Chapter 01 Covalent Bonding and Shapes of Molecules. Atomic Structure. Chapter 01 Topics. Structure. Atomic Structure. Subatomic Particles

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1 hapter 01 ovalent Bonding and Shapes of Molecules EM 240: Fall 2016 Prof. Greg ook hapter 01 Topics Mostly a review of general chemistry Atomic Structure Lewis Models and Bonding Bonding and Shapes of Molecules Resonance ovalent Bonding and ybridization 2 Structure The sequence of connections that defines a molecule, including the spatial orientation of these connections Atomic Structure 3 Subatomic Particles Atomic Structure Nucleus is made up of Protons and Neutrons mass of Proton = x kg mass of Neutron = x kg Surrounding the Nucleus are electrons mass of Electron = x kg << proton 5 6

2 Atomic Structure Atomic Structure Atomic Structure Atomic Structure + - Electrons surround nucleus in orbitals Atomic Number (Z) = # protons in nucleus Mass Number (A) = # protons + # neutrons Atomic Weight = average mass of a large number of atoms + - A Z X Wave Function eisenberg uncertainty principle Electrons have properties of both Particles and Waves Quantum Mechanics help us understand the structure and behavior of electrons Schrödinger Wave Equation Describes the energy of an electron in an atom Wave functions ψ (psi) + We can t tell exactly where an electron is but we can tell where it will most likely be Probability of finding an electron at a particular spot relative to the nucleus is given by ψ 2 (psi)

3 rbitals Quantum Numbers Wave functions are also called orbitals each orbital characterized by 3 quantum numbers n : principle quantum number l : angular momentum quantum number ml : magnetic quantum number principle quantum number n an integer determines major part of orbital energy - the shell s orbitals Quantum Numbers s orbitals are spherical in shape energy increases with n Angular momemtum l determines the shape of the orbital for a given value of n : l = 0, 1, 2,,, n - 1 l = 0 : s l = 1: p l = 2 : d l = 3 : f p rbitals 4 th Quantum Number - Spin p orbitals are shaped like dumbells with a node in between the lobes (n = 2 and higher) Three orbitals with the same energy Each electron also has a spin quantum number ms +½ and -½ Pauli Exclusion Principle - two electrons may occupy the same orbital only when they have opposite or paired spins. No orbital can contain more than 2 electrons, e, Li 14 15

Electron onfiguration Periodic Table - Periods 16 17 Periodic Table - Periods Periodic Table - Periods

4 Electron onfiguration Periodic Table - Periods Periodic Table - Periods Periodic Table - Periods Periodic Table - Periods Second Period Electron onfigurations Z 1s 2s 2p Li 3 6 N 7 8 Ne

5 Second Period Electron onfigurations Z 1s 2s 2p Second Period Electron onfigurations Z 1s 2s 2p Li 3 Li N 7 8 N 7 8 Ne 10 Ne Ions Bonding 1s 2 2s 2 2p 6 3s 1 1s 2 2s 2 2p 6 3s 2 3p 5 21 Ionization Ionization 1s 2 2s 1 1s 2 2s 2 2p 5 Na l 1s 2 2s 0 1s 2 2s 2 2p 6 Na + - l 22 23

Ionic Bond An ionic bond is a force of attraction between oppositely charged species (ions). Ionic bonds are common in inorganic compounds but are more rare in organic compounds.

6 Ionic Bond An ionic bond is a force of attraction between oppositely charged species (ions). Ionic bonds are common in inorganic compounds but are more rare in organic compounds. Na + - l Ionic Bond An ionic bond is a force of attraction between oppositely charged species (ions). Ionic bonds are common in inorganic compounds but are more rare in organic compounds. Na + - l Ionization Ionization 1s 2 2s 2 2p 2 1s 2 2s 2 2p 6 3s 1 1s 2 2s 2 2p 6 3s 2 3p 5 1s 2 2s 2 2p 6 3s 1 1s 2 2s 2 2p 6 3s 2 3p ovalent Bonds ovalent Bonding in 2 In 1916 G. N. Lewis proposed that atoms combine in order to achieve a more stable electron configuration. Maximum stability results when an atom is isoelectronic with a noble gas. 1s 2 2s 0 e 1s 2 2s 2 2p 6 Ne Na + - l Two hydrogen atoms each have one electron Instead of ionizing, they come together to share both electrons between them An electron pair that is shared between two atoms constitutes a covalent bond. Sharing the electron pair allows both hydrogen atoms to have a filled orbital 26 27

