Covalent Bonds

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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

Hydrogen gas H2

• Two H atoms sharing each other’s e-

• 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)

Remember how to do this?1s2…

• Each bond represents 2 shared e-

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!!

Non Polar Molecules

• Even distribution of charge• Examples: oxygen gas O2

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!

Go to ptable.com

• http://www.ptable.com

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

diamond

graphite

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

Your Turn

• N2O5

• Carbon dioxide.. To write this formula properly, what is dropped?• Sulfur trioxide• SF6