Bonding Honors Chemistry Unit 6 Bond Types Ionic: transfer of electrons Covalent: sharing electron pair(s) Metallic: delocalized electrons.

BondingBondingHonors ChemistryHonors Chemistry

Unit 6Unit 6

Bond TypesBond Types

Ionic: transfer of electronsIonic: transfer of electrons

Covalent: sharing electron pair(s)Covalent: sharing electron pair(s)

Metallic: delocalized electronsMetallic: delocalized electrons

Covalent BondsCovalent Bonds CharacteristicsCharacteristics

Low melting pointsLow melting points Don’t conduct electricityDon’t conduct electricity Most are brittle if solid, but usually gas or Most are brittle if solid, but usually gas or

liquidliquid Particle of a covalent compound is called Particle of a covalent compound is called

a molecule (most are between a molecule (most are between nonmetals)nonmetals)

Covalent BondsCovalent Bonds Two types:Two types: Polar covalent – one atom attracts shared Polar covalent – one atom attracts shared

pair of electrons more strongly (most) pair of electrons more strongly (most) sides of bond appear to be partially sides of bond appear to be partially chargedcharged

Nonpolar covalent – electrons are being Nonpolar covalent – electrons are being shared equally, no charge difference (no shared equally, no charge difference (no electronegativity difference) electronegativity difference)

usually between two atoms usually between two atoms

of same elementof same element

Terms to KnowTerms to Know

Bond axis: line joining nucleiBond axis: line joining nuclei Bond angle: angle between 2 axesBond angle: angle between 2 axes Bond length: distance between nucleiBond length: distance between nuclei Bond energy: energy to break bondBond energy: energy to break bond Bonds are not fixed Bonds are not fixed

More like a stiff springMore like a stiff spring Average position is given as bond length or Average position is given as bond length or

bond anglebond angle

MoleculesMolecules

Covalently bonded compoundsCovalently bonded compounds Diatomic molecules: always as 2 atoms Diatomic molecules: always as 2 atoms

when in element form (like Owhen in element form (like O22))

7 elements, make a 7 in the periodic table 7 elements, make a 7 in the periodic table (begin with N) and most are in group 17(begin with N) and most are in group 17

Elements:Elements:

Br, I, N, Cl, H, O, FBr, I, N, Cl, H, O, F

Naming a compound with Naming a compound with two non-metalstwo non-metals

Use the prefixes: Use the prefixes: (1) mono-, (2) di-, (3) tri-, (4) tetra-, (5) penta, (6) (1) mono-, (2) di-, (3) tri-, (4) tetra-, (5) penta, (6)

hexa-, (7) hepta-, (8) octa-, (9) nona-, (10) decahexa-, (7) hepta-, (8) octa-, (9) nona-, (10) deca If the first element listed has a quantity of just one then If the first element listed has a quantity of just one then

you don’t use mono- as a prefix.you don’t use mono- as a prefix. Put the appropriate prefix in front of the name of each Put the appropriate prefix in front of the name of each

element change the ending to element change the ending to –ide.–ide.

Example:Example: NN22OO55

Dinitrogen pentaoxideDinitrogen pentaoxide

Lewis Dot StructuresLewis Dot Structures Find the total number of valence Find the total number of valence

electrons using group numbers for each electrons using group numbers for each elementelement

Arrange atoms to form skeleton structure Arrange atoms to form skeleton structure with lines connecting the atoms. If with lines connecting the atoms. If carbon is present, it is central.carbon is present, it is central.

Otherwise, the least Otherwise, the least

electronegative element is electronegative element is

central. H is NEVER central.central. H is NEVER central.

Lewis Structures Lewis Structures (continued)(continued)

Each line counts as 2 electrons. Subtract these Each line counts as 2 electrons. Subtract these from total valence electrons.from total valence electrons.

