Chapter 2 Slides

Chapter 2 Slides - Chapter 2 Lecture on 01-10-08 Revised...

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1 Chapter 2 - Chapter 2 • Revised slides 6,7,14, and added new slides 10,13 after lecture on 01-10-08 Lecture on 01-10-08
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2 Chapter 2 - ISSUES ADDRESSED. .. • What promotes bonding? • What types of bonds are there? • What properties are controlled by bonding? CHAPTER 2: BONDING AND PROPERTIES
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3 Chapter 2 - Fundamental concepts • Atomic number Z – the number of protons or the number of electrons in the neutral atom – C = 12, Fe = 26 • Mass of proton – 1.67 x 10 -27 kg • Mass of electron – 9.11 x 10 -31 kg • Atomic mass number or atomic weight for an element A = Z + N – N is the weighted average number of neutrons in the element – Generally A is a non-integer number because elements have several isotopes with different numbers of neutrons (U 235 , U 238 ) – Isotopes of the same element contain the same number of protons and electrons but the neutron count varies • Atomic mass varies because N varies • Chemical properties do not change because Z is constant – At wt. of Fe as found in nature is 55.85 g/mol – 1 mol of any element or molecule contains Avogadro’s number of atoms or molecules – 6.023 x 10 23
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4 Chapter 2 - Electrons in Atoms - 1 The original Bohr model needs modifying by the wave-particle duality picture of Quantum Mechanics – now electron position is a probability function Bohr model: atoms are mostly empty space Electrons can only occupy individual energy states – outer levels are more easily perturbed Bohr view quantum view
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5 Chapter 2 - Electrons in atoms - 2 At left the original Bohr view – fixed position while at right is the correct quantum modification with a probability of finding the electron orbit quantum classical
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6 Chapter 2 - Quantum Numbers Electron spin +1/2, -1/2 m s Spatial orientation of the electron clouds -l to +l s = 0; p = -1,0,1 d = -2,-1,0,1,2 f = -3,-2,-1,0,1,2,3 m l Shape of the electron cloud s – omni-directional p, d, f directional 0,1,2,3… to n-1 K: l = 0 (s) L: l = 0,1 (s,p) M: l = 0,1,2 (s,p,d) Sub shell l Energy level 1, 2, 3, 4… K, L, M, N… Principal n Property Values Quantum number name
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7 Chapter 2 - Quantum Numbers - m l Wikipedia M L K N P O Q
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8 Chapter 2 - Energy levels for shells As n rises, so does the energy As the wave function (electron cloud shape) of the electrons becomes less symmetric, so too does the energy rise At larger n levels, for example 5s the energy can be lower than that of 4d or 4f, leading to anomalies in filling – i.e. 5S fills before 4f
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Chapter 2 Slides - Chapter 2 Lecture on 01-10-08 Revised...

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