Chapter2

Chapter2 - 1 MSE 2090: Introduction to Materials Science...

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Unformatted text preview: 1 MSE 2090: Introduction to Materials Science Chapter 2, Bonding Review of Atomic Structure Electrons, protons, neutrons, quantum mechanics of atoms, electron states, the periodic Table Atomic Bonding in Solids Bonding energies and forces Primary Interatomic Bonding Ionic Covalent Metallic Secondary Bonding Three types of dipole-dipole bonds Molecules and molecular solids Chapter Outline Understanding of interatomic bonding is the first step towards understanding/explaining materials properties 2 MSE 2090: Introduction to Materials Science Chapter 2, Bonding Nature of Interatomic Bonding Why the individual atoms coalesce into larger structures and take on the characteristics and properties of many different materials? People were trying to answer this question for well over two millennia, since the time of the atomic hypothesis of Democritus, 440 B.C. * Roman poet Lucretius (95-55 B.C.) wrote in De Rerum Natura (On the Nature of Things): What seems to us the hardened and condensed Must be of atoms among themselves more hooked, Be held compacted deep within, as it were By branch-like atoms- of which sort the chief Are diamond stones, despisers of all blows, And stalwart flint and strength of solid iron John Dalton (1766-1844) found the evidence of those "hooks in his quantitative chemical measurements, making the foundation of modern atomic theory of matter. * the idea that everything is made of distinct atoms has been a subject of skeptical discussions as recently as the beginning of the twentieth century, before Einsteins observation of Brownian motion in 1905 and Max von Laues observation of the diffraction of X-rays by crystals in 1912 provided strong support for the atomistic theory. 3 MSE 2090: Introduction to Materials Science Chapter 2, Bonding Atoms = nucleus (protons and neutrons) + electrons Structure of atoms: Brief review Charges: Electrons and protons have negative and positive charges of the same magnitude, 1.6 10-19 Coulombs. Neutrons are electrically neutral. Masses: Protons and Neutrons have the same mass, 1.67 10-27 kg. Mass of an electron is much smaller, 9.11 10-31 kg and can be neglected in calculation of atomic mass. # protons gives chemical identification of the element # protons = atomic number (Z) # neutrons defines isotope number The atomic mass (A) = mass of protons + mass of neutrons The bonding mechanisms between atoms are closely related to the structure of the atoms themselves. 4 MSE 2090: Introduction to Materials Science Chapter 2, Bonding Atomic mass units. Atomic weight. The atomic mass unit (amu) is often used to express atomic weight. 1 amu is defined as 1/12 of the atomic mass of the most common isotope of carbon atom that has 6 protons (Z=6) and six neutrons (N=6)....
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Chapter2 - 1 MSE 2090: Introduction to Materials Science...

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