Compare the electrons left to what each needs to Compare the electrons left to what each needs to be full. If they are the same, add unshared pairs to be full. If they are the same, add unshared pairs to give each nonmetal or metalloid a full octet (except give each nonmetal or metalloid a full octet (except H). Add all electrons to see if they equal the H). Add all electrons to see if they equal the valence electrons. (Gr2 and 13 just double their valence electrons. (Gr2 and 13 just double their electrons don’t get a full octet, Gr. 2 gets 4, Gr. 13 electrons don’t get a full octet, Gr. 2 gets 4, Gr. 13 gets 6)gets 6)

If there are not enough electrons to give each its If there are not enough electrons to give each its own dots, one more line needs to be drawn for own dots, one more line needs to be drawn for each 2 electrons you are short (2 atoms share). each 2 electrons you are short (2 atoms share). Recalculate from the valence electrons and dots Recalculate from the valence electrons and dots can be given.can be given.

Example 1Example 1

HH22OO 2(1) + 6 = 8 valence electrons2(1) + 6 = 8 valence electrons Skeleton: Skeleton:

....H-O-H H-O-H

. .. .

Subtract 2 for each line 8-4 = 4 eSubtract 2 for each line 8-4 = 4 e-- left leftPut dots to complete octet for oxygenPut dots to complete octet for oxygen

Example 2Example 2 CHCH33II 4+3(1)+7 = 14 valence electrons4+3(1)+7 = 14 valence electrons Skeleton:Skeleton: H H

||

H – C – HH – C – H ||

: I :: I : . .. .

Subtract 2 for each line 14-8 = 6 Subtract 2 for each line 14-8 = 6 ee-- left left Add dots to I to complete the octet.Add dots to I to complete the octet.

Other Examples: Other Examples: NHNH33, AlI, AlI33, SeO, SeO22, CO, CO22, SO, SO33

ResonanceResonance Using more than one Lewis structure to Using more than one Lewis structure to

explain when bonds are in between drawn explain when bonds are in between drawn structures (from lab measurements)structures (from lab measurements)

Molecular ShapeMolecular Shape Based on VSEPR theory: valence-shell Based on VSEPR theory: valence-shell

electron-pair repulsion theoryelectron-pair repulsion theory Electrons want to be as far apart as possible (like Electrons want to be as far apart as possible (like

charges repel)charges repel) Pairs around central atom will give anglesPairs around central atom will give angles

2 pairs: linear 1802 pairs: linear 180oo angle angle 3 pairs: trigonal planar 1203 pairs: trigonal planar 120oo angle angle 4 pairs: tetrahedral 109.54 pairs: tetrahedral 109.5oo angle angle

Repulsion is greater for unshared pairs: they push Repulsion is greater for unshared pairs: they push harder on shared pairs, decreasing the expected bond harder on shared pairs, decreasing the expected bond angle 2 unshared>1 shared with one unshared>2 angle 2 unshared>1 shared with one unshared>2 shared (bond angle is smaller with a lone pairshared (bond angle is smaller with a lone pair

VSEPRVSEPR Oklahoma State LinkOklahoma State Link Possible Shapes: p. 186 of bookPossible Shapes: p. 186 of book

Linear: 2 bonded atoms 180Linear: 2 bonded atoms 180oo angle angle Trigonal planar: 3 bonded atoms 120Trigonal planar: 3 bonded atoms 120oo angle angle Tetrahedral: 4 bonded atoms 109.5Tetrahedral: 4 bonded atoms 109.5oo angle angle Trigonal pyramidal: 3 bonded atoms, 1 Trigonal pyramidal: 3 bonded atoms, 1

unshared (lone pair) <109.5unshared (lone pair) <109.5oo angle (107 angle (107oo angle)angle)

Bent: 2 bonded atoms, 2 unshared (lone Bent: 2 bonded atoms, 2 unshared (lone pairs) <109.5pairs) <109.5oo angle (104.5 angle (104.5oo angle) angle)

Determining ShapeDetermining Shape Draw Lewis structureDraw Lewis structure Count bonded atoms and lone pairs Count bonded atoms and lone pairs on central on central

atom (ONLY!)atom (ONLY!) to determine shape to determine shape Example: HExample: H22O O Lewis structure:Lewis structure:

....H-O-H H-O-H

. .. .

