EGN3365-2a

EGN3365-2a - Chapter 2. Atomic structure and Interatomic...

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EGN3385 1 1 Chapter 2. Atomic structure and Interatomic Bonding •Atomic Structure •Electrons, protons and neutrons in atoms (Bohr and QM models) •The periodic table •Atomic Bonding •Bonding forces and energies •Primary interatomic bonds •Secondary bonding •Molecules 2 Why Study Atomic Structure and interatomic Bonding? • An extremely large number of microscopically small hairs on each of their toe pads • Weak forces of attraction (i.e., van der Waals forces) are established between hair molecules and molecules on the surface • Self-cleaning: dirt particles don’t stick to these toe pads • Synthetic self-cleaning adhesives??? Some of the important properties of solid materials depends on geometrical atomic arrangements and also the interactions that exist among constituent atoms or molecules.
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EGN3385 2 3 Atomic Structure fundamental concepts atom – electrons – 9.11 x 10 -31 kg protons neutrons atomic number Z = # of protons in nucleus of atom = # of electrons of neutral species atomic mass A atomic mass unit = amu = 1/12 mass of 12 C (A=12.00000 for 12 C) Isotopes? A tomic wt = wt of 6.023 x 10 23 molecules or atoms 1 amu/atom = 1g/mol } 1.67 x 10 -27 kg N Z A + nucleus 4 Electrons In Atoms- Bohr Atomic Model ¿½¼ÀÁ² Àµµ ¿ ¿Äº½´Ä Å»¼À ÆÁÇÈ ÉÈÊË Ì³³Áµ½´»Í´È ! Bohr atomic model: Electrons are assumed to revolve around the atomic nucleus in discrete orbitals , and the position of any particular electron is more or less well defined in terms of its orbital. ! Quantum-mechanical principle: the energies of electrons are quantized ---electrons are permitted to have only specific values of energy. Energy levels or states are separated by finite energies. ¼» Á½Â³ ´³´²½»¼¾µ¶ ¾ ¸ º»Á¾²ÁºÂ³ !±Â¾½±À ¾±À ´» ¾¸" É Ê Electron orbitals & quantized energy levels
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EGN3385 3 Electron Sir Joseph John Thomson (1856-1940) Nobel prize 1906 Thomson’s 2 nd Cathode ray experiment • In 1897, J.J.Thomson discovered “corpuscles”, small particles with a charge/mass ratio more than 1000 times
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EGN3365-2a - Chapter 2. Atomic structure and Interatomic...

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