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Covalent Bonding and Molecular Compounds

Covalent Bonding and Molecular Compounds. 6.2. Molecules. Molecules – a neutral group of atoms held together by covalent bonds Molecular compound – a cmpd whose simplest units are molecules

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Covalent Bonding and Molecular Compounds

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  1. Covalent Bonding and Molecular Compounds 6.2

  2. Molecules • Molecules – a neutral group of atoms held together by covalent bonds • Molecular compound – a cmpd whose simplest units are molecules • Chemical formula – indicates relative # of atoms of each kind in a chemical compound by using atomic symbols & subscripts

  3. Molecules • Molecular formula – shows types & # of atoms combined in a single molecule of a molecular compound • Diatomic molecule – a molecule with only 2 atoms.

  4. Energy change in covalent bond formation • Bond will form when potential energy will be at lowest. • Nature favors situations when E can be reduced

  5. Energy change in H2

  6. Formation of a bond • Bond length – the average distance b/t 2 bonded atoms at their lowest potential energy • Bond energy – the E required to break a chemical bond and form neutral isolated atoms

  7. The Octet Rule • Atoms want 8 e- in their valence shell • There are exceptions like H, He, and B

  8. Electron Dot notation • EDN – an e-config notation in which only the valence e-are shown as dots around an elements symbol • What is the dot notation for F, Na, Al, Kr

  9. Lewis Structures • L-S – atomic symbol is nuclei and inner shell e-’s and dot pairs and dashes b/t atoms represent e-pairs in covalent bonds or unshared pairs • Structural formula – indicates kind, #, & arrangement of bonds but not the unshared pairs of e-’s

  10. Rules for drawing LS for multiple ion compounds • H and halogens often bind to 1 other atom and are usually on the outside or end of a molec. • Atom with lowest e-neg is often central. They have less than 7 e- and can form more than 1 bond.

  11. Rules for drawing LS for multiple ion compounds 3.When placing valence e-, put 1 e- on each side b4 pairing e-

  12. Lewis Structures • Single Bond – covalent bond where 1 pair of e-’s are shared b/t 2 atoms • Draw the Lewis structure for … H2 HF NaCl CH4 CH3I

  13. How to draw LS for more complex molecules • Draw the LS for each element • Put least electronegative element in center • Arrange other elements around central atom to satisfy octet (H only needs 2) • Change dots to lines to show bonds b/t atoms

  14. How to draw LS for more complex molecules 5. For unpaired electrons, try to form multiple bonds. 6. If octets are still not satisfied, try to move electrons around molecule.

  15. Multiple Covalent Bonds • Double bond– 2 pairs of e-’s(4e-) • Triple Bond – 3 pairs of e-’s (6e-) • What is the Lewis structure for … O2 N2 CO2 CH2O C2HCl

  16. Resonance Structures • R.S. bonding in molecule or ions that can’t be represented by a single Lewis Structure • O3 • Delocalized – e- shared b/t more than 2 atoms

  17. Ions • Complete the Lewis Structures for the following… • NH4+ OH- • CN- NO2_

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