2 shared (lines), 2 unshared (dot pairs)2 shared (lines), 2 unshared (dot pairs) Shape: bent, Angles: <109.5Shape: bent, Angles: <109.5oo angle (104.5 angle (104.5oo

angle)angle) Other Examples: NHOther Examples: NH33, AlI, AlI33, CH, CH44, HF, SO, HF, SO33

HybridizationHybridization

Hybridized orbitals merge s and p orbitals Hybridized orbitals merge s and p orbitals by borrowing empty p orbitals to put one by borrowing empty p orbitals to put one electron in each. This allows them to electron in each. This allows them to share that orbital with an electron from share that orbital with an electron from another atom in a covalent bond.another atom in a covalent bond.

The new hybrids have an energy that is The new hybrids have an energy that is in between that of s and pin between that of s and p

Examples: Be, Al & B, C & Si (& others)Examples: Be, Al & B, C & Si (& others)

Hybrid OrbitalsHybrid Orbitals

Count bonds to see how manyCount bonds to see how many

orbitals are orbitals are sp hybridssp hybrids

needed. Start with s, thenneeded. Start with s, then

add p orbitals to make add p orbitals to make enough.enough.

This names the hybrids.This names the hybrids.

spsp22 hybrids hybrids

spsp3 3 hybridshybrids

Predicting BondsPredicting Bonds

Based on electronegativity differenceBased on electronegativity difference Examples of calculation: (use table on p. Examples of calculation: (use table on p.

151)151) H-F 4.0 – 2.1 = 1.9 H-F 4.0 – 2.1 = 1.9 H-Br 2.8 – 2.1 = .7H-Br 2.8 – 2.1 = .7 H-IH-I 2.5 – 2.1 = .4 2.5 – 2.1 = .4 The greater the difference, the stronger The greater the difference, the stronger

the bondthe bond

Bond CharacterBond Character

Large difference: ionic bondLarge difference: ionic bond Small difference: covalent bondSmall difference: covalent bond Dividing line is 1.7Dividing line is 1.7

> 1.7 is ionic, < 1.7 is covalent, = > 1.7 is ionic, < 1.7 is covalent, = 1.7 1.7 is 50% ionic and 50% covalentis 50% ionic and 50% covalent

Unless bonded to the same type atom, Unless bonded to the same type atom, the bond has both ionic and covalent the bond has both ionic and covalent character (use chart on back of per. character (use chart on back of per. table)table)

Find the electronegativity difference in Find the electronegativity difference in black in the chartblack in the chart

The percent ionic character is The percent ionic character is underneath in redunderneath in red

Subtract from 100 to find the covalent Subtract from 100 to find the covalent charactercharacter

Example: H-F difference was 1.9Example: H-F difference was 1.9 Ionic character is listed as 59%, so Ionic character is listed as 59%, so

covalent character is 100-59 = 41% covalent character is 100-59 = 41% covalentcovalent

H-Br, H-IH-Br, H-I

Bonding DemoBonding Demo

Record color and intensity (brightness) as each Record color and intensity (brightness) as each bond forms in your journal, then calculate the bond forms in your journal, then calculate the % character for each bond% character for each bond

S-O S-O 3.5 – 2.5 = 1.0 difference3.5 – 2.5 = 1.0 difference 22% ionic, 78% covalent22% ionic, 78% covalent Mg-OMg-O 3.5 – 1.2 = 2.3 difference3.5 – 1.2 = 2.3 difference 74% ionic,26% covalent74% ionic,26% covalent

PolarityPolarity If charge of polar bonds is distributed If charge of polar bonds is distributed

equally in all directions, the molecule is equally in all directions, the molecule is nonpolarnonpolar If charge of polar bonds is not equal in all If charge of polar bonds is not equal in all

directions, the molecule is polardirections, the molecule is polar Look for something that makes the charge Look for something that makes the charge

asymmetrical (either of these makes it polar)asymmetrical (either of these makes it polar) Bonded atoms are not all the same element attached to Bonded atoms are not all the same element attached to

the central atomthe central atom Unshared pairs of electrons on the central atomUnshared pairs of electrons on the central atom

A polar molecule is called a dipole (has + and – A polar molecule is called a dipole (has + and – poles) poles)

Polarity is measured as dipole momentPolarity is measured as dipole moment

van der Waals Forcesvan der Waals Forces Intermolecular: Weak forces between molecules Intermolecular: Weak forces between molecules

