chemical reactions or “bonds away” with valence electrons

Chemical Reactions or Chemical Reactions or “Bonds Away” with Valence “Bonds Away” with Valence

ElectronsElectrons Review valence electronsReview valence electrons Principles of “Bonds Away”Principles of “Bonds Away” Ionic BondsIonic Bonds Metallic BondsMetallic Bonds Covalent BondsCovalent Bonds Intermolecular ForcesIntermolecular Forces Common Chemical ReactionsCommon Chemical Reactions

Take Home MessageTake Home Message

When atoms combine to produce molecules and When atoms combine to produce molecules and compounds, expect the chemical properties of the compounds, expect the chemical properties of the molecules/compounds to be far different than that of molecules/compounds to be far different than that of the constituent atoms (the constituent atoms (hierarchy theory)hierarchy theory)

Atoms bind together by re-arranging and sharing Atoms bind together by re-arranging and sharing electronselectrons Ionic bondsIonic bonds Metallic bondsMetallic bonds Covalent BondsCovalent Bonds Intermolecular forces (e.g., hydrogen bond)Intermolecular forces (e.g., hydrogen bond)

Chemical interactions make and break bonds Chemical interactions make and break bonds between atoms and in so doing effect a change in between atoms and in so doing effect a change in energy (potential and kinetic)energy (potential and kinetic)

Weak chemical bonds (e.g., covalent bonds) play a Weak chemical bonds (e.g., covalent bonds) play a very important role in the chemistry of lifevery important role in the chemistry of life

Chapter Deletions (No. 9)Chapter Deletions (No. 9)

Pp 184 (A Closer look)Pp 184 (A Closer look) Pp 186 (A Closer Look)Pp 186 (A Closer Look) Pp 188 (Percent Composition of Pp 188 (Percent Composition of

Compounds) – 191 (Ion Exchange Compounds) – 191 (Ion Exchange Reactions)Reactions)

Valence Electrons and Valence Electrons and Chemical BondingChemical Bonding

Review valence electronsReview valence electrons Principles of “Bonds Away”Principles of “Bonds Away” Ionic BondsIonic Bonds Metallic BondsMetallic Bonds Covalent BondsCovalent Bonds Intermolecular ForcesIntermolecular Forces Common Chemical ReactionsCommon Chemical Reactions

Atoms in Proximity: “Bonds Atoms in Proximity: “Bonds Away”Away”

Hypothesis: when two atoms are brought Hypothesis: when two atoms are brought together, electrons will tend to re-arrange together, electrons will tend to re-arrange themselves to the lowest energy state themselves to the lowest energy state where the valence electrons are most stablewhere the valence electrons are most stable

Product: electrons are re-arranged into Product: electrons are re-arranged into bondsbonds Give away electronsGive away electrons Accept electronsAccept electrons Share electronsShare electrons

Ionic BondingIonic Bonding

Atoms give away electrons whereas Atoms give away electrons whereas other atoms receive electronsother atoms receive electrons

Example of lithium (Li) chloride (Cl) Example of lithium (Li) chloride (Cl) 33

66Li + Li + 171735.535.5Cl = LiClCl = LiCl


Lithium (Li)Lithium (Li)

Li gives up 1 electron and is left with 2 electrons (-) and 3 protons Li gives up 1 electron and is left with 2 electrons (-) and 3 protons (+); net positive (+) charge(+); net positive (+) charge

Chlorine (Cl)Chlorine (Cl)

Cl has 1 unpaired electron in valence shell, so Cl tends to accept Cl has 1 unpaired electron in valence shell, so Cl tends to accept an electron and is left with 18 electrons (-) and 17 protons; net an electron and is left with 18 electrons (-) and 17 protons; net negative (-) chargenegative (-) charge


Atoms give away electrons while other atoms Atoms give away electrons while other atoms receive electronsreceive electrons

Example of lithium chlorideExample of lithium chlorideLi + Cl = LiClLi + Cl = LiCl

Bonding via Bonding via electrical attractionelectrical attraction between Li+ between Li+ and Cl-and Cl- Li+ + Cl - = LiLi+ + Cl - = Li++ClCl--

Consequence: ionic bonds are underpinned by Consequence: ionic bonds are underpinned by charged charged ionsions and tend to form crystals of very and tend to form crystals of very specific and repeating geometry (very rigid)specific and repeating geometry (very rigid)

Example: NaCl is based on ionic bonds and is saltExample: NaCl is based on ionic bonds and is salt

