Chem-Chapter 9.docx

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Department
Chemistry
Course
CHEM 1320
Professor
Ganley
Semester
Fall

Description
Chapter 9: Chemical Bonding l 11/1 Valence electrons are the outer shell electrons of an atom. The  valence electrons are the electrons that participate in chemical  bonding. Group econfiguration # of valence electrons 1 1A ns 1 2A ns 2 2 2 1 3A ns 2p 2 3 4A ns np 4 5A ns np 3 5 2 4 6A ns np 6 7A ns np 5 7 2 2 6 2 2  1s 2s 2p 3s 3p has 4 valence electrons Phosphorus is 1s 2s 2p 3s 3p  and has 5 valence electrons Octet Rule: Atoms tend to gain, lose or share electrons until they are  surrounded by 8 valence electrons ­Gaining/losing electrons: ions >ionic bonds ­Sharing electrons: molecules >covalent bonds Electrostatic (Lattice) Energy: Lattice energy (E): energy needed to completely separate one mole  of a solid ionic compound into gaseous ions. E=kQ Q + ­     ­­­­­­­­­­­­­­­   r Q +is the charge on the cation Q ­s the charge on the anion r is the distance between the ions Lattice energy (E) increases as Q increases and/or as r decreases 11/4  Ca(g) X Cl (g)  ▯CaCl   ▯Ca +2 + Cl ­ 2 2 Ca 179.3kJ Ca 590kJ Ca 1145kJ Cl 222 X 2 = 244kJ EA=349 X 2 = 698kJ ­795.8=179.3 + 590 + 1145 + 244 ­ 698 – LE LE=2256kJ Covalent bond: two or more electrons are shared by two atoms. Single bond: two atoms share one pair of electrons Double bond: two atoms share two pairs of electrons Triple bond: two atoms share three pairs of electrons If you have a bigger bond, you have a smaller length Example: C­C = 154   C=C = 133    C≡C = 120 Polar covalent bond or polar bond: covalent bond with greater  electron density around one of the two atoms Electronegativity is the ability of an atom to attract toward itself  the electrons in a chemical bond Electron affinity­measureable, Cl is the highest Electronegativity­relative, F is the highest Bonds: Strict: ≥2 is ionic 0
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