“A” students work (without solutions manual) ~ 10 problems/night .

“A” students work (without solutions manual) ~ 10 problems/night. Alanah Fitch Flanner Hall 402 508-3119 afitch@luc.edu Office Hours W – F 2-3 pm Module #10: Covalent Bonding

FITCH Rules G1: Suzuki is Success G2. Slow me down G3. Scientific Knowledge is Referential G4. Watch out for Red Herrings G5. Chemists are Lazy C1. It’s all about charge C2. Everybody wants to “be like Mike” (grp.18) C3. Size Matters C4. Still Waters Run Deep C5. Alpha Dogs eat first General Chemistry

Properties and Measurements Property Unit Reference State Size m size of earth Volume cm3m Weight gram mass of 1 cm3water at specified Temp (and Pressure) Temperature oC, K boiling, freezing of water (specified Pressure) 1.66053873x10-24g amu (mass of 1C-12 atom)/12 quantity mole atomic mass of an element in grams Pressure atm, mm Hg earth’s atmosphere atsea level Energy: Thermal BTU 1 lb water 1 oF calorie 1 g water 1 oC Kinetic J 2kg mass moving at 1m/s Energy, of electrons energy of electron in a vacuum Electronegativity F

Bonding = sharing –electrons between repulsive + nuclei • Lewis Dot structures help us visualize sharing of electrons • Octets • Double and triple bonds • Resonance structures and No Clean Socks • Formal Charge to help distinguish between alternatives • Violations of the Octet Rule • 2 electrons • >8 electrons • Using electrons to predict the SHAPE of the molecules • VESPR • Effect of unpaired electrons on the central atom on molecular shape • Effect of Multiple bonds • How to deal with “no central atom” • Bond polarity • Effect of electronegativity difference between atoms in bond • Effect of molecular shape • How to symbolize bond polarity • Discrepancies between Electron Orbital Diagrams and VESPR • Introducing orbital hybridization, s, sp, sp2, sp3 • Using orbital hybridization to visualize resonance or smearing out • of electron density in the molecule.

Covalent bonding Patterns in abundance suggest a. periodicity b. preferred electronic configuration of elements Leading to the Rule: “Everybody wants to be “Like Mike” a. Ions: Groups 16 and 17 gain electrons; Groups 1 and 2 lose b. Other atoms share electrons to have eight electrons = COVALENT BONDING

Covalent Bonding – getting to a noble gas electron configuration by sharing electrons • Bring two elements close together • When very close the positive nuclei repel each other Repulsion of two hydrogen atoms with their Proton core + +

Repulsion of two hydrogen atoms with their proton core + e + e e e + + e + + e Repulsion is high close where Protons see each other Atoms which are far apart Do not even see each other There is no energy, repulsive Or attractive between the two Repulsion is low where Electrons shield nucleus, and where Electrons can be stabilized by both Positive charges Repulsive energy Electrons are the jelly and peanut butter between the slices of bread (protons) Attractive energy

“A” students work (without solutions manual) ~ 10 problems/night. Alanah Fitch Flanner Hall 402 508-3119 afitch@luc.edu Office Hours W – F 2-3 pm

Lewis dot structure (electron dot Structure or diagram) are diagrams that Show the bonding between atoms of A molecule based on shared “valence” shell (outer shell) electrons and shows the Presence of any “lone pair” of electrons That may exist in the covalently bonded Molecule. Gilbert Newton Lewis 1875-1946; Caltech Physical Chemist Covalent Valence = outermost shell electrons of an atom shared Latin: valere – to be strong

When the two hydrogen atoms are together, the electron configuration Looks like? He When a hydrogen atom and a fluorine atom share electrons, the Electron configuration on fluorine looks like? The “inner” shell electrons do not Show in this diagram

When the two hydrogen atoms are together, the electron configuration Looks like? He When a hydrogen atom and a fluorine atom share electrons, the Electron configuration on fluorine looks like? Only the “outer-most” or valence shell electrons Show in this Lewis Dot Structure How many valence electrons?: = last number in group

When the two hydrogen atoms are together, the electron configuration Looks like? He When a hydrogen atom and a fluorine atom share electrons, the Electron configuration on fluorine looks like? The shared pair of Electrons = covalent bond The unshared pairs of electrons are “regions of high Charge density”

When a hydrogen atom and an oxygen atom share valence electrons plus an Extra electron, the electron configuration on hydrogen and oxygen look like? Valence electrons on oxygen? Valence electrons on hydrogen? Invoking Rule: Chemists are Lazy the diagram above is too tedious to write out all the time make shared electrons (bond) a line Lewis dot structure for hydroxide The single electron pair shaired between the two bonded atoms Is called a single bond It is drawn as a line.

