6.04 Polarity of Molecules

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1 6.04 Polarity of Molecules Predicting Molecular Polarity Dr. Fred mega Garces Chemistry 100 Miramar College ond Polarity

2 VSEPR Table: Revisited Valence Shell Electron-Pair Repulsion Theory (VSEPR) : # e- pr AE n Electronic Geometry ond Pair [Coord #] 2 AE 2 E A E 3 AE 3 E Linear E A E Trigonal non-bond AE n m Molecular Geometry 2 0 A 2 A Linear 3 0 A A 2 E 4 0 A 4.. A Trigonal A ent 4 AE 4 A E E E E 3 1 A 3 E Tetrahedral 2 2 A 2 E 2 A.. A.. Tetrahedral Pyramidal.. A ent ond Polarity

3 Molecules and Magnets Magnetic & Molecules Molecules possess magnet-like properties. Magnets have poles (+)- end (-) end. Molecules too can behave similarity to that of magnets with poles (dipole). Magnets: Magnet behavior - polar (with poles) n magnet behavior - nonpolar (without poles) Molecules ond Polarity

Analogy: 1. one wins: nonpolar 2. ne team wins: polar 3.

4 Symmetry and Leverage: Tug of War and Polarity The Charge distribution may cancel out (nonpolar) or there may be a net distortion (polar) Analogy: 1. one wins: nonpolar 2. ne team wins: polar 3. a) no one wins: nonpolar b) one team wins: polar c) two team wins polar ond Polarity

t all Covalent bonds are based on Mutual Sharing t all covalent bonds are made by bonding electrons being mutually shared between atoms δ δ+ δ+ δ δ+ δ+ 1.

5 t all Covalent bonds are based on Mutual Sharing t all covalent bonds are made by bonding electrons being mutually shared between atoms δ δ+ δ+ δ δ+ δ+ 1. The oxygen atom is proceeding to form a bond with the ydrogen atom 2. The oxygen atom and the hydrogen atom form bonds by sharing electrons 3. ecause oxygen has more protons than hydrogen, it has a greater attraction for the bonded electron (it has a stronger electronegativity) this gives oxygen a d - charge and hydrogen a d + charge 4. This separation of partial charge results in the polar properties of water ond Polarity

6 Compounds: Electronegativity When atoms combine to form compounds, electrons can either transfer from one atom to another, partially transfer from one atom to another or the electrons can be mutually shared between atoms. Transfer, partially transferred or equally shared: The behavior of the electrons is determined by the strength by which atoms attracts the bonding electrons. Electronegativity. The degree of which an atom attracts an electron. The greediness of an atom for bonding electrons. Small atoms with the highest ionization energy have the highest Electronegativity. Most Stingy Atoms near the north east corner of the periodic table are the most electronegative. Degree of polarity is based on difference of EN, or D c ond Polarity

7 Electronegativity When there is an unequal sharing of electrons between two atoms; the more stingy atom draws electrons bonded to itself. Electronegativity - Ability of an atom to draw bonded e- on to itself. If an atom is stingy for bonded electrons, then that atom is more electronegative that the atom it is bonded to. Unequal sharing of bonding electrons lead to dipolar bonds ond Polarity

8 Determining Molecular Polarity Flowchart (Details later) ow many central atoms? ne Dc 1 only 2 or more on central atom? on any central atom? Are all central atoms n-polar Polar *This is true for everything that has up to 4 regions of electron density (i.e., what we re studying in this class). It may not be true for other structures, such as an octahedron. Polarity depends on symmetry n-polar ond Polarity

9 Dipoles and its mechanism Recall the criteria for Covalent - Polar Covalent - Ionic Compounds Dc Molecules possessing net dipole moment are polar ond Polarity

10 Polar onds and Polar Molecules Polar onds- Electron cloud distortion due to electronegative atom drawing electrons on to itself. Polar Molecules If the electron cloud is distorted over the entire molecule (i.e., winner in the tug-of-war) then molecule is polar. npolar molecule If bonds are not polar or if polar bonds cancel each other (no winner in the tug-of-war), then molecule is non-polar ond Polarity

n the other hand the F molecule orientated themselves such that the the partially negative fluoride are orientated towards the positive charge in the magnetic

