2010-01-20 Chapter 02 Atomic Structure and Bonding

2010-01-20 Chapter 02 Atomic Structure and Bonding -...

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ISSUES TO ADDRESS... What promotes atomic bonding? What types of bonds are there? What properties are inferred from bonding? 1 CHAPTER 2: Atomic Structure & Interatomic Bonding Why study Atomic Structure & Interatomic Bonding? Type of bond allows us to explain a material’s properties. e.g. Metallic bonded materials are good conductors of heat and electricity due to free electrons. Ionically and covalently bonded materials are typically insulative to heat and electricity e.g.ceramics.
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BACKGROUND An Atom is the basic unit of matter. Atom has a Nucleus composed of Protons (positively charged, +) & Neutrons (neutral). Mass proton = Mass neutron = 1.67 x 10 -27 kg Number of protons = Z = Atomic Number, determines the chemical element Number of Neutrons = N, determines the isotope Sum of masses of protons and neutrons = A = Atomic Mass Atomic Weight = Weighted Average of Atomic Masses, in g/mol The Nucleus of an Atom is encircled by moving Electrons (negatively charged, -) Mass = 9.11 x 10 -31 kg <<< protons and neutrons. Charge magnitude for an electron = -1.60 x 10 -19 C Charge magnitude for a proton = +1.60 x 10 -19 C Electrons strongly influence the magnetic properties of atoms. Number of electrons = Number of protons for electrically neutral or, complete atom. 1 mole of matter = 6.023 x 10 23 atoms or molecules = Avogadro’s number
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Chapter 2- Nucleus: Z = number of protons 2 orbital electrons: n = principal quantum number n=3 2 1 N = number of neutrons Adapted from Fig. 2.1, Callister 6e. BOHR ATOMIC MODEL In this model, electrons are assumed as particles revolving around nucleus in discrete orbitals.
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Wave-mechanical model considers electron to exhibit both wave- like and particle-like characteristics. Position of electron is described by probability distribution Electron in atom is characterized by Quantum Numbers . Shells: principal quantum no.(n = 1,2,3,4,.. or, K, L, M, N) Subshells: second quantum no.(s, p, d, and f) Energy states: third quantum no. Spin moment: fourth quantum no. WAVE-MECHANICAL ATOMIC MODEL Principal Quantum No Shell Subshell No. of Energy State No of Electrons Per Subshell Per Shell 1 K s 1 2 2 2 L s 1 2 8 p 3 6 3 M s 1 2 18 p 3 6 d 5 10 4 N s 1 2 32 p 3 6 d 5 10 f 7 14
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Shells s,p,d,f are subshells ELECTRON ENERGY STATES 1. For smaller quantum number energy is lower. 1s < 2s < 3s 2. Within each shell energies are: s < p < d < f 3. There may be overlap in energies in the adjacent shells. e.g. 3d > 4s Electrons tend to occupy lowest available energy state. Important
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Chapter 2- have discrete energy states or, levels. tend to occupy lowest available energy state. 3 Increasing energy n=1 n=2 n=3 n=4 1s 2s 3s 2p 3p 4s 4p 3d Electrons... Adapted from Fig. 2.5, Callister 6e. ELECTRON ENERGY STATES Electron can change energy to higher energy (by absorbing energy) or, lower energy (by emitting energy).
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