Chemistry 104 Chapter Five PowerPoint Notes - 104 Chapter Five PowerPoint Notes Page1 Chemical Bonding: ... pyramidal Molecular shape MAR Structure ... Chemistry 104 Chapter Five PowerPoint Notes

  • Published on
    11-Apr-2018

  • View
    218

  • Download
    6

Embed Size (px)

Transcript

<ul><li><p>Chemistry 104 Chapter Five PowerPoint Notes</p><p>Page 1</p><p>Chemical Bonding: TheCovalent Bond Model</p><p>Chapter 5</p><p>Chemistry 104Professor Michael Russell</p><p>MAR</p><p>Covalent Bonds</p><p>A covalent bond is a bond formed by sharingelectrons between atoms.</p><p>A molecule is a group of atoms held together bycovalent bonds.</p><p>Nonmetals form covalent bonds withnonmetals. They reach the Noble Gasconfiguration by sharing an appropriatenumber of electrons.</p><p>MAR</p><p>A water molecule results when two hydrogenatoms and one oxygen atom are covalentlybonded:</p><p>MAR</p><p>Are these compounds bonded through ionic or covalentbonding?PCl5 covalent (all nonmetals)Na2O ionic (metallic sodium)SO3 covalent (all nonmetals)CaSO3 ionic (metallic calcium)SbAs ?!? metalloids go both ways!</p><p>Test Yourself</p><p>Nomenclature of covalent compoundsdifferent from ionic compounds; important</p><p>to know the difference</p></li><li><p>Chemistry 104 Chapter Five PowerPoint Notes</p><p>Page 2</p><p>MAR</p><p>Naming Molecular Compounds</p><p>When two or more nonmetal elements combinethey form covalent compounds.</p><p>The formulas of covalent compounds arewritten with the less electronegative (i.e.more metal-like) element first.</p><p>More electronegative element gets -ide suffixUse Greek Prefixes to indicate number of</p><p>atoms present.</p><p>MAR</p><p>Greek Prefixes</p><p>1 mono 6 hexa</p><p>2 di 7 hepta</p><p>3 tri 8 octa</p><p>4 tetra 9 nona</p><p>5 penta 10 deca</p><p>MAR</p><p>Covalent compounds and nomenclature:</p><p>boron trichloride</p><p>nitrogen dioxide</p><p>sulfur trioxide</p><p>MAR</p><p>Test Yourself - Covalent BondingGive the names for the following formulas:N2O5SO2OF2P2O3NOGive the formulas for the following names:tetraphosphorus decaoxidecarbon dioxidecarbon monoxidenitrogen dioxide</p><p>dinitrogen pentaoxidesulfur dioxideoxygen difluoridediphosphorus trioxidenitrogen monoxide</p><p>P4O10CO2CONO2</p><p>Practice, practice, practice!</p></li><li><p>Chemistry 104 Chapter Five PowerPoint Notes</p><p>Page 3</p><p>MAR</p><p>When atoms come together, electrical interactions occur.Some interactions are repulsive:</p><p>positively charged nuclei repel each othernegatively charged electrons repel each other.</p><p>Other interactions are attractive:nucleus A attracts electrons in atom B and vice-versa</p><p>If attractive forces &gt; repulsive forcescovalent bond formed</p><p>MAR</p><p>A covalent bond between two hydrogen atoms:</p><p>A covalent bond is the result of attractive andrepulsive forces between atoms.</p><p>MAR</p><p>1s orbitals on two individual H atoms bendtogether and overlap to give egg shaped regionin the hydrogen molecule - the covalent bond.</p><p>This shared pair of electrons in a covalentbond often represented as a line between atoms.</p><p>MAR</p><p>A Bond length is the optimum distancebetween nuclei in a covalent bond.If atoms too far apart:</p><p>attractive forces are smallno bond forms</p><p>If atoms are too close:repulsive forces strongpushes atoms apartno bond forms</p></li><li><p>Chemistry 104 Chapter Five PowerPoint Notes</p><p>Page 4</p><p>MAR</p><p>A graph of potential energy versusinternuclear distance for hydrogen.</p><p>MAR</p><p>When two chlorine atoms approach each other,the unpaired 3p electrons are shared by bothatoms in a covalent bond.Each chlorine atom in the Cl2 molecule has 7electrons in its own valence shell, and sharingone more gives each valence shell an octet.</p><p>MAR</p><p>In addition to H2 and Cl2, five other elementsalways exist as diatomic molecule.</p><p>MAR</p><p>HaveNoFearOfIceClearBrew</p><p>Elements that Exist asDiatomic Molecules</p></li><li><p>Chemistry 104 Chapter Five PowerPoint Notes</p><p>Page 5</p><p>MAR</p><p>Have - Hydrogen, H2No - Nitrogen, N2Fear - Fluorine, F2Of - Oxygen, O2Ice - Iodine, I2Clear - Chlorine, Cl2Brew - Bromine, Br2</p><p>Elements that Exist asDiatomic Molecules</p><p>"HONClBrIF"</p><p>MAR</p><p>Covalent Bonds and the PeriodicTable</p><p>Covalent bonds can form between unlike atoms aswell, making possible a vast number of molecularcompounds.