Structure, Polarity & Physical Properties

Transcription

1 tructure, Polarity & Physical Properties upplemental packet handouts I. Lewis structure, stability, and bond energies A. ydrogen, oxygen, and nitrogen are present in the atmosphere as diatomic molecular gases. All are covalent. Molecules act as discrete units Diatomic Compound itrogen, 2 Oxygen, O 2 ydrogen, 2 Atmospheric Abundance Lewis tructure Bonding tability triple bond ~80% ~20% O O double bond trace single bond inert supports combustion explosive Why is there such a great difference in reactivity (stability) among these gases? The order of stability often parallels the bond order; 3, 2, 1. tability is directly related to bond energy. Bond energy is defined as the amount of energy required to break a bond holding two atom together. triple bond > double bond > single bond Bond order trength strongest weakest 1

2 II. Lewis structures and molecular geometry A. In order to predict molecular shape, we must inspect a molecule's Lewis dot structure. B. The shape of a molecule plays a large part in determining its physical properties and chemical reactivity. Molecular Compound Methane, C 4 hydrosulfuric acid, 2 Water, 2 O Lewis tructure C O geometry tetrahedral bent bent ity non intermolecular force of attraction dispersion force dipole-dipole force hydrogen nonbonding force physical 25 C gas gas liquid III. Lewis tructure and Polarity A. Bond Polarity - hared electrons in a covalent bond show: 1. equal sharing between two bonding atoms 2. unequal sharing between two bonding atoms. a. For unequal sharing, the electrons are attracted to the more electronegative atom. b. A division is created in manner that the bond behaves as a bond dipole, like a bar magnet (two "poles" or ends, one more negative and the other more positive.) c. the covalent bond division is represented by d and d- partial charges water, 2 O hydrochloric acid, Cl δ O δ Cl unequal sharing δ hydrogen gas, 2 equal but opposite bond dipole 2

3 B. Molecular Polarity - A molecule is if 1. its centers of positive and negative charge do not coincide. 2. a molecule behaves as a dipole a 3. possesses a dipole moment. Polar Molecules ammonia gas, 3 water, 2 O onpolar Molecules methane gas, C 4 boron trifluoride, BF 3 δ δ δ additive bond dipoles δ O δ C opposing bond dipoles Cl B Cl Cl O DO T have a ET DIPOLE Polar have a ET DIPOLE Balloon Bending Water Demostration 3

4 IV. Ramifications of Molecular Geometry on Physical tate A. Changes in Physical tate and the Physical Appearance of Each tate melt boil olid (s) Liquid (l) Gas (g) freeze condense at 25 C sublimes, sublimation occurs when a solid converts to gas without going throught the liquid state. liquid at 25 C gases at 25 C really sticking around solid liquid solid rigid, has a fixed has definite volume but takes has no fixed volume or shape; moderate shape and volume the shape of physical its container attractions takes weak the physical shape and attractions volume of its container strong physical attractions sticking around when tempers flare The strength of a physical attraction between will determine how tolerant a molecule is of temperature Changes in Physical tate The addition of thermal energy (when tempers flare) causes changes in physical state physical attractions change OT chemical bonds as (temperature) thermal energy is added to a substance 4

5 B. Boiling Point In a very general sense, the conversion of a liquid to a gaseous vapor at a given pressure. ormal boiling point is the conversion of a liquid to a gas at atmospheric pressure. When a liquid boils, the pressure of the gaseous vapor equals the external pressure (atmospheric). non hydrogen bonding dipole-dipole London dispersion δ O δ O δ δ non δ Cl C δ Cl C non are high boiling than non hydrogen bonding > dipole-dipole Water (l) is higher boiling than Cl(g) UBTACE on-molecular 3D array-lattices between atoms Molecular attractions between network covalent network covalent (atomic solid) X X X X X X X X X ionic (cations-anions) M X M M X M X M M X M electrostatics metallic (sea of electrons) M e M M e M e M M e M hydrogen bonding X =,O,F X POLAR X dipolediople O-POLAR dispersion CRYTALLIE OLID network covalent (atomic solid) ionic (cations-anions) metallic (sea of electrons) POLAR O-POLAR 5

6 View the physical properties powerpoint 6