nh • Rydberg equation = R • n2 > n1 • R = 1.096776 x 107 m-1 • ΔE = Efinal – Einitial = –2.18 x 10–18 J • Ephoton = Estate A – Estate B = hν**Practice Problem 22-1**• According to the quantum mechanical treatment of the hydrogen atom, which set of quantum numbers is not allowed? A) n = 3, ℓ = 2, mℓ = 0 B) n = 3, ℓ = 0, mℓ = 0 C) n = 3, ℓ = 1, mℓ = 1 D) n = 3, ℓ = 1, mℓ = -1 E) n = 3, ℓ = 1, mℓ = 2**Practice Problem 22-1 Answer**• According to the quantum mechanical treatment of the hydrogen atom, which set of quantum numbers is not allowed? A) n = 3, ℓ = 2, mℓ = 0 B) n = 3, ℓ = 0, mℓ = 0 C) n = 3, ℓ = 1, mℓ = 1 D) n = 3, ℓ = 1, mℓ = -1 E) n = 3, ℓ = 1, mℓ = 2**Practice Problem 22-2**• For an excited hydrogen atom with the quantum number n equal to 9, which of the following statements is true? A) The energy of the atom is less than the energy for the state in which n is equal to 8. B) If ℓ = 0, there are nine possible values for the magnetic quantum number mℓ. C) The smallest value of the magnetic quantum number mℓ is -9. D) The electron must be in one of the p orbitals. E) The angular momentum quantum number ℓ can have any of the values 0, 1, 2, 3, 4, 5, 6, 7, 8.**Practice Problem 22-2 Answer**• For an excited hydrogen atom with the quantum number n equal to 9, which of the following statements is true? A) The energy of the atom is less than the energy for the state in which n is equal to 8. B) If ℓ = 0, there are nine possible values for the magnetic quantum number mℓ. C) The smallest value of the magnetic quantum number mℓ is -9. D) The electron must be in one of the p orbitals. E) The angular momentum quantum number ℓ can have any of the values 0, 1, 2, 3, 4, 5, 6, 7, 8.**Practice Problem 22-3**• According to the quantum-mechanical model, how many orbitals in a given atom have n = 3? A) 4 B) 7 C) 9 D) 10 E) 18**Practice Problem 22-3 Answer**• According to the quantum-mechanical model, how many orbitals in a given atom have n = 3? A) 4 B) 7 C) 9 D) 10 E) 18**Chapter 8**• The Exclusion Principle – introduction of the 4th q.n. • Hund’s rule • Electron Spin • Subshell filling order • Atomic electron configuration**Chapter 8**• Pauli Exclusion Principle - No two electrons in the same atom can have the same set of 4 quantum numbers. • each electron has a unique address. • HUND’S RULE - When placing electrons in a set of orbitals having the same energy, we place them singly as long as possible. • aufbau principleis the building up process that results in ground-state electron configurations**Electron Configurations and the Periodic Table**Active Figure 8.7**spdf notation**for H, atomic number = 1 1 no. of s 1 electrons value of l value of n Writing Atomic Electron Configurations Two ways of writing configs. • the spdf notation. • the orbital box notation. One electron has n = 1, l = 0, ml = 0, ms = + 1/2 Other electron has n = 1, l = 0, ml = 0, ms = - 1/2**Yellow P**Red P Phosphorus Group 5A Atomic number = 15 1s2 2s2 2p6 3s2 3p3 [Ne] 3s2 3p3 All Group 5A elements have [core ] ns2 np3 configurations where n is the period number.**General Periodic Trends**• Atomic and ionic size • # electrons • # shells – Larger orbitals, -electrons held less tightly • Ionization energy • Electron affinity • energy involved when an atom gains an electron to form an anion. • Effective nuclear charge • When higher: Electrons held more tightly**Effective Nuclear Charge, Z***• Z* is the nuclear charge experienced by the outermost electrons. • Z* increases across a period owing to incomplete shielding by inner electrons. • The 2s electron PENETRATES the region occupied by the 1s electron. • 2s electron experiences a higher positive charge than expected. • Estimate Z* by --> [ Z - (# inner electrons) ] • Charge felt by 2s e- in Li Z* = 3 - 2 = 1 • Be Z* = 4 - 2 = 2 • B Z* = 5 - 2 = 3 and so on!**Ion Configurations**To form cations, always remove electrons of highest n value first! P [Ne] 3s2 3p3 - 3e- ---> P3+ [Ne] 3s2 3p0**+**+ Li , 78 pm 2e and 3 p Ion Sizes • CATIONS are SMALLER than the atoms from which they come. • The electron/proton attraction has gone UP and so size DECREASES. Forming a cation. Li,152 pm 3e and 3p**-**- F, 71 pm F , 133 pm 9e and 9p 10 e and 9 p Ion Sizes • ANIONS are LARGER than the atoms from which they come. • The electron/proton attraction has gone DOWN and so size INCREASES. • Trends in ion sizes are the same as atom sizes. Forming an anion.**Trends in Ion Sizes**Active Figure 8.15**Ionization Energy**IE = energy required to remove an electron from an atom in the gas phase. Mg (g) + 738 kJ ---> Mg+ (g) + e- Mg+ (g) + 1451 kJ ---> Mg2+ (g) + e- Mg+ has 12 protons and only 11 electrons. Therefore, IE for Mg+ > Mg