</p><p>Water, H2O, consists of two hydrogen atoms joined bycovalent bonds to one oxygen atom.</p><p>Ammonia, NH3, consists of three hydrogen atomsjoined by covalent bonds to one nitrogen atom.</p><p>In most covalent molecules, each atom shares enoughelectrons to achieve a noble gas configuration.</p><p>MAR</p><p>Fig 5.4 For P, S, Cl, and other elements in the third period andbelow, the number of covalent bonds may vary, as indicated bythe numbers shown in parentheses.</p><p>MAR</p><p>Multiple Covalent BondsSingle bond: A bond formed by sharing two</p><p>electrons or one pair represented by asingle line between the atoms.</p><p>Double bond: A bond formed by sharing fourelectrons or two pairs represented by twolines (=) between the atoms.</p><p>Double bond</p><p>Single bond</p></li><li><p>Chemistry 104 Chapter Five PowerPoint Notes</p><p>Page 6</p><p>MAR</p><p>Triple bond: A bond formed by sharing sixelectrons or three pairs represented by threelines () between the atoms.</p><p>MAR</p><p>Coordinate Covalent BondsCoordinate Covalent Bond: The covalent bondthat forms when both electrons are donated by thesame atom.</p><p>MAR</p><p>Molecular Formulas and LewisStructures</p><p>Molecular Formula: A formula that shows thenumber and kind of atoms in a moleculeStructural formula: Molecular representationthat shows the connections among atoms byusing lines to represent covalent bonds</p><p>Example for water:H2O = molecular formulaH-O-H = structural formula</p><p>MAR</p><p>Lewis structure: Molecular representationshowing both the connections among atomsand the locations of lone pair valenceelectrons.A lone pair is a pair of electrons not used forbonding.</p><p>Lewis structure example for water:lone pair electrons</p><p>single bond (bonding electrons)</p></li><li><p>Chemistry 104 Chapter Five PowerPoint Notes</p><p>Page 7</p><p>MAR</p><p>Drawing Lewis StructureTo draw a Lewis structure, you need to knowthe connections among atoms.Knowing common bonding patterns simplifieswriting Lewis structure.</p><p>MAR</p><p>Building a Lewis Dot StructureAmmonia, NH31. Decide on central atom; never H. Central atom is atom of lowest affinity</p><p>for electrons (usually first atom listed) Therefore, N is central2. Count valence electrons H = 1 and N = 5 Total = (3 x 1) + 5 = 8 electrons or 4 pairs</p><p>Pairs can be lone or bonding</p><p>MAR</p><p>3. Form a covalent bondbetween the central atomand surrounding atoms.</p><p>4. Remaining electrons formLONE PAIRS to complete octetas needed.</p><p>Building a Lewis Dot Structure</p><p>3 BOND PAIRS and 1 LONE PAIR.Note that N has an octet (8 electrons),</p><p>while H shares only 2 electronsMAR</p><p>Lewis structure rules:1: Decide on a central atom and find the total</p><p>number of valence electrons in molecule orion</p><p>2: Draw a line between each pair of connectedatoms to represent a covalent bond</p><p>3: Add lone pairs so that each peripheral atom(except H) gets an octet</p><p>4: Place all remaining electrons on the centralatom</p><p>5: If central atom does not have an octet, takelone pair(s) from neighboring atom(s) andform multiple bond(s) to the central atom</p></li><li><p>Chemistry 104 Chapter Five PowerPoint Notes</p><p>Page 8</p><p>MAR</p><p>Carbon Dioxide, CO21. Central atom = _______2. Valence electrons = __ or __ pairs3. Form single bonds.</p><p> This leaves 6 pairs.4. Place lone pairs on outer atoms.</p><p>MAR</p><p>Carbon Dioxide, CO24. Place lone pairs on outer atoms.</p><p>5. So that C has an octet, we shall formDOUBLE BONDS between C and O.</p><p>Practice, practice, practice!