Major Concepts of Physics PHY 102 – Lecture #19: Covalent and Ionic Bonds in Physics - Pro, Study notes of Physics

Download Major Concepts of Physics PHY 102 – Lecture #19: Covalent and Ionic Bonds in Physics - Pro and more Study notes Physics in PDF only on Docsity! 1 Major Concepts of Physics PHY 102 – Lecture #19 12009Syracuse University Lecture #19 Molecules: Covalent and Ionic Bonds April 1st Spring 2009 Prof. Liviu Movileanu http://physics.syr.edu/courses/PHY102.07Spring/index.html lmovilea@physics.syr.edu Room 211, Physics Bldg., 443-8078 Major Concepts of Physics PHY102 Major Concepts of Physics PHY 102 – Lecture #19 22009Syracuse University 1. Review Conceptual example 28.1 Electron diffraction experiment 2. Covalent bond. Lewis structures of molecules 3. Ionic bonds 4. Potential-energy diagrams 5. Announcements Lecture objectives 2 Conceptual example Major Concepts of Physics PHY 102 – Lecture #19 32009Syracuse University Major Concepts of Physics PHY102 – Lecture #19 42009Syracuse University Conceptual example 5 2 Chloride atoms Outer shells only Cl Cl Major Concepts of Physics PHY102 – Lecture #19 92009Syracuse University Example: Chloride Chlorine molecule Cl2 Molecules have no overall electric charge Molecular or covalent compounds are usually gases or liquids – they have low melting points and low boiling points Forces between molecules very weak Forces (bonds) between atoms in the molecule very strong Each outer shell has 8 electrons Electrons shared Major Concepts of Physics PHY102 – Lecture #19 102009Syracuse University Example: Chloride 6 Lewis structures for covalent compounds show the shared pairs and the unshared pairs of electrons for each atom. The electrons shared in the bond are called the BONDING electron and those unshared the NON-BONDING electrons, or LONE PAIRS Cl Cl bonding electrons non-bonding electrons Major Concepts of Physics PHY102 – Lecture #19 112009Syracuse University LEWIS DIAGRAMS FOR COVALENT COMPOUNDS Nonmetallic element + nonmetallic element -> covalent compound Formation of Cl2 Cl + Cl  Cl2 --> Cl+Cl Cl Cl Lewis diagram By forming the Cl2 molecule, each Cl atom has an octet of electrons, with two electrons shared by both Cl atoms Major Concepts of Physics PHY102 – Lecture #19 122009Syracuse University 7 With the exception of Helium, for the Group IA to VIIIA the number of valence electrons in a neutral atom is equal to the element’s group number. Major Concepts of Physics PHY102 – Lecture #19 132009Syracuse University To determine the number of valence electrons and core electrons Total number of electrons = atomic number Number of Valence electrons for the A block equals the group number Core electrons = Atomic Number – # of Valence electrons For example: Cl atomic number = 17 Total number of electrons = 17 Number of valence electrons = 7 (since Cl is located in Gr VII A) Core electrons = 17- 7 = 10 Lewis diagrams involve just the valence electrons and assumes that the core electrons are not involved in bonding and reactivity. Valence and core electrons Major Concepts of Physics PHY102 – Lecture #19 142009Syracuse University 10 NNor .. N .. N OOor .. O:: .. O H - Hor H:H    Bond energy: the amount of energy required to break a bond holding two atoms together. triple bond > double bond > single bond Bond length: the distance separating the nuclei of two adjacent atoms. single bond > double bond > triple bond Major Concepts of Physics PHY102 – Lecture #19 192009Syracuse University IONIC Bonds metallic element + nonmetallic element -> ionic compound Formation of NaCl Na --> Na+ + 1e- Cl + 1e- --> Cl- Na+ + Cl- --> NaCl Atomic number of Na = 11 Number of electrons in Na = 11 Total number of electrons in Na+ is 10 The electronic configuration of Na + is the same as Ne Major Concepts of Physics PHY102 – Lecture #19 202009Syracuse University 11 Cl has seven valence electrons. If it accepts one electron from Na, then Cl- has eight electrons completing an octet (same electronic configuration as Ar) Lewis diagrams for formation of NaCl ionic bond Na --> + 1e-Na+ Cl + 1 e- --> Cl - Na --> Cl+ Na is electropositive, Cl electronegative; Na transfers an electron to Cl Cl -Na+ Major Concepts of Physics PHY102 – Lecture #19 212009Syracuse University Major Concepts of Physics PHY102 – Lecture #19 222009Syracuse University 12 Minimum energy  stable H–H bond Short-range repulsion between H nuclei Long-range attractions between e-s(-) and H nuclei (+) (no interaction) Equilibrium distance Activation energy r0 Binding energy Major Concepts of Physics PHY102 – Lecture #19 232009Syracuse University Major Concepts of Physics PHY 102 – Lecture #19 242009Syracuse University 1. Reading: This material is not covered in the textbook 2. Homework. HW#8 is pertinent to Lasers (Lecture #18) 4. Next week: We move on “Nuclear Physics” Announcements