Post on 17-Dec-2015
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• Octet Rule must be satisfied-reach noble gas state
• What of elements that meet and cannot completely transfer e- and satisfy octet rule for each?
• H and H atom story…one happy if e- tranfer other sad
• Both atoms get one e-• Both satisfy octet rule by SHARING• Each atom must have both e-• DIRECTIONAL bond- product of shared e-• Each H atom will have full outer energy level
• Oxygen gas shares 4 valence e- or 2 pairs valence e-• Results in a double bond
• Nitrogen gas shares 3 pairs of valence e-• Results in triple bond
• Hydrogen, fluorine, nitrogen, chlorine…• BrINClOF (Chlorine is capital C lower case l)
Nature of Covalent Bonds
• Strong electrostatic attraction between shared valence e- and + nucleus
• One end of molecule has more + than – charge
Draw Lewis dots and show how water molecule shares e-
• Covalent bond VERY STRONG• Shared e- confined so bond is DIRECTIONAL
Covalent vs. Ionic Bonds
• http://www.mhhe.com/physsci/chemistry/animations/chang_7e_esp/bom1s2_11.swf
http://www.bing.com/videos/search?q=ionic+vs+covalent+bonding&FORM=VIRE3&adlt=strict#view=detail&mid=D0981F9E5
• video
H tends to share only e- Octet rule not satisfied by giving up e-
• H and Cl… HCl• Chlorine tends to grab at e-• Doesn’t want to give it up… • Uneven distribution of e- density• ELECTRONEGATIVITY becomes important
ᵟ small delta indicates charge – or + ᵟ+ H Cl ᵟ-
Result is…
• POLARITY • A partial charge separation• Electronegativity increases e- moves towards
the area• In covalent bonds, neither atom has energy to
remove e- from other atom
Example of a polar covalent molecule
• H-O-H Water H2O• Stable octet for oxygen.. Completed with
other H atom
Notice how directional the bonds are for water- a covalent molecule
• Polarity of water makes it the universal solvent.. Able to dissolve many substances..
• Not all!!
Cov vs. Ionic Bonds Electronegativity counts
• Hydrogen Gas molecule: H2
No difference of attraction of electrons between 2 atoms so ΔEN=O (Capital Delta Δ means change)Hydrogen gas is a non polar covalent moleculeWater is polar covalent
EN and bond types
• 0 = non polar cov• < 0.3 no polar cov• 0.3- 0.4 slightly polar cov• 1.0-1.7 polar cov• More and more separation of charges• If difference > 1.7 then generally ionic!
Your Turn
• Use EN # on PT to determine difference in EN between elements of a compound and type of bond formed between them.
NaBr WaterCS2
Inter and Intra prefixes
• Forces may be intra or intermolecular in nature.
• H:H molecule of hydrogen gas• Can 3rd H come into the molecule? • No Pauli Exclusion Principle• Molecules formed with hydrogen gas.• Bond very strong .. What’s in between
molecules?
BLACK Intra Forces-within molecule-RED Inter Forces- between or among molecules as
they exist in natural state
Intermolecular forces weaker than intramolecular forcesThe unit formed is called a molecule
Properties of Covalent (diatomic) Elements and Compounds
• Dull no free e-• Soft, brittle- weak intermolecular forces• Low mp and bp- weak intermolecular forces• NO conductivity as solid or molten (no
charges)• Some soluble in water Aqueous solutions DO
NOT conduct electricity at all- no free moving charged particles
• Diamond and graphite examples of Carbon in covalent bonding
• Microstructures in diamond very different from graphite
• Both covalent, both made of carbon only• Diamond- strong interactions of directionality of
carbon atoms- lattice like STRONG BONDS• Graphite- weaker bonds due to direction and spaces
between atoms allows for breakage- leaving of powder from pencil
Molecular Compounds Nomenclature
• State how many of each element in compound• Water H-O-H• FIRST: must know prefixes:1. 1. Mono2. Di3. Tri4. Tetra5. Penta6. Hexa7. Hepta8. Octa9. Nona10. Deca
• Communicate first element• Assume same name as element’s name• 2nd element “ide” notation• ONE exception: if 1 is coefficient for 1st
element then it is dropped• WATER? Dihydrogen monoxide