</p><p>MAR</p><p>Shape of MoleculesMolecular shapes can be predicted by notinghow many bonds and electron pairs surroundindividual atoms and applying valence-shellelectron-pair repulsion (VSEPR) theory.Basic idea of VSEPR: negatively chargedelectron clouds in bonds and lone pairs repeleach other, keeping them as far apart as possible</p><p>MAR</p><p>VSEPR</p></li><li><p>Chemistry 104 Chapter Five PowerPoint Notes</p><p>Page 9</p><p>MAR</p><p>To apply VSEPR theory:1: Draw the Lewis structure of the molecule and</p><p>identify the central atom2: Count the number of electron charge clouds</p><p>(lone and bonding pairs) surrounding thecentral atom.</p><p>3: Predict molecular shape by assuming thatclouds orient so they are as far away fromone another as possible.</p><p>VSEPR Rules</p><p>MAR</p><p>VSEPR Shape Predictor Table - Table 5.1</p><p>4</p><p>4</p><p>4</p><p>3</p><p>3</p><p>2</p><p>Clouds</p><p>2</p><p>3</p><p>4</p><p>2</p><p>3</p><p>2</p><p>Bonds</p><p>2</p><p>1</p><p>0</p><p>1</p><p>0</p><p>0</p><p>LonePairs</p><p>tetrahedral</p><p>tetrahedral</p><p>tetrahedral</p><p>planartriangular</p><p>planartriangular</p><p>linear</p><p>ElectronPair Geom.</p><p>bent</p><p>pyramidal</p><p>tetrahedral</p><p>bent</p><p>planartriangular</p><p>linear</p><p>MolecularShape</p><p>109</p><p>109</p><p>109</p><p>120</p><p>120</p><p>180</p><p>Angles</p><p>always polar</p><p>always polar</p><p>always polar</p><p>Notes</p><p>tetrahedral EPG,pyramidal Molecularshape</p><p>MAR</p><p>Structure Determination byVSEPR</p><p>Ammonia, NH31. Draw Lewis electron dot structure2. Count Electron charge clouds(bonds and lone pairs) = 43. The 4 electron pairs are at thecorners of a tetrahedron.</p><p>MAR</p><p>Structure Determination byVSEPR</p><p>Ammonia, NH3There are 4 electron pairs at the corners</p><p>of a tetrahedron.</p><p>The ELECTRON PAIR GEOMETRY istetrahedral.</p></li><li><p>Chemistry 104 Chapter Five PowerPoint Notes</p><p>Page 10</p><p>MAR</p><p>Ammonia, NH3The electron pair geometry is tetrahedral.</p><p>The MOLECULAR GEOMETRY the positions ofthe atoms is PYRAMIDAL.</p><p>Structure Determination byVSEPR</p><p>MAR</p><p>Describe the Lewis structure, electron pairgeometry and molecular shape of methane, CH4.</p><p>Number of valence electrons = 4 + 1(4) = 8Number of electron pairs = 4Central atom = CLewis structure: C in the middle of four H atoms,</p><p>each connected by one lone pairThe electron pair geometry is tetrahedral.The molecular shape is also tetrahedral .</p><p>Test Yourself</p><p>MAR</p><p>Polar Covalent Bonds andElectronegativity</p><p>Electrons in a covalent bond occupy the regionbetween the bonded atoms.</p><p>If atoms in bond identical (H2, Cl2, etc.) electronsare attracted equally to both atoms and areshared equally.</p><p>If atoms in bond different (HCl, HF, etc.) electronsmay be attracted more strongly by one atomthan by the other and are shared unequally.</p><p>Such bonds are known as polar covalent bonds.</p><p>MAR</p></li><li><p>Chemistry 104 Chapter Five PowerPoint Notes</p><p>Page 11</p><p>MAR</p><p>In HCl, electrons spend more time near Cl than H.Although molecule is overall neutral, the chlorine ismore negative than the hydrogen, resulting in partialcharges on the atoms.</p><p>Partial charges represented by placing - on the morenegative atom and + on the more positive atom.</p><p>Ability of an atom to attract electrons is called theatoms electronegativity.</p><p>Fluorine, the most electronegative element, assigned avalue of 4, and less electronegative atoms assignedlower values</p><p>MAR</p><p>Electronegativities and the periodic table</p><p>MAR</p><p>Polar Molecules</p><p>Entire molecule can be polar if electrons areattracted more strongly to one part of themolecule than another.</p><p>Molecules polarity is due to the sum of allindividual bond polarities and lone-paircontributions in the molecule.</p><p>MAR</p><p>Molecular polarity is represented by an arrowpointing at the negative end and is crossed atthe positive end to resemble a positive sign.</p></li><li><p>Chemistry 104 Chapter Five PowerPoint Notes</p><p>Page 12</p><p>MAR</p><p>Molecular polarity depends on the shape of themolecule as well as the presence of polarcovalent bonds and lone-pairs</p><p>MAR</p><p>Test Yourself</p><p>nonpolar polar polar</p><p>Are BF3, Cl2CO, and NH3 polar or nonpolar?</p><p>To review and study for Chapter 5, look atthe "Concepts to Remember" at the end</p><p>of Chapter Five</p><p>End of Chapter 5</p></li></ul>