When two hydrogen atoms and an oxygen atom share valence electrons, the electron configuration on hydrogen and oxygen look like? Two shared electron pairs Two shared electron pairs = Two single bonds

When two hydrogen atoms and an oxygen atom share valence electrons, the electron configuration on hydrogen and oxygen look like? When three hydrogen atoms and a nitrogen atom share valence electrons, the electron configuration on hydrogen and nitrogen look like?

When two hydrogen atoms and an oxygen atom share valence electrons, the electron configuration on hydrogen and oxygen look like? When three hydrogen atoms and a nitrogen atom share valence electrons, the electron configuration on hydrogen and nitrogen look like? Valence shell of nitrogen? Three pairs of shared electrons = three single bonds

When four hydrogen atoms and two carbon atoms share valence electrons, the electron configuration on hydrogen and carbon look like? Valence shell of carbon? Two electron pairs shared is a Double bond

When two hydrogen atoms and two carbon atoms share valence electrons, the electron configuration on hydrogen and carbon look like? Three electron pairs shared is a Triple bond

Rules for Writing Lewis Dot Structures • Count the number of valence electrons (last number of group) of all atoms • a. For an anion add the appropriate extra number of electrons • b. For a cation subtract the appropriate extra number of electrons • Draw a molecular skeleton, joining by single bonds to the central atom. • a. The central is usually the atom written first in the formula (N in NH4+, S in SO2, and C in CCl4). • b. The terminal atoms are usually H, O. • c. Halogens are always terminal atoms. • Determine the number of valence electrons still available for distribution after subtracting two electrons for each single bond. • Determine the number of electrons required to complete the octet • a. H gets only two electrons • b. Other exceptions to be noted below • 5. Fill in the region required for the octet. • Make up deficit of electrons by creating double bonds • a. C, N, O, S H can only have one bond because it can share only one Electron. Poor H. Halogens have lots of electrons but really do not like to share. Greedy halogens All they want is one more to make up the Mike configuration

Draw Lewis structures of • Hypochlorite ion • Methyl alcohol • N2 • SO2 Valence shell electrons? O 6 +Cl 7 +Negative charge 1 Total electrons 14 -1Single bond -2 12 -2(6 electrons for O,Cl) 12 remaining 0 Hypochlorite? Hypo – smallest number of oxygens OCl- Skeleton

Draw Lewis structures of • Hypochlorite ion • Methyl alcohol, CH3OH • N2 • SO2 Skeleton Carbon is first in formula Hydrogen is always terminal Valence shell electrons? O 6 +C 4 +4(H) 4 Negative charge 0 Total electrons 14 -5single bonds -10 remaining 4 -octet for oxygen -4 remaining 0 Octets Carbon has its octet Hydrogen has its duet Oxygen requires 4 more electrons

Draw Lewis structures of • Hypochlorite ion • Methyl alcohol, CH3OH • N2 • SO2 Skeleton Octets Each nitrogen requires 6 more Valence shell electrons? 2N 10 Negative charge 0 Total electrons 10 -1single bond -2 Remaining 8 Octet completion -12 Difference -4 2N 10 Negative charge 0 Total electrons 10 -3 single bonds -6 Remaining 4 We are short 4 electrons for the octet, The only way to get extra ones is to Share four more electrons = triple Bond. Place the remaining 4 electrons equally On the two equal nitrogens

Skeleton, First atom in formula is central • Draw Lewis structures of • Hypochlorite ion • Methyl alcohol, CH3OH • N2 • SO2 Octets We are short 2 electrons for the octet, The only way to get extra ones is to Share two more electrons = double bond. Valence shell electrons? 2O 12 +1S 6 Negative charge 0 Total electrons 18 -2(single bonds) -4 Remaining electrons 14 Octet for S -4 2(Octet for each O) -12 Deficit? -2 2O 12 +1S 6 Negative charge 0 Total electrons 18 -3(single bonds) -6 12 Place the remaining 12 electrons to fill octets

We got this Lewis dot structure No reason not to write instead Which would lead to Is there any reason for us to Presume one of these is correct And not the other? No Grammar: double-headed arrow is used to separate resonance structures

Remember our Low Charge Density; Spectator Polyatomic Anions? No Clean Socks NO3- • N 5 • 3(O) 18 • Charge 1 • Total 24 • -single bonds -6 • Remaining 18 • Octets (6x3 O +2 for N) -20 • Deficit of 1 electron pair -2 • N 5 • 3(O) 18 • Charge 1 • Total 24 • Bonds -8 • 16 Charge is distributed over All three of the resonance Forms = one big fat marshmallow

Resonance • The “real” molecule is none of the three nitrates we drew but something intermediate to the three. • Resonance can be “assumed” or “predicted” when there are equally plausible Lewis dot structures. • Resonance forms differ only in the distribution of electrons and not in the arrangement of atoms.

