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 Living Things Study of Carbon Compounds (C,H,N,O) Matter Derived From Nonliving Things Vast Majority of the Periodic Table 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: 1 st 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.Atomic Structure 2.Lewis Dot Structures and Formal Charge 3.Ionic and Covalent Bonds 4.Electronegativity and Polarity 5.Molecular Geometry 6.Multiple Bonds 5

Modern Atomic Theory Atoms have an internal structure consisting of one or more subatomic particles: 1 6

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 1 7

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? 1 8

Valence and Core Electrons Electrons contained in the outermost shell are called ________electrons. All other electrons are called ______ electrons. e- How many valence electrons does this atom have? Core electrons? Which number matters more? 1 9

How many valence electrons (ve-’s) does carbon have? Calcium? What element is depicted in the image on the right? 1 10

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 OOC 2 11

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) 2 12

Example NH

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. 2 14

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. OOC FC of oxygen= 6 – (6) = 0 FC of carbon= 4 – (4) =

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 2 16

Computing Formal Charges “Normal” covalent bonding patterns: 2 17

Computing Formal Charges Common structures with formal charges: 2 18

Ionic versus Covalent Bonds formed by the transfer of electrons from one atom to another are __________. Example: Sodium chloride (NaCl) Na  Na + + e - Cl + e -  Cl - __ Na + Cl  NaCl ___ ___ 3 19

Bonds formed by the sharing of electrons between two atoms are __________. Example: Glucose (C 6 H 12 O 6 ) 3 20

Polar Covalent Bonds Polar bonds are bonds between atoms created by sharing electrons unevenly. Uneven sharing is the result of electron “greedy” atoms (i.e. more electronegative atoms). 4 21

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. 4 22

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. 4 23

Polar Covalent Molecules Not all molecules that contain polar bonds will be polar molecules! 4 24

Molecular Geometry Common geometries: 5 25

Acetone C 3 H 6 O Is acetone ionic or covalent? What its geometry? PQ 26

Atomic orbitals (AOs)are the probability distribution about one atomic nucleus (found using wave functions ψ) AOs relate to quantum numbers (n, l, m l, m s ) 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) 5 27

5 28

Scandium 5 29

Carbon Atomic Number = 6 30

Hybridized Orbitals 5 31

Hybridized Orbitals When carbon double bonds, the 2s, 2p x and 2p y orbitals on carbon form three sp 2 hybrid orbitals. C A trigonal planar atom has sp 2 hybridization. The three hybrid orbitals form the points of a triangle. 32

Double Bonds C C H H H H The three sp2 hybrid orbitals of carbon and 1s orbitals of hydrogen make up the σ-framework of ethene. 6 33

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 2p z orbitals and is higher energy than the σ bonds. 6 34