Bonding

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reserved. reserved. 11

BondsBonds

Forces that hold groups of Forces that hold groups of atoms together and atoms together and make them function as a make them function as a unit.unit.



Bond EnergyBond Energy

It is the energy required to It is the energy required to break a bond.break a bond.

It gives us information about It gives us information about the strength of a bonding the strength of a bonding interaction.interaction.



Ionic BondsIonic Bonds Formed from electrostatic Formed from electrostatic

attractions of closely packed, attractions of closely packed, oppositely charged ions.oppositely charged ions.

Metal + nonmetalMetal + nonmetal Formed when an atom that Formed when an atom that easily easily

losesloses electronselectrons reacts with one that reacts with one that attracts electronsattracts electrons



Achieving Noble Gas Achieving Noble Gas Electron Configurations Electron Configurations

(NGEC)(NGEC) Two nonmetalsTwo nonmetals react: They react: They shareshare electrons to achieve NGEC. electrons to achieve NGEC.

A nonmetal and a representative A nonmetal and a representative group metalgroup metal react (ionic compound): react (ionic compound): The valence orbitals of the metal are The valence orbitals of the metal are emptied to achieve NGEC. The emptied to achieve NGEC. The valence electron configuration of the valence electron configuration of the nonmetal achieves NGEC.nonmetal achieves NGEC.



Isoelectronic IonsIsoelectronic Ions

Ions containing the the same number Ions containing the the same number of electronsof electrons

(O(O22, F, F, Na, Na++, Mg, Mg2+2+, Al, Al3+3+))

OO22> F> F > Na > Na++ > Mg > Mg2+2+ > Al > Al3+3+

largest smallestlargest smallest



Figure 12.8:Figure 12.8: Ions as Ions as packed spheres.packed spheres.



Figure 12.8:Figure 12.8: Positions Positions (centers) of the ions.(centers) of the ions.



Figure 12.9:Figure 12.9: Relative sizes Relative sizes of some ions of some ions

and their and their parent atoms.parent atoms.



Covalent BondsCovalent Bonds Formed when electrons are shared Formed when electrons are shared

by nucleiby nuclei Overlapping of orbitals to share Overlapping of orbitals to share

electronselectrons Only diatomics are truly covalent! Only diatomics are truly covalent!

They share the pair of electrons They share the pair of electrons equallyequally

All other covalent bonds are polar All other covalent bonds are polar covalent – not an equal sharing of covalent – not an equal sharing of pair of electronspair of electrons



PolarityPolarity

Unequal sharing of electrons:Unequal sharing of electrons: A A molecule, such as HF, that has a molecule, such as HF, that has a center of positive charge and a center of positive charge and a center of negative charge is said to center of negative charge is said to be be polarpolar, or to have a , or to have a dipole dipole momentmoment. .



Figure 12.2:Figure 12.2: Probability Probability representations of the electron representations of the electron

sharing in HF.sharing in HF.



ElectronegativityElectronegativity

The ability of an atom in a molecule The ability of an atom in a molecule to attract shared electrons to itself.to attract shared electrons to itself.

One atom pulls the electron in closer One atom pulls the electron in closer to its nucleus than the other.to its nucleus than the other.

Trend: increase across a period due Trend: increase across a period due to increased effective charge; to increased effective charge; decreases down a period due to decreases down a period due to distance from nucleusdistance from nucleus



Figure 12.3:Figure 12.3: Electronegativity values Electronegativity values for selected elements.for selected elements.



Table 12.1Table 12.1



Figure 12.4:Figure 12.4: The three The three possiblepossible

types of bonds types of bonds..



Polar bonds vs. Polar Polar bonds vs. Polar moleculesmolecules

Molecules with polar bonds can be Molecules with polar bonds can be nonpolar overall when the polarity of nonpolar overall when the polarity of the bonds cancels outthe bonds cancels out

Methane CHMethane CH44

Carbon Dioxide COCarbon Dioxide CO22



Figure 12.5:Figure 12.5: Charge Charge distribution in the water distribution in the water

molecule.molecule.



