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CHEMICAL BONDS

CHEMICAL BONDS. Department of Mechanical Engineering UTH, Volos, 2019. ΧΗΜΙΚΟΙ ΔΕΣΜΟΙ. ΧΩΡΙΣ ΣΥΜΜΕΤΟΧΗ ΗΛΕΚΤΡΟΝΙΩΝ (ΗΛΕΚΤΡΟΣΤΑΤΙΚΗΣ ΦΥΣΗΣ) 1. ΔΕΣΜΟΣ Ή ΓΕΦΥΡΑ ΥΔΡΟΓΟΝΟΥ 2. VAN DER WAALS 3. LONDON Ο ΡΟΛΟΣ ΤΗΣ ΗΛΕΚΤΡΟΑΡΝΗΤΙΚΟΤΗΤΑΣ ΣΤΗΝ ΔΕΣΜΕΥΣΗ ΤΩΝ ΣΤΟΙΧΕΙΩΝ. ΜΕ ΣΥΜΜΕΤΟΧΗ ΗΛΕΚΤΡΟΝΙΩΝ

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CHEMICAL BONDS

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  1. CHEMICAL BONDS Department of Mechanical Engineering UTH, Volos, 2019

  2. ΧΗΜΙΚΟΙ ΔΕΣΜΟΙ ΧΩΡΙΣ ΣΥΜΜΕΤΟΧΗ ΗΛΕΚΤΡΟΝΙΩΝ (ΗΛΕΚΤΡΟΣΤΑΤΙΚΗΣ ΦΥΣΗΣ) 1. ΔΕΣΜΟΣ Ή ΓΕΦΥΡΑ ΥΔΡΟΓΟΝΟΥ 2. VAN DER WAALS 3. LONDON Ο ΡΟΛΟΣ ΤΗΣ ΗΛΕΚΤΡΟΑΡΝΗΤΙΚΟΤΗΤΑΣ ΣΤΗΝ ΔΕΣΜΕΥΣΗ ΤΩΝ ΣΤΟΙΧΕΙΩΝ ΜΕ ΣΥΜΜΕΤΟΧΗ ΗΛΕΚΤΡΟΝΙΩΝ ΜΕ ΚΟΙΝΗ ΣΥΝΕΙΣΦΟΡΑ e- 1. ΟΜΟΙΟΠΟΛΙΚΟΣ NON POLAR COVALENT 2. ΕΤΕΡΟΠΟΛΙΚΟΣ POLAR COVALENT • ΗΜΙΠΟΛΙΚΟΣ SEMIPOLAR ΜΕ ΜΕΤΑΦΟΡΑ e- • ΙΟΝΤΙΚΟΣ (IONIC) HIGLY POLAR 2. ΜΕΤΑΛΛΙΚΟΣ (METALLIC)

  3. Atom – the smallest unit of matter “indivisible” Helium atom

  4. electron shells • Atomic number = number of Electrons • Electrons vary in the amount of energy they possess, and they occur at certain energy levels or electron shells. • Electron shells determine how an atom behaves when it encounters other atoms

  5. Electrons are placed in shells according to rules: • The 1st shell can hold up to 2 electrons, and each shell thereafter can hold up to 8 electrons.

  6. Octet Rule = atoms tend to gain, lose or share electrons so as to have 8 electrons Gain 4 electrons • C would like to • N would like to • O would like to Gain 3 electrons Gain 2 electrons

  7. Why are electrons important? • Elements have different electron configurations • different electron configurations mean different levels of bonding

  8. Electron Dot Structures Symbols of atoms with dots to represent the valence-shell electrons 1 2 13 14 15 16 17 18 H He:      LiBe B  C  N  O : F :Ne :            Na Mg AlSiPS:Cl  :Ar :    

  9. Chemical bonds: an attempt to fill electron shells ΧΩΡΙΣ ΣΥΜΜΕΤΟΧΗ ΗΛΕΚΤΡΟΝΙΩΝ (ΗΛΕΚΤΡΟΣΤΑΤΙΚΗΣ ΦΥΣΗΣ) 1. ΔΕΣΜΟΣ Ή ΓΕΦΥΡΑ ΥΔΡΟΓΟΝΟΥ 2. VAN DER WAALS 3. LONDON ΜΕ ΣΥΜΜΕΤΟΧΗ ΗΛΕΚΤΡΟΝΙΩΝ 1. ΟΜΟΙΟΠΟΛΙΚΟΣ NON POLAR COVALENT 2. ΕΤΕΡΟΠΟΛΙΚΟΣ POLAR COVALENT • ΗΜΙΠΟΛΙΚΟΣ ΜΕ ΜΕΤΑΦΟΡΑ ΗΛΕΚΤΡΟΝΙΩΝ • ΙΟΝΤΙΚΟΣ HIGLY POLAR 2. ΜΕΤΑΛΛΙΚΟΣ

