2Chemical BondA bond results from the attraction of nuclei for electronsAll atoms trying to achieve a stable octetIN OTHER WORDSthe p+ in one nucleus are attracted to the e- of another atomElectronegativity
3What did the atom of fluorine say to the atom ofsodium?You complete me.
4Bond Formation exothermic process ENERGY Reactants Energy released Products
5Breaking Bonds Endothermic reaction energy must be put into the bond in order to break itENERGYProductsEnergy AbsorbedReactants
6Bond StrengthStrong, STABLE bonds require lots of energy to be formed or brokenweak bonds require little E
7Is a bond forming or breaking? Strong or weak bond? Reaction TimeEnergy(KJ)energy absorbedendothermicbond breakingweak unstable bondProductsReactants
8Is a bond forming or breaking? Strong or weak bond? Reaction TimeEnergyEnergy absorbedendothermicbond breakingstrong stable bondProductsReactants
9Is a bond forming or breaking? Strong or weak bond? Energy(KJ)Reaction TimeEnergy releasedexothermicbond formationweak unstable bondReactantsProducts
10Is a bond forming or breaking? Strong or weak bond? Energy(KJ)Reaction TimeReactantsProductsEnergy releasedexothermicbond formationstrong stable bond
11Two Major Types of Bonding Ionic Bondingforms ionic compoundstransfer of e-Covalent Bondingforms moleculessharing e-
12One minor type of bonding Metallic bondingOccurs between like atoms of a metal in the free stateValence e- are mobile (move freely among all metal atoms)Positive ions in a sea of electronsMetallic characteristicsHigh mp temps, ductile, malleable, shinyHard substancesGood conductors of heat and electricity as (s) and (l)
13It’s the mobile electrons that enable me-tals to conduct electricity!!!!!!
14IONic Bondingelectrons are transferred between valence shells of atomsionic compounds aremade of ionsNOT MOLECULESionic compounds are called Salts or Crystals
15[METALS ]+ [NON-METALS ]- IONic bondingAlways formed between metals and non-metals[METALS ]+ [NON-METALS ]-Lost e-Gained e-
16IONic Bonding Electronegativity difference > 2.0 Look up e-neg of the atoms in the bond and subtractNaClCaCl2Compounds with polyatomic ionsNaNO3
23Drawing ionic compounds using Lewis Dot Structures Symbol represents the KERNEL of the atom (nucleus and inner e-)dots represent valence e-
24[Na]+ [ Cl ]- NaCl This is the finished Lewis Dot Structure How did we get here?
25Step 1 after checking that it is IONIC Determine which atom will be the +ionDetermine which atom will be the - ionStep 2Write the symbol for the + ion first.NO DOTSDraw the e- dot diagram for the – ionCOMPLETE outer shellStep 3Enclose both in brackets and show each charge
27Drawing molecules using Lewis Dot Structures Symbol represents the KERNEL of the atom (nucleus and inner e-)dots represent valence e-
28Always remember atoms are trying to complete their outer shell! The number of electrons the atoms needs is the total number of bonds they can make.Ex. … H? O? F? N? Cl? C?one two one three one four
29Methane CH4 This is the finished Lewis dot structure How did we get here?
30Step 1count total valence e- involvedStep 2connect the central atom (usually the first in the formula) to the others with single bondsStep 3complete valence shells of outer atomsStep 4add any extra e- to central atomIF the central atom has 8 valence e- surrounding it . . YOU’RE DONE!
31Sometimes . . .You only have two atoms, so there is no central atom, but follow the same rules.Check & Share to make sure all the atoms are “happy”.Cl Br H O N HCl
32O O N N DOUBLE bond TRIPLE bond atoms that share two e- pairs (4 e-) atoms that share three e- pairs (6 e-)N N
33Draw Lewis Dot Structures You may represent valence electrons from different atoms with the following symbols x, ,CO2NH3
34Draw the Lewis Dot Diagram for polyatomic ions Count all valence e- needed for covalent bondingAdd or subtract other electrons based on the chargeREMEMBER!A positive charge means it LOST electrons!!!!!
51Trigonal pyramidBall and stick modelSpace filling model
52TetrahedralBall and stick modelSpace filling model
53Intermolecular attractions Attractions between moleculesvan der Waals forcesWeak attractive forces between non-polar moleculesHydrogen “bonding”Strong attraction between special polar molecules
54van der Waals Non-polar molecules can exist in liquid and solid phases because van der Waals forces keep the molecules attracted to each otherExist between CO2, CH4, CCl4, CF4, diatomics and monoatomics
55van der Waals periodicity increase with molecular mass.Greater van der Waals force?F2 Cl2 Br2 I2increase with closer distance between moleculesDecreases when particles are farther away
56Hydrogen “Bonding” Strong polar attraction Like magnetsOccurs ONLY between H of one molecule and N, O, F of anotherH “bond”
57H is shared between2 atoms of OXYGEN or2 atoms of NITROGEN or2 atoms of FLUORINEOf2differentmolecules
58Why does H “bonding” occur? Nitrogen, Oxygen and Fluorinesmall atoms with strong nuclear chargespowerful atomsvery high electronegativities
59Intermolecular forces dictate chemical properties Strong intermolecular forces cause high b.p., m.p. and slow evaporation (low vapor pressure) of a substance.
60Which substance has the highest boiling point? HFNH3H2OWHY?Fluorine has the highest e-neg, SOHF will experience the strongest H bonding and needs the most energy to weaken the i.m.f. and boil
61The Unusual Properties of Water Unusually high boiling pointCompared to other compounds in Group 16
63H2O(s) is less dense than H2O(l) The hydrogen bonding in water(l) molecules is random. The molecules are closely packed.The hydrogen bonding in water(s) molecules has a specific open lattice pattern. The molecules are farther apart.