(van der Waals forces)(van der Waals forces) Intramolecular: strong forces inside a molecule Intramolecular: strong forces inside a molecule

holding atoms together (bonds)holding atoms together (bonds) Types of van der Waals forcesTypes of van der Waals forces

Dipole-dipole: between polar moleculesDipole-dipole: between polar molecules Dipole-induced dipole: between dipole and nonpolar Dipole-induced dipole: between dipole and nonpolar

(peer pressure model)(peer pressure model) London Dispersion Forces: temporary dipoles that London Dispersion Forces: temporary dipoles that

happen because of electron movementhappen because of electron movement Induced by concentrations of electrons in nonpolar moleculesInduced by concentrations of electrons in nonpolar molecules Only attractive force operating in nonpolar substancesOnly attractive force operating in nonpolar substances 85% of force in most polar molecules (exceptions: NH85% of force in most polar molecules (exceptions: NH33, H, H22O)O)

Induced DipoleInduced Dipole

Peer pressure modelPeer pressure model

Electrons of nonpolar Electrons of nonpolar molecule are disturbed molecule are disturbed by presence of by presence of charged particle (ion or charged particle (ion or dipole)dipole)

Dipole-Induced DipoleDipole-Induced Dipole

Temporary DipoleTemporary Dipole

Movement of electrons may cause Movement of electrons may cause electron distribution to become electron distribution to become asymmetrical for an instantasymmetrical for an instant

Effects of IM ForcesEffects of IM Forces Properties are affected by IM forcesProperties are affected by IM forces Boiling and melting points give an Boiling and melting points give an

indication of how strong the IM forces areindication of how strong the IM forces are Nonpolar substances have the weakest Nonpolar substances have the weakest

IM forces: gases or lowboiling liquids IM forces: gases or lowboiling liquids (lower melting and boiling points)(lower melting and boiling points)

Polar substances have dipole forces that Polar substances have dipole forces that are stronger: liquid or solid at room temp are stronger: liquid or solid at room temp (higher melting and boiling points)(higher melting and boiling points)

Soaps and DetergentsSoaps and Detergents There are polar and nonpolar There are polar and nonpolar

sides to a soap moleculesides to a soap molecule The nonpolar side embeds or The nonpolar side embeds or

dissolves in greasy dirtdissolves in greasy dirt The polar side is attracted to The polar side is attracted to

water molecules (polar)water molecules (polar) Agitation breaks globule up into Agitation breaks globule up into

small pieces which are then small pieces which are then pulled away into the water and pulled away into the water and washed away.washed away.

Detergents have an additive to Detergents have an additive to keep soap scum from forming.keep soap scum from forming.

ChromatographyChromatography

Fractionation (separation) based on Fractionation (separation) based on polaritypolarity

Two phases:Two phases: Mobile phase: mixture to be separated Mobile phase: mixture to be separated

dissolved in liquid or gasdissolved in liquid or gas Stationary phase: solid or liquid adhering to Stationary phase: solid or liquid adhering to

a solida solid

Types: column, paper, gasTypes: column, paper, gas

Column ChromatographyColumn Chromatography Stationary phase is in a column.Stationary phase is in a column. Used for delicate separations such as Used for delicate separations such as

vitamins, hormones, and proteins.vitamins, hormones, and proteins. HPLC and ion are special kinds of HPLC and ion are special kinds of

column chromatographycolumn chromatography

Paper ChromatographyPaper Chromatography

Separation on paper into spots or lines Separation on paper into spots or lines on the stripon the strip

Has limitationsHas limitations

Gas ChromatographyGas Chromatography Used to analyze volatile liquids and gas Used to analyze volatile liquids and gas

or vapor mixtures.or vapor mixtures. Mixed with inert gas (like He) in mobile Mixed with inert gas (like He) in mobile

phasephase Interpreted by computerInterpreted by computer

Gas ChromatogramGas Chromatogram

Chromatography Chromatography ApplicationsApplications

Drug testing uses column and gas Drug testing uses column and gas chromatographychromatography

Car emissions are done with gas Car emissions are done with gas chromatographychromatography