Chapter_2 - The structure of atoms Chapter 2 Atomic...

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1 2.1 Atomic Structure ± The structure of atoms Chapter 2 Atomic Structure & Bonding Chapter 2 ME 201: Materials Science, Z. Hao 1 ± Atomic number and atomic mass ± Electronic structure of atoms 2.2 Atomic and Molecular Bonds ± Primary bonds ± Secondary Bonds The structure of atoms ATOM Basic Unit of an Element Diameter : 10 –10 m. Neutrally Charged Nucleus Diameter : 10 –14 m Electron Cloud Mass : 9 109 x 10 –28 g Chapter 2 ME 201: Materials Science, Z. Hao Accounts for almost all mass Positively Charged Mass : 9.109 x 10 Charge : -1.602 x 10 –19 C Accounts for all volume Proton Mass : 1.673 x 10 –24 g Charge : 1.602 x 10 –19 C Neutron Mass : 1.675 x 10 –24 g Neutrally Charged If neutrally charged Proton No. = Electron No. ± Atomic Number: ¾ Number of protons in the nucleus ¾ Unique to an element ¾ Identify an element Example: Hydrogen 1 Atomic Number and Periodic Table Chapter 2 ME 201: Materials Science, Z. Hao 3 Oxygen 6 ± Periodic Table (page 27) ¾ Atomic Number ¾ Element symbol ¾ Relative atomic mass Nucleus Protons ± Relative atomic mass of an element Mass of 6.203 x 10 23 ( Avagadro’s Number ) atoms (grams) Example: C: 12.01g, O: 16.00g (6.203 x 10 23 atoms=1mol atoms) ± Atomic mass unit (u) 1/12th of the mass of a carbon atom Atomic Mass (1) Chapter 2 ME 201: Materials Science, Z. Hao 4 Example: C: 12u, O: 16u, B:10.81u ± One gram-mole of an element Mass of the relative molar atomic mass (grams) Example: 1 gram-mole of aluminum (13): 1 gram-mole of N (7) mass: 26.98g, 6.203 x 10 23 atoms mass: 14.01g, 6.203 x 10 23 atoms Question: A 100 gram alloy of nickel and copper consists of 75 wt% Cu and 25 wt% Ni. What are percentage of Cu and Ni Atoms in this alloy? Solution: Given: 75g Cu (29) Atomic mass 63.54g/mol 25g Ni (28) Atomic mass 58.69g/mol Number of moles of Cu = Atomic Mass (2) - Example mol . g 1803 1 75 = Chapter 2 ME 201: Materials Science, Z. Hao 5 Number of moles of Cu = Number of moles of Ni = Atomic Percentage of Cu = Atomic Percentage of Ni = g/mol . 54 63 mol . g/mol . g 4260 0 69 58 25 = % 5 . 73 100 ) 4260 . 0 1803 . 1 ( 1803 . 1 = × + % 5 . 26 100 ) 4260 . 0 1803 . 1 ( 4260 . 0 = × + ± Definite energy levels ± Transitions ± Quantum numbers Electron Structure of Atoms Chapter 2 ME 201: Materials Science, Z. Hao 6 ± Electron configuration ± Chemical activity
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2 ± Certain orbitals within which an electron is restricted to rotate ± Bohr Equation(hydrogen): Potential energy at Energy level n Definite Energy Levels (1) eV h n me E n 2 2 2 4 2 6 . 13 2 = = π n=1 Chapter 2 ME 201: Materials Science, Z. Hao 7 m: electron mass = 9.109 x 10 –28 g e: electron charge= -1.602 x 10 –19 C h: Planks Constant= 6.63 x 10 -34 J·s eV: electron volts, 1eV= 1.60 x10 –19 J n=1,2, 3, … Principal quantum number n=3 n=2 Definite Energy Levels (2) n=1 ev h n me E n 2 2 2 4 2 6 . 13 2 = = -1.5eV n= n=4 n=3 .. .. .. Discrete energy levels Chapter 2 ME 201: Materials Science, Z. Hao 8 n=3 n=2 n=1 -13.6eV -3.4eV n=2 Transitions (1) Emit Absorb ± The process: an electron moves from one energy level to another ± Energy involved ¾ Energy is absorbed to move to a higher energy level.
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Chapter_2 - The structure of atoms Chapter 2 Atomic...

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