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Introduction & Atomic Structure, Molecular Structure and Bonding Organic Chemistry: Introduction What Is Chemistry? Chemistry Is The Study Of Matter & The Changes It Undergoes Two Main “Branches” of Chemistry Organic Chemistry Inorganic Chemistry • Term Coined by Berzelius ~ 1807 • Matter Derived From Nonliving Things • Matter Derived From Living Things • Vast Majority of the Periodic Table • Study of Carbon Compounds (C,H,N,O) 2 Influence of Organic Chemistry Organic Chemistry Is Important to Medicine: Ancient and Modern • Plant Extracts as Medicines…Active Ingredients are Organic Compounds • Prescription Drugs….Prepared by “Synthetic Chemists” Organic Chemistry and Dyes: • 1st Solid Link of Industry and Research • $$ Derived From Research Organic Chemistry and Materials Development: • Synthetic Fibers….Nylon • Synthetic Rubber….Neoprene • Chemistry of Polymers (Plastics) 3 Organic Chemistry and You? Redox Reactions Alcohols Aldehydes Ketones Alkanes/alkenes Ethers Carboxylic acids Concentration Redox Reactions Spectrometry 4 In this unit, we will review… 1. 2. 3. 4. 5. 6. Atomic Structure Lewis Dot Structures and Formal Charge Ionic and Covalent Bonds Electronegativity and Polarity Molecular Geometry Multiple Bonds 5 1 Modern Atomic Theory Atoms have an internal structure consisting of one or more subatomic particles: proton positive charge mass = 1.673 x 10-27 kg neutron no charge mass = 1.675 x 10-27 kg electron negative charge mass = 9.109 x 10-31 kg 6 1 Most of the mass of an atom is concentrated in the nucleus, which contains one or more positively charged protons and neutrons with no electrical charge. proton neutron 7 1 One or more negatively charged electrons are in constant motion outside the nucleus. What is the overall electrical charge if the number of electrons equals the number of protons? 8 1 Valence and Core Electrons Electrons contained in the outermost shell are called ________electrons. All other electrons are called ______ electrons. e- ee- ee- How many valence electrons does this atom have? Core electrons? Which number matters more? 9 1 How many valence electrons (ve-’s) does carbon have? Calcium? What element is depicted in the image on the right? 10 2 Chemical Bonding Chemical bonds are the forces that hold atoms together in compounds. We use Lewis Dot structures to represent these atoms and compounds. C O C O 11 2 Drawing Lewis Dot Structures 1. Count total ve-’s available 2. Draw a Lewis sketch – H is never central; C is often central 3. Draw in electrons to fulfill octet and duet rules – C “likes” 8 electrons; H “likes” 2 electrons 4. Count ve-’s and compare to #2 5. If too many e-’s, make a double bond 6. Calculate formal charge (FC) to double check structure – No or low FCs (e.g. +1) more likely than large FCs (e.g. +2) 12 2 Example NH3 13 2 Formal Charge Formal charge = ve-’s – (lone pairs + bonds) In a neutral molecule, the sum of the FCs = zero. For an ion, the sum of the FCs = the charge of the ion. 14 2 Formal Charge –the easy way! 1. Circle the atom of interest. 2. Count the electrons inside the circle. If the circle “breaks” a bond, only count one electron of the bond. 3. Take the ve-’s for the atom (its group number) and subtract #2. FC of oxygen= 6 – (6) = 0 O C O FC of carbon= 4 – (4) = 0 15 2 Resonance Structures Resonance structures result when more than one valid Lewis dot structure can be drawn for one molecule. – The positions of the nuclei can’t change (C, H, etc.) – The positions of multiple bonds or lone pairs can move – Low FCs are still favored 16 2 Computing Formal Charges “Normal” covalent bonding patterns: Carbon Nitrogen Oxygen C N O C C C N N O Halogens X Onebond Threelonepairs Twobonds Twolonepairs Threebonds Onelonepair Four bonds Nolonepairs 17 2 Formal Charges Common Computing structures with formal charges: C a rb o n C N itro g e n O x y g e n O N H a lo g e n s X N C O N N N O N 18 3 Ionic versus Covalent Bonds formed by the transfer of electrons from one atom to another are __________. Example: Sodium chloride (NaCl) Na Na+ + eCl + e- Cl- __ Na + Cl NaCl + + + _ _ + + + _ _ + + + _ _ + + + 19 3 Bonds formed by the sharing of electrons between two atoms are __________. Example: Glucose (C6H12O6) 20 4 Polar Covalent Bonds Polar bonds are bonds between atoms created by sharing electrons unevenly. H F F F Uneven sharing is the result of electron “greedy” atoms (i.e. more electronegative atoms). 21 4 Electronegativity Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. Electronegativity differences result in polar covalent bonds.22 4 Polar Covalent Molecules A polar molecule is a molecule that is electrically asymmetrical, resulting in charges at two points. The molecule is said to have a molecular dipole or dipole moment. HC l O H H O C H C C H 3 3 23 4 Polar Covalent Molecules Not all molecules that contain polar bonds will be polar molecules! OCO 24 5 Molecular Geometry Common geometries: 25 PQ Acetone C3H6O Is acetone ionic or covalent? What its geometry? 26 5 Atomic orbitals (AOs)are the probability distribution about one atomic nucleus(found using wave functions ψ) AOs relate to quantum numbers (n, l, ml, ms) Each AO can have, at most, two e- (Pauli Exclusion Principle) AOs are filled with e-’s from the lowest energy to the highest (Aufbau Principle) The electron configuration with the highest number of unpaired spin is more stable (Hund’s rule) 27 5 Atom Electronic Structure Electronic Configuration LewisDot Structure 3p 3s Boron 2 2 1 1s 2s 2p 2p 2s B 1s 3p 3s Phosphorus 2 3 [Ne] 3s 3p 2p 2s P 1s 28 5 Scandium 29 Carbon AtomicNumber Number==66 Atomic 2p 2s 1s 30 5 Hybridized Orbitals 31 Hybridized Orbitals When carbon double bonds, the 2s, 2px and 2py orbitals on carbon form three sp2 hybrid orbitals. The three hybrid orbitals form the points of a triangle. C A trigonal planar atom has sp2 hybridization. 32 6 Double Bonds H H C H C H The three sp2 hybrid orbitals of carbon and 1s orbitals of hydrogen make up the σ-framework of ethene. 33 6 Double Bonds When the double bond is formed between the two carbons of ethene, a different type of bond is needed (a π bond). This bond is formed with the remaining 2pz orbitals and is higher energy than the σ bonds. 34