Figure 12.5:Figure 12.5: Water molecule Water molecule behaves as if it had a positive behaves as if it had a positive

and negative end.and negative end.



Figure 12.6:Figure 12.6: Polar water molecules are Polar water molecules are

strongly attracted to positive ions strongly attracted to positive ions

by their negative ends.by their negative ends.



Figure 12.6:Figure 12.6: Polar water Polar water molecules are strongly molecules are strongly

attracted to negative ions by attracted to negative ions by their positive ends. their positive ends.



Lewis StructureLewis Structure

Shows how valence electrons are Shows how valence electrons are arranged among atoms in a arranged among atoms in a molecule.molecule.

Reflects central idea that stability Reflects central idea that stability of a compound relates to noble gas of a compound relates to noble gas electron configuration.electron configuration.



Octet RuleOctet Rule

To be stable, an atom in a molecule To be stable, an atom in a molecule needs 8 total electronsneeds 8 total electrons

These electrons come in pairsThese electrons come in pairs The pairs can be shared with another The pairs can be shared with another

atom, or unsharedatom, or unshared H and He have their own rule – the H and He have their own rule – the

Duet RuleDuet Rule



Comments About the Octet Comments About the Octet RuleRule

2nd row elements C, N, O, F 2nd row elements C, N, O, F observe the observe the octet ruleoctet rule..

2nd row elements B and Be often have 2nd row elements B and Be often have fewer than 8 electrons around fewer than 8 electrons around themselves - they are very reactive.themselves - they are very reactive.

3rd row and heavier elements 3rd row and heavier elements CAN CAN exceed the octet rule using empty exceed the octet rule using empty valence valence dd orbitals. orbitals.

When writing Lewis structures, When writing Lewis structures, satisfy satisfy octetsoctets firstfirst,, then place electrons around then place electrons around elements having elements having available available dd orbitals orbitals..

Drawing Lewis StructuresDrawing Lewis Structures Count the total number of valence electrons of all Count the total number of valence electrons of all

the elements in the compound. Add electrons for the elements in the compound. Add electrons for negative ions; subtract electrons for positive ions.negative ions; subtract electrons for positive ions.

Use pairs of electrons to attach each element to Use pairs of electrons to attach each element to the central atom (usually first atom listed)the central atom (usually first atom listed)

Give the central atom unshared pairs of electrons Give the central atom unshared pairs of electrons to satisfy the octet ruleto satisfy the octet rule

Assign the rest of the electron pairs to the other Assign the rest of the electron pairs to the other atoms (divide up evenly)atoms (divide up evenly)

If there are not enough electrons, pull pairs from If there are not enough electrons, pull pairs from the central atom to create double or triple bondsthe central atom to create double or triple bonds

If there are too many electrons, place the pairs on If there are too many electrons, place the pairs on the central atomthe central atom

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Pairs of electrons…Pairs of electrons…

Shared – between atoms Shared – between atoms (bonding pairs)(bonding pairs)

Unshared – not between atoms Unshared – not between atoms (lone pairs)(lone pairs)



Multiple BondsMultiple Bonds

When you When you don’t have enough don’t have enough valencevalence electrons to give all atoms a electrons to give all atoms a NGEC, then you might need to have NGEC, then you might need to have a double or triple bond between a double or triple bond between atoms.atoms.

These atoms CANNOT double bond: These atoms CANNOT double bond: H, F, Cl, Br, I. This is due to only one H, F, Cl, Br, I. This is due to only one available space in the shared orbital.available space in the shared orbital.



ResonanceResonance

Occurs when more than one Occurs when more than one valid Lewis structure can be written valid Lewis structure can be written for a particular molecule.for a particular molecule.

These are These are resonance structuresresonance structures. . The actual structure is an average of The actual structure is an average of the resonance structures.the resonance structures.



VSEPR ModelVSEPR Model

The structure around a given The structure around a given atom is determinedatom is determined principallyprincipally by minimizing by minimizing electron pair repulsions.electron pair repulsions.



Predicting a VSEPR Predicting a VSEPR StructureStructure

1.1. Draw Lewis structure.Draw Lewis structure.

2.2. Put pairs as far apart as possible.Put pairs as far apart as possible.

3.3. Determine positions of atoms from Determine positions of atoms from the way electron pairs are shared.the way electron pairs are shared.

