Covalent Bonds

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 H 2 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 mations/chang_7e_esp/bom1s2_11.swf mations/chang_7e_esp/bom1s2_11.swf

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 H 2 O 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 O 2

Cov vs. Ionic Bonds Electronegativity counts Hydrogen Gas molecule: H 2 No difference of attraction of electrons between 2 atoms so ΔEN=O (Capital Delta Δ means change) Hydrogen gas is a non polar covalent molecule Water is polar covalent

EN and bond types 0 = non polar cov < 0.3 no polar cov slightly polar cov polar cov More and more separation of charges If difference > 1.7 then generally ionic!

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Your Turn Use EN # on PT to determine difference in EN between elements of a compound and type of bond formed between them. NaBr Water CS 2

Inter and Intra prefixes Forces may be intra or intermolecular in nature. H:H molecule of hydrogen gas Can 3 rd 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 forces The 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. Mono 2.Di 3.Tri 4.Tetra 5.Penta 6.Hexa 7.Hepta 8.Octa 9.Nona 10.Deca

Communicate first element Assume same name as element’s name 2 nd element “ide” notation ONE exception: if 1 is coefficient for 1 st element then it is dropped WATER? Dihydrogen monoxide

Your Turn N 2 O 5 Carbon dioxide.. To write this formula properly, what is dropped? Sulfur trioxide SF 6