  10. IONIC BONDSare bonds formed between two ions by the transferof electrons

  11. Formation of Ions from Metals • Ionic compounds result when metals react with nonmetals • Metals loseelectrons to match the number of valence electrons of their nearest noble gas • Positive ionsform when the number of electrons are less than the number of protons Group 1 metals ion 1+ Group 2 metals ion 2+ • Group 13 metals ion 3+

  12. Formation of Sodium Ion Sodium atom Sodium ion Na  – e Na + 2-8-1 2-8 ( = Ne) 11 p+ 11 p+ 11 e- 10 e- 01+

  13. Formation of Magnesium Ion Magnesium atom Magnesium ion  Mg  – 2e Mg2+ 2-8-2 2-8 (=Ne) 12 p+ 12 p+ 12 e- 10 e- 0 2+

  14. Some Typical Ions with Positive Charges (Cations) Group 1 Group 2 Group 3 H+ Mg2+ Al3+ Li+ Ca2+ Na+ Sr2+ K+ Ba2+

  15. Fluoride Ion unpaired electron octet 1 - : F  + e: F :  2-7 2-8 (= Ne) 9 p+ 9 p+ 9 e- 10 e- 0 1 - ionic charge

  16. Ionic Bond • Between atoms of metals and nonmetals with very different electronegativity • Bond formed by transfer of electrons • Produce charged ions all states. • Conductors and have high melting point. • Examples; NaCl, CaCl2, K2O

  17. 1). Ionic bond – electron from Na is transferred to Cl, this causes a charge imbalance in each atom. The Na becomes (Na+) and the Cl becomes (Cl-), charged particles or ions.

  18. COVALENT BONDΟΜΟΙΟΠΟΛΙΚΟΣΕΤΕΡΟΠΟΛΙΚΟΣΗΜΙΠΟΛΙΚΟΣbond formed by the sharing of electrons

  19. -water is a polarmolecule because oxygen is more electronegative than hydrogen, and therefore electrons are pulled closer to oxygen.

  20. Bond Polarity and Electronegativity Electronegativity • Electronegativity: The ability of one atoms in a molecule to attract electrons to itself. • Pauling set electronegativities on a scale from 0.7 (Cs) to 4.0 (F). • Electronegativity increases • across a period and • down a group.

  21. Covalent Bond • Between nonmetallic elements of similar electronegativity. • Formed by sharing electron pairs • Stable non-ionizing particles, they are not conductors at any state • Examples; O2, CO2, C2H6, H2O, SiC

  22. Covalent Bonds

  23. Covalent Bonds Two nonmetal atoms form a covalent bond because they have less energy after they bonded H+H H : H = HH = H2 hydrogen molecule

  24. Double Covalent Bond 2 pairs of electrons are shared between 2 atoms Example O2       O  + O  O::O      double bond

  25. Triple Covalent Bond 3 pairs of electrons are shared between 2 atoms Example N2       N  + N  N:::N  triple bond

  26. Bonds in all the polyatomic ions and diatomics are all covalent bonds

  27. NONPOLAR COVALENT BONDS when electrons are equally shared H2 or Cl2

  28. Covalent bonds- Two atoms share one or more pairs of outer-shell electrons. Oxygen Atom Oxygen Atom Oxygen Molecule (O2)

  29. POLAR COVALENT BONDS when electrons are shared but sharedunequally H2O

  30. - water is a polarmolecule because oxygen is more electronegative than hydrogen, and therefore electrons are pulled closer to oxygen.

  31. METALLIC BONDbond found in metals; holds metal atoms together very strongly

  32. AND Bonds WITHOUT THE PARTICIPATION OF ELECTRONS

  33. Electronegativities of Elements Electronegativity

  34. Using the EN trends to predict bond type Increasing EN Increasing EN 105 Db 107 Bh NO RbF FeS H2S Modified from http://www.cem.msu.edu/~djm/cem384/ptable.html

  35. Chemical Bonding: The Covalent Bond Modelcont’d Abbreviated periodic table showing Pauling electronegativity values for selected representative elements.

  36. Bond Polarity and Electronegativity Electronegativity and Bond Polarity • There is no sharp distinction between bonding types. • The positive end (or pole) in a polar bond is represented + and the negative pole -.

  37. Molecular Shape and Molecular Polarity

  38. Here is the electrostatic potential map for H2CO. Show the electron migration on this planar molecule. H C O H blue – positivered - negative How is this molecule different than BF3?

  39. Chemical Bonding: The Covalent Bond Model (a) Methane is a nonpolar tetrahedral molecule. (b) Methyl chloride is a polar tetrahedral molecule.

  40. Molecular Shape and Molecular Polarity

  41. Covalent Bonding and Orbital Overlap

  42. Comparison of Bonding Types ionic covalent ions molecules molten salts conductive non- conductive valence electrons transfer of electrons sharing of electrons high mp low mp DEN > 1.7 DEN < 1.7

  43. A B A+ B- A B Increasing DEN Increasing polarity 100% covalent 100% ionic Bonding spectrum Transfer

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