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Bonding

Bonding. Why do elements bond?. Bonding results in greater stability Through sharing electrons- covalent Through transfer of electrons- ionic Compounds have different properties than elements Sodium Chloride vs. Sodium and Chlorine. Bonding & Stability.

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Bonding

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  1. Bonding

  2. Why do elements bond? • Bonding results in greater stability • Through sharing electrons- covalent • Through transfer of electrons- ionic • Compounds have different properties than elements • Sodium Chloride vs. Sodium and Chlorine

  3. Bonding & Stability • Octet Rule- elements will bond to reach a stable number of valence electrons- 8 • Exceptions: • H, He, Li, Be, B stable with 2 • S and P often have more than 8 • Period 3 and beyond sometimes have more than 8 • Noble gases don’t form compounds because they have 8 valence electrons already • They are stable alone

  4. Covalent Bonds • Covalent Bonds- sharing of electrons to become stable • Results in a molecule- 2 or more atoms covalently bonded • Occurs between 2 nonmetals • Have relatively low melting points so often liquid or gas at room temperature • No ions, so do not conduct if dissolved in water • Single Covalent bond- sharing of 2 electrons • Longest and weakest of the 3 covalent bonds • Double Covalent bond- sharing of 4 electrons • Triple Covalent bond- sharing of 6 electrons • Shortest and strongest

  5. Covalent Bonds

  6. Covalent Bonds

  7. Covalent Bonds

  8. Covalent Bonds • http://www.visionlearning.com/library/module_viewer.php?mid=55

  9. Covalent Bonds- Polarity • Atoms may share electrons equally- nonpolar covalent • Atoms have no partial charges • Molecules that are nonpolar have weak attractions for each other (called London Dispersion Forces) • Electronegativity difference of 0.4 or less • Atoms may share electrons unequally- polar covalent • Atoms have partial charges • Molecules that are polar have a stronger attraction for each other (called Dipole-Dipole forces) • Electronegativity difference of over 0.4 within a covalent bond

  10. Polar vs. Nonpolar • http://www.school-for-champions.com/chemistry/polar_molecules.htm

  11. Chemical Formulas • Chemical formula- used to tell us how many of each element are in a compound • Consists of element symbols and subscripts • Water has 2 hydrogen atoms and 1 oxygen atom

  12. Chemical Formulas • SiO2 • silicon- 1 Oxygen-2 • C12H22O11 • Carbon- 12 Hydrogen-22 Oxygen-11 • N2O • Nitrogen- 2 Oxygen-1

  13. Writing Lewis Dot Structures for covalent compounds • Count up total number of valence electrons • Determine the central atom • C is often the central atom • For now, the single atom will be the central atom • Bond atoms to satisfy the octet rule first • Fill in valence electrons • If all atoms are not stable, you’ll need to try double or triple bonds • If you have extra electrons, put them on the central atom • For more detailed rules: http://antoine.frostburg.edu/chem/senese/101/bonds/faq/simple-lewis-structures.shtml

  14. STOP HERE TO PRACTICE

  15. Ionic Compounds • Ionic compound - composed of cations and anions • Metal (cation) & nonmetal (anion) OR metal & polyatomic ion • Polyatomic Ions- groups of atoms that are covalently bonded and collectively have a charge • Examples of polyatomic ions: SO42- PO43-

  16. Ionic Compounds • Ionic compound - composed of cations and anions • Metal (cation) & nonmetal (anion) OR metal & polyatomic ion • Neutral overall • Total positive charge = total negative charge • Solid crystals at room temperature • Melt only at very high temperatures • Ionic Bond: The electrostatic forces that hold ions together in ionic compounds

  17. 7.2 Properties of Ionic Compounds • The orderly arrangement of component ions produces the beauty of crystalline solids.

  18. Ionic Bond Formation

  19. Sodium Chlorine Sodium Chloride http://www.dac.neu.edu/physics/b.maheswaran/phy1121/data/ch09/anim/anim0904.htm CLICK FOR ANIMATION OF IONIC and COVALENT BONDING

  20. Compare and Contrast Ionic and Covalent Bonding

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