Ionic Bonding: SaltIonic Bonding: Salt

Metallic BondsMetallic Bonds

Elements that do not give or take electrons Elements that do not give or take electrons (ionic bonds) BUT share electrons(ionic bonds) BUT share electrons

Valence electrons tend to move freely Valence electrons tend to move freely between both atoms (contrast with ionic between both atoms (contrast with ionic bonds)bonds)

Significance of sharing electrons: Significance of sharing electrons: compounds tend to show two featurescompounds tend to show two features Malleability (easily worked or pounded)Malleability (easily worked or pounded) Conductive of electricity (good conductors)Conductive of electricity (good conductors)

ExamplesExamples Gold jewelryGold jewelry Copper wireCopper wire

Covalent BondsCovalent Bonds

Extremes of behavior in bondingExtremes of behavior in bonding Accept or give away electrons (ionic bonds)Accept or give away electrons (ionic bonds) No tendency to share (noble gases)No tendency to share (noble gases)

Intermediate between these two extremes Intermediate between these two extremes butbut Do not form ionic bondsDo not form ionic bonds Do not form metallic bondsDo not form metallic bonds Yet share 1, 2, 3 and 4 electrons in unique Yet share 1, 2, 3 and 4 electrons in unique

arrangement called arrangement called covalentcovalent bonds bonds Key: Key: orbits of valence electrons are sharedorbits of valence electrons are shared so that so that

electrons are shared (and move) between valence electrons are shared (and move) between valence shells of adjacent atomsshells of adjacent atoms

Covalent BondsCovalent Bonds

Example of hydrogen fluoride (HF)Example of hydrogen fluoride (HF) 11

11H and H and 991919FF

Note: Valence shell for both atoms Note: Valence shell for both atoms are fullare full Single bond sharedSingle bond shared Double bondDouble bond

Covalent Bonds: CarbonCovalent Bonds: Carbon

661212C is a special case (profoundly important)C is a special case (profoundly important)

Valence electrons for C are 4 (1 in each orbit) Valence electrons for C are 4 (1 in each orbit) and intermediate between giving and acceptingand intermediate between giving and accepting

C - C single covalent bond (1 orbit)C - C single covalent bond (1 orbit) CC C - C two covalent bonds involving 2 orbitsC - C two covalent bonds involving 2 orbits Unique behavior of C CUnique behavior of C C

C-C-CC-C-C (or H or N or (or H or N or __)__)

CC

Behavior of Valence Electrons: Behavior of Valence Electrons: Five OptionsFive Options

No action (e.g., inert gases)No action (e.g., inert gases) Give away one or more electrons in valence Give away one or more electrons in valence

state (positive ion leading to ionic bond)state (positive ion leading to ionic bond) Accept one or more electrons to valence Accept one or more electrons to valence

state (negative ion leading to ionic bond)state (negative ion leading to ionic bond) Share an electron with many other atoms Share an electron with many other atoms

without respect to an orbit (metallic bond)without respect to an orbit (metallic bond) Share one or more electrons plus their Share one or more electrons plus their

orbits with another atom (covalent bond)orbits with another atom (covalent bond)

This Week’s Lab: This Week’s Lab: Evaporation and Chemical Evaporation and Chemical

StructureStructure

Vaporization and chemical Vaporization and chemical properties of moleculesproperties of molecules Liquid to gas state changeLiquid to gas state change State change has energy cost: State change has energy cost:

endothermic (temperature decrease)endothermic (temperature decrease) Temperature change is a function of Temperature change is a function of

chemical structure of moleculechemical structure of molecule Bonding and polarityBonding and polarity

Evaporation and Chemical Evaporation and Chemical StructureStructure

Organic compoundsOrganic compounds Carbon based or hydrocarbons bond with other Carbon based or hydrocarbons bond with other

elements via covalent bonds)elements via covalent bonds) Alkanes: C and H onlyAlkanes: C and H only

Pentane (CPentane (C55HH1212)) Alcohols: C, H and OH (hydroxyl group)Alcohols: C, H and OH (hydroxyl group)

Ethanol (CEthanol (C22HH55OH)OH) Structural formulaStructural formula

Hydrogen bonding: H bonded to N, O or F Hydrogen bonding: H bonded to N, O or F (tight bond)(tight bond)

Process: as chemical vaporizes, Process: as chemical vaporizes, temperature change is chemical specific temperature change is chemical specific and is a “window” onto the chemical and is a “window” onto the chemical structure of molecule structure of molecule

