HYBRIDIZATION THEORY

Transcription

1 HYBRIDIZATION THEORY According to carbon's orbital diagram, it should only be able to form two bonds... 1s 2s 2p But we know carbon forms 4 bonds, not 2!!! Dec 5 8:19 PM HYBRIDIZATION THEORY Scientists propose that the outermost s and p orbitals are actually combined to create 4 "hybrid" orbitals of equal energy. Carbon 1s sp 3 hybrid orbitals This explained how carbon could form 4 bonds Hybridization Theory 1

2 HYBRIDIZATION THEORY To predict the hybridization involved in a compound, simply look at the first VSEPR numbers, this tells you how many electron domains(orbitals) need to be hybridized. For example: = 4 electron domains sp 3 Carbon requires 4 hybrid orbital so it hybridizes it's outermost "s" orbital and all three of the "p" orbitals to give 4 sp 3 hybrids. Dec 5 8:32 PM HYBRIDIZATION THEORY Example: Find the hybridization of the N atom in NH 3? VSEPR # = 4 so the hybridization is sp 3 Dec 5 8:39 PM 2

3 HYBRIDIZATION THEORY Example: What is the hybridization of C in CO 2? VSEPR # = 2 Only the s orbital and 1 p orbital are needed to be hybridized so the hydridization is sp Note: The other 2 p orbitals not involved in hybridization are used to form the double bonds (called Pi bonds) Dec 5 8:41 PM 1 Which of the following would require sp 2 hybridization? A BF 3 B H 2 O C PCl 3 D F 2 E N 2 Dec 5 8:49 PM 3

4 2 What would be the hybridization found on O in OF 2? A sp B sp 2 C sp 3 D s 2 p 3 E s 3 p 3 Dec 5 8:50 PM Polarity Return to Table of Contents Polarity 4

5 Polarity of Bonds Though atoms often form compounds by sharing electrons, the electrons are not always shared equally. In a covalent bond, one atom has a greater ability to pull the shared pair toward it. Oct 24 3:50 PM Polarity of Bonds Identical atoms will have an electronegativity difference of ZERO. As a result, the bond is NONPOLAR. Oct 24 3:50 PM 5

6 Bonds and Electronegativity Bond Type Electronegativity Difference Non Polar Covalent very small or zero Polar Covalent about 0.2 to 1.6 Ionic above 1.7 (between metal & non metal) Oct 24 6:05 PM Polarity of Bonds Therefore, the fluorine end of the molecule has more electron density than the hydrogen end. H F We use the symbol to designate a dipole (2 poles). The "+" end is on the more positive end of the molecule and the arrow points towards the more negative end. Oct 24 5:54 PM 6

7 Bond Dipoles and Electronegativity When two atoms share electrons unequally, a bond dipole results. Oct 24 4:44 PM Polarity of Bonds Bond lengths, Electronegativity, Differences and Dipole Moments of the Hydrogen Halides Compound Bond Electronegativity Dipole length (A0) Difference Moment (D) HF HCl HBr HI Oct 24 3:50 PM 7

8 Polarity of Molecules But just because a molecule possesses polar bonds does not mean the molecule as a whole will be polar. For instance, in the case of CO 2 : The polar bond is shown as a dipole, the arrow points to the more negative atom. Dipoles add as vectors. Oct 23 10:09 PM Polarity of Molecules By adding the individual bond dipoles, one can determine the overall dipole moment for the molecule. For a molecule to be polar, it must a) contain one or more dipoles AND b) have these polar bonds arranged asymmetrically In other words, if all the dipoles are symmetrical, they will cancel each other out and the molecule will be NONPOLAR. Many molecules with lone pairs of electrons will be POLAR. Oct 23 10:11 PM 8

9 Polarity of Molecules These are some examples of polar & nonpolar molecules. What are their VSEPR numbers? 110(?), polar Slide for Answer Slide 431, polar for Answer Slide 440, for nonpolar Answer Slide 330, for nonpolar Answer Slide 440, for polar Answer Oct 23 10:14 PM 3 Which of these are polar molecules? A a, b B a, b, c C a, c D a, c, d E c, e Oct 24 5:03 PM 9

10 4 Sulfur trioxide (SO 3 ) is polar. True False Dec 1 3:51 PM 5 Hydrogen sulfide gas (H 2 S) is non polar. True False Dec 1 3:52 PM 10

11 6 Which of the following contains polar bonds but is a non polar molecule? A CH 4 B CS 2 C H 2 S D CF 4 E All of these are polar Dec 1 3:53 PM Mar 25 11:07 PM 11