11 Polar Molecules in the presence of a magnetic field Molecules will align along a magnetic field based on their polar properties. The 2 molecules shown on the left are not influenced by a magnetic field since 2 is a nonpolar chemical. n the other hand the F molecule orientated themselves such that the the partially negative fluoride are orientated towards the positive charge in the magnetic field. This also applies to molecules with more than two element. In 2, the molecule is polar and it orientates itself in the presence of a magnetic field. te however that dichloroethyne is nonpolar and is not influenced by a magnetic field ond Polarity

Water, a special polar molecule: More later Water is a special

rdinarily, light weight molecule exist as a gas at temperatures

The special properties of water is due to its polar properties and

The molecular mechanism by which water sticks to themselves is due

-bonding will be covered more later in this chapter.

a lower density in its solid state, has a low vapor pressure among

Properties: Density - low density Surface tension - bugs walking on

12 Water, a special polar molecule: More later Water is a special molecule that is unique compared to other light weight molecule. rdinarily, light weight molecule exist as a gas at temperatures above 0 C. Example are C 4, N 2, 2, S 2, N 3. The special properties of water is due to its polar properties and its ability to stick among itself. The molecular mechanism by which water sticks to themselves is due to its polar nature and something called -bonding. -bonding will be covered more later in this chapter. As a result of this mechanism, water is a liquid at room temp, has a lower density in its solid state, has a low vapor pressure among others. Properties: Density - low density Surface tension - bugs walking on water Capillary action - method of which trees drink Specific eat Viscosity - high viscosity oiling point / melting point igher than expected: eat of fusion/vaporization Vapor pressure - low vapor pressure ond Polarity

13 Determining Molecular Polarity Flowchart (Details later) ow many central atoms? ne Dc on central atom? 1 only 2 or more inary Molecules FF NaCl CuS Mg F on any central atom? FeS r Are all central atoms n-polar Polar *This is true for everything that has up to 4 regions of electron density (i.e., what we re studying in this class). It may not be true for other structures, such as an octahedron. C Polarity depends on symmetry N n-polar ond Polarity

14 Determining Molecular Polarity Flowchart (Details later) ow many central atoms? ne Dc inary Molecules FF Mg NaCl F C FeS N CuS r ond Polarity

15 Determining Molecular Polarity Flowchart ow many central atoms? ne Dc 1 only 2 or more C or 2 on central atom? on any central atom? Are all central atoms n-polar Polar C 2 F 2 C 2 3 N 3 *This is true for everything that has up to 4 regions of electron density (i.e., what we re studying in this class). It may not be true for other structures, such as an octahedron. Polarity depends on symmetry n-polar ond Polarity F 2 CC 2 NΞC-Cl 3 CC 3

16 F F F.. C.. C S Determining Molecular Polarity.. : r.. C C C S.. r.. : Si ow many central atoms? 1 only 2 or more P C N : NP C on central atom? on any central atom? C Are all central atoms 2 N N 2 n-polar Polar Polarity depends on symmetry n-polar ond Polarity

17 F F F.. C.. C S Determining Molecular Polarity.. : r.. C C C S.. r.. : Si ow many central atoms? 1 only 2 or more P C N : NP C on central atom? on any central atom? C Are all central atoms 2 N N 2 n-polar Polar Polarity depends on symmetry n-polar ond Polarity

18 Molecular Polarity: Examples Linear e 2 (electron deficient molecule) Trigonal 3 (electron deficient molecule) Tetrahedral C 4 Pyramidal N 3 ent 2 Tetra S 2 Trig 3 N 3 - CS C 3 4 C 3 Cl S 2 CCl 2 S 3 F 2 C C PF 3 CI 4 CN NF 3 Assignment on VSEPR and Polarity Determination ond Polarity

19 Summary Key to determine Polarity of molecule. Lewis Structure Atoms with different EN - Polar. VSEPR Structure Symmetry (or distortion) of e- cloud; (tug-of-war). Central atom (A) has lone pair of electrons. Polarity Net distortion of the electron Cloud ond Polarity

Lewis Theory of Shapes and Polarities of Molecules

Lewis Theory of Shapes and Polarities of Molecules Sulfanilamide Lewis Structures and the Real 3D-Shape of Molecules Molecular Shape or Geometry The way in which atoms of a molecule are arranged in space