Write three resonance forms for SO3 Valence electrons 4(6) 24 Sulfur central atom Three single bonds to the sulfur -3(2) -6 Remaining electrons 18 2 electrons to complete S octet -2 3(6) electrons to complete O octets = 18 -18 Deficit of two electrons = double bond -2 Valence electrons 4(6) 24 Sulfur central atom Four single bonds to the sulfur -3(2) -8 Remaining electrons 16

Formal Charge helps determine the correct Lewis Dot Structure X=number of valence e- in the free atom (last number of group) Y = number of unshared e- owned by the atom in the Lewis structure Z = number of bonding e- shared by the atom in the Lewis structure • The correct Lewis dot structure is generally the one in which • The formal charges are as close to zero as possible • Negative charge is located on the more electronegative atom

X=number of valence e- in the free atom (last number of group) Y = number of unshared e- owned by the atom in the Lewis structure Z = number of bonding e- shared by the atom in the Lewis structure Which is correct?

The Octet Rule is a form of Rule #C2- Everybody wants to be like a Noble gas In same fashion: not everybody can share enough Electrons to make up a perfect octet These guys will have 1, 2, and 3 bonds only

The Octet Rule is a form of Rule #C2- Everybody wants to be like a Noble gas In same fashion: not everybody can share enough Electrons to make up a perfect octet This guy may end up “holding the bag” Having an unpaired electron Because he is Not really Strong enough To always Get the lion’s Share of the Electrons in A covalent bond, Particularly With oxygen The unpaired electron means The compound is paramagnetic The presence of these unpaired electrons on these gases Gives rise to the many atmospheric reactions involved In ozone destruction and formation of smog. Para = paramour = love = similar orientation Dia – diatribe = against = opposite orientation

A singlet electron is also called a “free radical” Aging Hydroxy radical hydroxide Cellular membrane damage http://www.thedoctorslounge.net/oncology/articles/oxidcar/oxidcar2.htm

After hydroxyl radical cleavage and denaturing gel electrophoresis, the gel patterns differ. The unfolded RNA molecule is cleaved uniformly, giving rise to a homogeneous ladder of bands on the gel (left, bottom). The gel pattern for the folded RNA (right, bottom), in contrast, shows several region where strand cleavage is inhibited, corresponding to the sites of low solvent accessibility in the folded structure (right, top). TD Tullius, JA Greenbaum, Curr Opin Chem Biol2005, 9:127–134 (Figure 1) Commentary from grove.ufl.edu/~dmorgan/Articles/DER/Journal%20Club.ppt

The Octet Rule is a form of Rule #C2- Everybody wants to be like a Noble gas Some guys can take on more electrons because they Make use of their d orbitals these guys Have d orbitals That allow them To have more Than 8 electrons 3p 4s 3d

Draw the Lewis structure of XeF4 8+4(7) =36 electrons 4bonds = 8 electrons Remainder = 28 electrons Octets: 4(6) for F = 24 Remainder to Xe = 4

Draw the Lewis structure of XeF2 8+2(7) =22 electrons 2bonds = 4 electrons Remainder = 18 electrons Octets: 2(6) for F = 12 Remainder to Xe = 6

“A” students work (without solutions manual) ~ 10 problems/night. Alanah Fitch Flanner Hall 402 508-3119 afitch@luc.edu Office Hours W – F 2-3 pm

Can now predict SHAPE of molecule determines: how two molecules orient themselves for reaction together. Can they dock? And actually do work together in three dimensional space?

Valence Shell Electron Pair Repulsion Rule C1 = It’s all about charge Eel d Valence electron pairs surrounding an atom repel one another. Consequently, the orbitals containing those electron pairs are oriented to be as far apart as possible

Geometries of AX2-AX6 molecules X A X Repulsion of valence shell electrons in Bonds and on F push F apart to a 180o orientation

Geometries of AX2-AX6 molecules What orientation would put electrons as far apart as possible? 120o degrees apart in a “circle”

Draw Lewis structures of • CH4 Valence shell electrons? +C 4 +4(H) 4 Negative charge 0 Total electrons 8 -4single bonds -8 remaining 0 Skeleton Carbon is first in formula Hydrogen is always terminal Octets Carbon has its octet Hydrogen has its duet

How can four bonds be organized in 3-D space to be farthest apart? X X X A X

3 2 5 4 3 4 2 1 A pyramid is a space figure with a square base and 4 triangle-shaped sides. (5 “faces”) 1 A tetrahedron is a space figure and 4 triangle shaped faces. Dictionary: a four-sided solid; a Triangular pyramid

3 2 5 4 3 4 2 1 A pyramid is a space figure with a square base and 4 triangle-shaped sides. (5 “faces”) Dictionary: Square base and sloping Sides rising to an apex 1 A tetrahedron is a space figure and 4 triangle shaped faces. Dictionary: a four-sided solid; a Triangular pyramid

“A” students work (without solutions manual) ~ 10 problems/night .