Slide 1

Honors Chemistry Slide 2 Ionic Bond Slide 3 Ionic Bonds Bond energy energy required to break a bond Atoms bond to achieve the lowest possible energy Very strong mutual attraction Ionic bonding Occurs between a metal + nonmetal Metals give up electrons and nonmetals gain them Slide 4 Binary Ionic Compounds Solid crystals Ions align themselves: To maximize attractions between opposite charges To minimize repulsion between like ions. React to achieve noble gas configuration Slide 5 Partial Ionic Character There are probably no totally ionic bonds between individual atoms More than 50% ionic character is considered ionic Problem with substances containing polyatomic ions New definition: ionic compound is any compound that conducts an electric current when melted Slide 6 Covalent Bonds The electrons in each atom are attracted to the nucleus of the other. But the electrons repel each other, and the nuclei repel each other. To reach a distance with the lowest possible energy. The distance between is the bond length. Electrons are shared between atoms Slide 7 Differences between ionic and covalent bonds. NaCl Cl 2 Phase at room temperature Solid Gas Density 2.165 g/cm 3 0.003214 g/cm 3 Melting point 801C -100.98C Boiling point 1413C -34.6C Ability of aqueous solution to conduct electricity Conduct s Does not conduct Some Physical Properties of NaCl and Cl 2 Slide 8 Covalent Bonding Two extremes: 1. Polar covalent bond. The electrons are not shared evenly. One end is slightly positive, the other negative Difference in electronegativity is indicated Difference in electronegativity between atoms tells us how polar Slide 9 H - F + - + - + - + - + - + - + - + - Slide 10 + - + - + - + - + - + - + - + - + - Slide 11 + - + - + - + - + - + - + - + - - + Slide 12 Electronegativity difference Bond Type Zero Intermediate Large Non-polar Covalent Polar Covalent Ionic Covalent Character decreases Ionic Character increases Slide 13 Example Order the following bonds according to polarity: HH ClH SH FH HH < SH < ClH < FH 0 < 0.4 < 0.9 < 1.9 Polarity of the bond increases as the difference in electronegativity increases Slide 14 Covalent Bond Energies Single bond share one pair Double bond share two pairs Triple bond share three pairs The more pairs shared, the shorter the bond length Slide 15 Metallic Bonds The electrons from metals form a sea of electrons that flow around the metal ions Called delocalized - they are not fixed in one place The metal cations and the electrons are oppositely charged and are attracted to each other Slide 16 Types of Bonds: Metallic As result of the delocalized electrons metals are: Malleable Ductile High melting and boiling points Conduct heat and electricity Slide 17 PART 2 Slide 18 Lewis Structure Shows how the valence electrons are arranged. One dot for each valence electron. A stable compound has all its atoms with a noble gas configuration. Hydrogen follows the duet rule. The rest follow the octet rule. Slide 19 Rules For Lewis Structures 1. Sum the valence electrons. 2. Use a pair to form a bond between each pair of atoms. 3. Arrange the rest to fulfill the octet rule (except for H and the duet). A line can be used instead of a pair. Example: H2O NH3 CH4 Slide 20 Exceptions to the Octet Rule BH3 Be and B often do not achieve octet Have less than an octet, for electron deficient molecules. SF 6 Third row and larger elements can exceed the octet Use 3d orbitals Slide 21 Resonance Sometime more than one valid Lewis structure is possible for a molecule Resonance structures show an average Use double arrows to indicate it is the average of the structures Example: NO3 - Slide 22 VSEPR THEORY V VALENCE S SHELL E ELECTRON P PAIR R REPULSION Predicts the shape of molecules and ions in which valence shell electron pairs are arranged about each atom so that they are kept as far away as possible, thus minimizing electron-pair repulsion Predicts the shape of molecules and ions in which valence shell electron pairs are arranged about each atom so that they are kept as far away as possible, thus minimizing electron-pair repulsion Slide 23 HOW DO WE DETERMINE SHAPE?SHAPE Draw Lewis dot diagrams Draw Lewis dot diagrams Determine how many bonding pairs Determine how many bonding pairs Determine how many lone pairs Determine how many lone pairs Use VSEPR to arrange atoms Use VSEPR to arrange atoms Draw structure Draw structure Lone pairs take more space Multiple bonds count as one pair (double or triple bonds) Remember: the more pairs shared, the shorter the bond length Lets try CCl 4 Lets try CCl 4 Slide 24 Summary of Molecular Shapes Type of Molecule Molecular Shape Atoms Bonded to Central Atom Lone Pairs of Electrons on central atom Formula Example Linear20CO2 Bent21SnF2 Slide 25 Summary of Molecular Shapes Type of Molecule Molecular Shape Atoms Bonded to Central Atom Lone Pairs of Electrons on central atom Formula Example Trigonal Planar 30BH3 Tetrahe dral 40SiH4 Slide 26 Summary of Molecular Shapes Type of Molecule Molecular Shape Atoms Bonded to Central Atom Lone Pairs of Electrons on central atom Formula Example Trigonal Pyramidal 31PCl3 Bent22SCl2 Slide 27 Summary of Molecular Shapes Type of Molecule Molecular Shape Atoms Bonded to Central Atom Lone Pairs of Electrons on central atom Formula Example Trigonal bipyramidal 50PF5 Octahedral60SeCl6 Slide 28 VSEPR Slide 29 Bond Angles ShapeBond Angles Linear180 Trigonal Planar120 Tetrahedral109.5 Trigonal Pyramidal90 - 109.5 Bent90 - 109.5 Trigonal Bipyramidal90 & 120 Octahedral90 Slide 30 WHAT IS POLARITY? type of bondshape Polarity depends on the type of bond and shape of molecule. Any molecule that has a net separation of charge (dipole moment) Ionic bonds: Polar Covalent Bonds: Nonpolar-nonpolar Polar-depends on shape Slide 31 How Do We Determine Polarity?Polarity Determine bond type Determine Shape Draw arrows showing direction of poles NONPOLAR If arrows cancel each other out: NONPOLAR POLAR If arrows go toward one direction: POLAR Slide 32 Polarity and Geometry Three shapes will cancel them out. ***** ALL BONDS MUST BE THE SAME**** Linear Slide 33 Polarity and Geometry Three shapes will cancel them out. Planar triangles 120 Slide 34 Polarity and Geometry Three shapes will cancel them out. Tetrahedral Slide 35 Polarity and Geometry Others dont cancel Bent Slide 36 Polarity and Geometry Others dont cancel Trigonal Pyramidal Slide 37 Why Do we do this? Like dissolves like! Polar molecules will dissolve in polar molecules but not in non-polar molecules