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Chemical Bonding

CHEMISTRY - DMCU 1233. Fakulti Kejuruteraan Mekanikal, UTeM. Lecturer: IMRAN SYAKIR BIN MOHAMAD MOHD HAIZAL BIN MOHD HUSIN NONA MERRY MERPATI MITAN. Chemical Bonding. Chapter 5. THE STABILITY OF NOBLE GAS STRUCTURE. Noble gases consist of the elements helium, neon, argon, krypton,

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Chemical Bonding

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  1. CHEMISTRY - DMCU 1233 Fakulti Kejuruteraan Mekanikal, UTeM Lecturer: IMRAN SYAKIR BIN MOHAMAD MOHD HAIZAL BIN MOHD HUSIN NONA MERRY MERPATI MITAN Chemical Bonding Chapter 5

  2. THE STABILITY OF NOBLE GAS STRUCTURE Noble gases consist of the elements helium, neon, argon, krypton, xenon, and radon • Characterised by completely filled “s”and “p” sub shells. • All gases except helium (it has 1s2 configuration) have stable s2p6 electron configuration or eight electrons in their outer most shell • Noble gases have stable electron configuration, making them extremely unreactive elements

  3. THE OCTET RULE Octet rule defines that atoms tend to gain, lose or share electrons until they are surrounded by eight valence electrons • Most elements in the periodic table tend to undergo reactions to obtain eight outer-shell electrons or the stable electron configuration of the noble gases. • The atoms of these elements may gain, lose or share electrons to obtain this stable configuration

  4. Group e- configuration # of valence e- ns1 1 1A 2A ns2 2 3A ns2np1 3 4A ns2np2 4 5A ns2np3 5 6A ns2np4 6 7A ns2np5 7 Valence electrons are the outer shell electrons of an atom. The valence electrons are the electrons that participate in chemical bonding.

  5. - - - - + Li+ Li Li Li+ + e- e- + Li+ Li+ + F F F F F F The Ionic Bond (Electrovalence) An Ionic bond is the electrostatic force that holds ions together in an ionic compound Ionic compound combine a Group IA & Group IIA metal with a halogen or oxygen [He] [Ne] 1s22s1 1s22s22p5 1s2 1s22s22p6

  6. Why should two atoms share electrons? + 8e- 7e- 7e- 8e- F F F F F F F F lone pairs lone pairs single covalent bond single covalent bond lone pairs lone pairs The Covalent Bond A covalent bond is a chemical bond in which two or more electrons are shared by two atoms. (Non metal & non metal) Lewis structure of F2

  7. single covalent bonds H H H H or H H O 2e- 2e- O 8e- O C O C O O double bonds 8e- 8e- 8e- double bonds O N N triple bond N N triple bond 8e- 8e- Lewis structure of water + + Double bond – two atoms share two pairs of electrons or Triple bond – two atoms share three pairs of electrons or

  8. Lengths of Covalent Bonds Bond Lengths Triple bond < Double Bond < Single Bond

  9. Comparison of Ionic and Covalent Compounds

  10. F H F H Polar covalent bond or polar bond is a covalent bond with greater electron density around one of the two atoms electron rich region electron poor region e- poor e- rich d+ d-

  11. Electronegativityis the ability of an atom to attract toward itself the electrons in a chemical bond. Electron Affinity - measurable, Cl is highest Electronegativity - relative, F is highest Both are related but different concepts. EA refers to an isolated atom and E refers to an atom in chemical bond. Usually, EA > then E >.

  12. 0 Covalent  2 Ionic 0 < and <2 Polar Covalent Increasing difference in electronegativity Covalent Polar Covalent Ionic partial transfer of e- share e- transfer e- Classification of bonds by difference in electronegativity Difference Bond Type

  13. Classify the following bonds as ionic, polar covalent, or covalent: The bond in CsCl; the bond in H2S; and the NN bond in H2NNH2.

  14. Generally, intermolecular forces are much weaker than intramolecular forces. Intermolecular Forces Intermolecular forces are attractive forces between molecules. Intramolecular forces hold atoms together in a molecule. • Intermolecular vs Intramolecular • 41 kJ to vaporize 1 mole of water (inter) • 930 kJ to break all O-H bonds in 1 mole of water (intra) “Measure” of intermolecular force boiling point melting point DHvap

  15. Orientation of Polar Molecules in a Solid Intermolecular Forces Dipole-Dipole Forces Attractive forces between polar molecules

  16. Ion-Dipole Interaction Intermolecular Forces Ion-Dipole Forces Attractive forces between an ion and a polar molecule

  17. Intermolecular Forces Dispersion Forces (London) Attractive forces that arise as a result of temporary dipoles induced in atoms or molecules ion-induced dipole interaction dipole-induced dipole interaction

  18. Dispersion forces usually increase with molar mass. Intermolecular Forces Dispersion Forces Continued Polarizability is the ease with which the electron distribution in the atom or molecule can be distorted. • Polarizability increases with: • greater number of electrons • more diffuse electron cloud

  19. What type(s) of intermolecular forces exist between each of the following molecules? HBr CH4 SO2

  20. Intermolecular Forces Hydrogen Bond The hydrogen bond is a special dipole-dipole interaction between they hydrogen atom in a polar N-H, O-H, or F-H bond and an electronegative O, N, or F atom. A H--B or A H--A A & B are N, O, or F

  21. Decreasing molar mass Decreasing boiling point Why is the hydrogen bond considered a “special” dipole-dipole interaction?

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