Evaporation and Chemical Evaporation and Chemical StructureStructure

Hypothesis: temperature changes with Hypothesis: temperature changes with vaporization in a manner that is vaporization in a manner that is predictable, based on the bonding predictable, based on the bonding among atoms involving C, H and OHamong atoms involving C, H and OH

MethodMethod Measure temperature change electronicallyMeasure temperature change electronically Record for 6 hydrocarbonsRecord for 6 hydrocarbons Analyze data (graphically) based on Analyze data (graphically) based on

understanding of the bonds for each understanding of the bonds for each molecule molecule

Intermolecular Forces: Intermolecular Forces: Polarization & Hydrogen Polarization & Hydrogen

BondingBonding Example of water (HExample of water (H22O)O)

++HH H H++

OO--

When one molecule’s distribution of atoms results When one molecule’s distribution of atoms results in one side of the molecule having either a + or – in one side of the molecule having either a + or – chargecharge

Resulting distribution of charges causes adjoining Resulting distribution of charges causes adjoining HH22O molecule to align itself with + and – charges to O molecule to align itself with + and – charges to be most stablebe most stable

Called “polarity” of molecule (e.g., magnet)Called “polarity” of molecule (e.g., magnet) Relate to lab exercise: greater polarity, greater Relate to lab exercise: greater polarity, greater

bonding and less evaporation (less temperature bonding and less evaporation (less temperature change)change)

Intermolecular Forces: Van Intermolecular Forces: Van der Waal Forcesder Waal Forces

In polarity, specific and rigid + and – In polarity, specific and rigid + and – fields on each molecule that does not fields on each molecule that does not change over timechange over time

When molecules converge, inevitable that When molecules converge, inevitable that electrons shift and re-distribute (e.g., electrons shift and re-distribute (e.g., planar compound)planar compound)

In re-distribution, small net attraction In re-distribution, small net attraction between molecules arise and two between molecules arise and two molecules for weak bondmolecules for weak bond Graphite pencil leadGraphite pencil lead Stack of paperStack of paper


Review valence electronsReview valence electrons Principles of “Bonds Away”Principles of “Bonds Away” Ionic BondsIonic Bonds Metallic BondsMetallic Bonds Covalent BondsCovalent Bonds Intermolecular ForcesIntermolecular Forces Common Chemical Reactions (pH)Common Chemical Reactions (pH)

Acid – Base Reaction: Acid – Base Reaction: MeasurementMeasurement

pH scalepH scale Any increase in H+ results in more acid Any increase in H+ results in more acid

solution from 7 to 0solution from 7 to 0 Any increase in OH- results in more basic Any increase in OH- results in more basic

solution from 7 to 14solution from 7 to 14 ExamplesExamples

Rainwater of 5.6 means what?Rainwater of 5.6 means what? Cell pH value of 6-8 means what?Cell pH value of 6-8 means what? Importance to biological systems and bufferingImportance to biological systems and buffering


Review valence electronsReview valence electrons Principles of “Bonds Away”Principles of “Bonds Away” Ionic BondsIonic Bonds Metallic BondsMetallic Bonds Covalent BondsCovalent Bonds Intermolecular ForcesIntermolecular Forces Common Chemical Reactions (pH)Common Chemical Reactions (pH)

Take Home MessageTake Home Message

When atoms combine to produce molecules and When atoms combine to produce molecules and compounds, expect the chemical properties of the compounds, expect the chemical properties of the molecules/compounds to be far different than that molecules/compounds to be far different than that of the constituent atoms (hierarchy theory)of the constituent atoms (hierarchy theory)

Atoms bind together by re-arranging and sharing Atoms bind together by re-arranging and sharing their electronstheir electrons Ionic bondsIonic bonds Metallic bondsMetallic bonds Covalent BondsCovalent Bonds Intermolecular forces (e.g., hydrogen bond)Intermolecular forces (e.g., hydrogen bond)

Chemical interactions make and break bonds Chemical interactions make and break bonds between atoms and in so doing effect a change in between atoms and in so doing effect a change in energy (potential and kinetic)energy (potential and kinetic)

Weak chemical bonds (e.g., covalent bonds) play a Weak chemical bonds (e.g., covalent bonds) play a very important role in the chemistry of lifevery important role in the chemistry of life

chemical reactions or “bonds away” with valence electrons

Documents

kineticweak chemical

saltvalence electrons

break bonds

bonds awayhypothesis

chemical properties

valence shell

atoms contrast

ionic bondsdo