4.4. Determine the name of molecular Determine the name of molecular structure from positions of the structure from positions of the atoms.atoms.



Figure 12.12:Figure 12.12: Molecular Molecular structure of methane.structure of methane.



Figure Figure 12.13:12.13:

Tetrahedral Tetrahedral arrangement arrangement of electron of electron

pairs.pairs.



Figure Figure 12.13:12.13:

Hydrogen Hydrogen atoms occupy atoms occupy

only three only three corners of the corners of the tetrahedron.tetrahedron.



Figure 12.13:Figure 12.13: The NH The NH33 molecule has the trigonal molecule has the trigonal

pyramid structure.pyramid structure.



Figure 12.14:Figure 12.14: Tetrahedral Tetrahedral arrangement of four electron arrangement of four electron

pairs around oxygen.pairs around oxygen.



Figure 12.14:Figure 12.14: Two electron Two electron pairs shared between oxygen pairs shared between oxygen

and hydrogen atoms.and hydrogen atoms.



Figure 12.14:Figure 12.14: V-shaped V-shaped molecular structure of the molecular structure of the

water molecule.water molecule.



Classification of shapes:Classification of shapes:# of e- pairs # of e- pairs # of e- pairs # of e- pairs # of e- pairs # of e- pairs shape shape bond angle bond angle examples examples (total) (bonding) (nonbonding) (total) (bonding) (nonbonding)...................................................................................................................................................... 1 1 1 1 0 0 linear linear 180 180

H-ClH-Cl........................................................................................................................................................ 2 2 2 2 0 0 linear linear 180 180

COCO22

.......................................................................................................................................................... 3 3 3 3 0 0 trigonal trigonal 120 120 BFBF33

planarplanar 3 3 2 2 1 1 bent or bent or < 120 < 120

SOSO22

V-shapedV-shaped.......................................................................................................................................................... 4 4 4 4 0 0 tetrahedral tetrahedral 109.5 109.5 CHCH44

4 4 3 3 1 1 trigonal trigonal < 109.5 < 109.5 NHNH33

pyramid pyramid (107 for NH3)(107 for NH3) 4 4 2 2 2 2 bent or bent or < 120 H< 120 H22SS V-shapedV-shaped 4 4 1 1 3 3 linear linear 180 180 H-ClH-Cl



Classification of shapes:Classification of shapes:# of e- pairs # of e- pairs # of e- pairs # of e- pairs # of e- pairs # of e- pairs shape shape bond angle bond angle examples examples (total) (bonding) (nonbonding) (total) (bonding) (nonbonding)............................................................................................................................................................................................................................................................................. ...............

5 5 5 5 0 0 trigonal trigonal 90 (axial) PCl90 (axial) PCl55

bipyramid bipyramid 120 (equatorial)120 (equatorial) 5 5 4 4 1 1 seesaw or seesaw or 90 (a) 90 (a)

SFSF44

teetertotter teetertotter < 120 (eq)< 120 (eq) 5 5 3 3 2 2 T-shaped T-shaped 90 90 ClFClF33

5 5 2 2 3 3 linear linear 180 180 XeFXeF22

............................................................................. ............................................................................. 6 6 6 6 0 0 octahedral or octahedral or 90 90 SFSF66

square bipyramidsquare bipyramid 6 6 5 5 1 1 square-based square-based 90 90 BrFBrF55

pyramidpyramid 6 6 4 4 2 2 square planar square planar 90 90 XeFXeF44

?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????? ? 6 ? 6 ? 3 ? 3 ? 3 ? 3 ? T-shaped ? T-shaped 90 90 ??? ??? ? 6 ? 6 ? 2 ? 2 ? 4 ? 4 ? linear ? linear 180 180 ??? ???



Shapes of Molecule PracticeShapes of Molecule Practice

Find this site (link on e-chalk)Find this site (link on e-chalk)

– http://employees.oneonta.edu/viningwj/sims/

– Go through all simulations on Chapter 9Go through all simulations on Chapter 9

Bonding

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