SCH4U Lee 1.4

OCV Chemistry, Grade 12 University Preparation (SCH4U) Ottawa-Carleton Virtual Secondary School 2020-2021 Mr. Daniel Cho-En Lee ( daniel.cho-en.lee@ocdsb.ca ) Previously we examined bond hybridization of sp 3 , which involves a total of four [bonding atoms + lone pairs]. Under the VSEPR theory, the sp 3 hybridization always produces the tetrahedral shape when counting all lone pairs. sp 2 hybridization BH 3 Boron has three valence electrons. Each bonds with a hydrogen. Together they form three sp 2 hybrid orbitals. The resulting shape is trigonal planar with a bond angle of 120º. A very common sp 2 hybrid orbital is found on double-bonded carbon, such as C 2 H 4 (ethene). Each C in C 2 H 4 has three bonded atoms (C-C, C-H, C-H), which repel each other and spread out with a bond angle of 120º on a flat plane. All atoms of C 2 H 4 are on the same plane - making C 2 H 4 a flat molecule. The sp 2 flatness gives rise to critically important functions, such as the ladder-like nitrogenase base pairing of DNA (unit 2). sp 2 bond hybridization always produces the trigonal planar shape (including possible lone pairs). 1

OCV Chemistry, Grade 12 University Preparation (SCH4U) Ottawa-Carleton Virtual Secondary School 2020-2021 Mr. Daniel Cho-En Lee ( daniel.cho-en.lee@ocdsb.ca ) What about the leftover single electron in the not hybridized 2p orbital? If this electron remains unpaired, the C would be very unstable, just like F. Fortunately, there is another unpaired 2p electron on the second carbon. The two unpaired 2p electrons, one from each carbon, will pair up to form a second covalent bond. You may call that the 2p subshell contains 2p x , 2p y , and 2p z orbitals. The coplanar atoms of C 2 H 4 already occupy two axes (a 2-D plane occupies two axes), leaving a third axis empty. Therefore, the C 2p - C 2p paired orbital occupies this empty axis, which extends up and down in our drawings. The C 2p - C 2p paired orbital forms a π (pi) bond. This is the second bond of the C=C bond. (The first bond of C=C, the C sp 2 - C sp 2 , is still a sigma bond.) The two bonds in a double bond are not the same bonds. Clarification: Each π (pi) bond contains two electrons. The pi bond is both above and below the plane. Both electrons are both above and below the plane. 2

OCV Chemistry, Grade 12 University Preparation (SCH4U) Ottawa-Carleton Virtual Secondary School 2020-2021 Mr. Daniel Cho-En Lee ( daniel.cho-en.lee@ocdsb.ca ) Exercise 4. Draw an orbital diagram of a nitrogen molecule (N N) and then an oxygen molecule (O=O), pointing out ≡ the orbitals responsible for and π bonds, respectively. Then, draw all electron clouds of N ? 2 and O 2 , including lone pair electrons, according to the VSEPR theory (so that a lone pair e - is equivalent to a bonded atom while deciding the shape of a molecule). What is the bond hybridization of N and O? Answers (don’t peek): https://docs.google.com/presentation/d/1bWm56zyPZu05reCBTw1ws_6SDfv-Oul19r4EA7JDntQ/edit?usp=sharing Exercise 5 . Come up with an orbital diagram of carbon dioxide (CO 2 , O=C=O). What is the bond hybridization of the C? According to the VSEPR theory, what is the bond hybridization of each O? Exercise 6 . Compare (sigma) bond and π (pi) bond ? comparison criteria (sigma) bond ? π (pi) bond Must contain orbital: s or p? s p Location right in between two nuclei above and below, front and back Can it be hybridized? yes no Examples First bond of O=O Second bond of O=O Exercise 7. Compare single, double, and triple bonds comparison criteria Single bond Double bond Triple bond composition /π) (? bond ? bond + π bond ? bond + 2π bonds ? location right in between two nuclei Right in between two nuclei Above and below Right in between two nuclei Above and below Front and back examples C 2 H 6 C 2 H 4 C 2 H 2 4

OCV Chemistry, Grade 12 University Preparation (SCH4U) Ottawa-Carleton Virtual Secondary School 2020-2021 Mr. Daniel Cho-En Lee ( daniel.cho-en.lee@ocdsb.ca ) Exercise 8 . For each of the molecules below, focus on the central atom. First list the orbital hybridization, and then the orbitals involved in hybridization in each case. CO 2 SO 2 NH 3 BCl 3 sp sp 2 sp 3 sp 2 2s, 2p 3s, 3p, 3p(lone pair) 2s, 2p, 2p, 2p(lone pair) 2s, 2p, 2p Exercise 9. Compare bond hybridizations comparison criteria sp sp 2 sp 3 Number of orbitals involved 2 3 4 Shape linear trigonal planar tetrahedral Theoretical bond angle 180º 120º 109.5º Examples CO 2 BF 3 CH 4 Kahoot! End of Quiz #2 coverage Quiz #2 from previous cohort https://docs.google.com/document/d/1fOFgCXLcaoZXS_kPBFMlHySSj0DK8YE5YOEfDOT1YLc/edit?usp=sharing Extended topics Ripen fruit with plant hormone ethene (old name: ethylene) https://www.youtube.com/watch?v=WtVtikkrdeE Cut metal with an oxygen-ethyne (old name: acetylene) torch https://www.youtube.com/watch?v=7EGmrPiumEU 5

OCV Chemistry, Grade 12 University Preparation (SCH4U) Ottawa-Carleton Virtual Secondary School 2020-2021 Mr. Daniel Cho-En Lee ( daniel.cho-en.lee@ocdsb.ca ) charge of the anion. 7