7 ovalent Bonding in F2 ctet Rule Two fluorine atoms each have 7 valence electrons F F When forming compounds, atoms will gain, lose or share electrons to give a stable electron configuration characterized by 8 valence electrons F F They can share them in a covalent bond F F The octet rule is most useful in cases involving covalent bonds to, N, and F Each fluorine atom has the same electron configuration as Ne (8 electrons) Example with F4 Example with F4 arbon has 4 valence electrons, F has 7 F It is more common to represent a covalent bond (shared pair of electrons) with a line The Lewis structure for F4 F F F F F F F F = F F F F Example with F4 It is more common to represent a covalent bond (shared pair of electrons) with a line Example with F4 We often don t write the lone pairs (Kekulé structures) F F F F = F F F F F F F F You should know how many lone pairs an atom should have! 31 32

8 Structure Representation Lewis Dot Structures - all electrons are represented by dots around the atoms Kekulé Structures - atoms are drawn and lines represent shared electrons (covalent bonds) Structure Representation ondensed Structure - No bonds are shown and side groups are attached to the carbon before it 3 ( 3 ) 2 l 3 ondensed Structure 2-chloro-4-methylpentane ondensed Kekulé Structures l Kekulé Structure 2 3 ondensed Kekulé Structure 3 3 l Structure Representation Line Structure Examples Skeletal Line Structure - arbons and ydrogens are not shown. Each end of a line and intersection between lines represent a carbon atom. All other atoms are drawn. Br = = Br l Line Structure = 3 3 hydrocortisone beta carotene Methane Structure ybrid rbitals - Molecular Shapes bond length 1.1Å (110 pm) 38

9 VSEPR ybridization in Water? Valence Shell Electron Pair Repulsion - The electron repulsion between bonds and lone pairs sp 3 ybridization sp 3 ybridization arbon with 4 valence electrons atomic electron configuration p s sp 3 ybridization Bonding in Methane sp 3 ybrid electron configuration sp

10 Bonding in Methane Bonding in Ethane Structures of Methane, Ethane and Propane Double and Triple Bonds N N rganic Examples sp2 ybridization arbon with 4 valence electrons atomic electron configuration Ethylene (Ethene) Acetylene (Ethyne) p s sp 2 ybrid electron configuration sp 2 p 47 48

Alkenes ompounds that contain double bonds.

Ethylene (Ethene) 49 50 Structure of Alkynes sp ybridization arbon

ybrid electron configuration sp p 51 52 Electronegativity Polar

atoms in a covalent bond Electronegativity is a measure of the

bonded to another element An electronegative element attracts

11 Alkenes ompounds that contain double bonds. Structure and Bonding A double bond is sp 2 hybridized (pi bond) Ethylene (Ethene) Structure of Alkynes sp ybridization arbon with 4 valence electrons atomic electron configuration p s sp ybrid electron configuration sp p Electronegativity Polar ovalent Bonds Electrons are not always shared equally between atoms in a covalent bond Electronegativity is a measure of the ability of an element to attract electrons toward itself when bonded to another element An electronegative element attracts electrons gathering negative charge An electropositive element releases electrons gathering a positive charge 54

Pauling Electronegativity Scale Electronegativity Increases from left to right and bottom to top (decreases going down a group) 55 56 EN

atoms with the same EN Polar ovalent Bonds connect atoms that have different EN δ+ δ- δ+ δ- δ+ δ- δ+ δ- F l l partial negative charges on

Polar vs Ionic Bonds Electrostatic potential maps show the charge distribution within a molecule δ+ δ- inductive effect - the shifting of

12 Pauling Electronegativity Scale Electronegativity Increases from left to right and bottom to top (decreases going down a group) EN Generality Polar ovalent Bonds The greater the difference in EN between two bonded atoms, the more polar the bond Nonpolar bonds connect atoms with the same EN Polar ovalent Bonds connect atoms that have different EN δ+ δ- δ+ δ- δ+ δ- δ+ δ- F l l partial negative charges on atoms with higher EN and partial positive charges on atoms with lower EN Bond dipoles pointing from + toward Polar ovalent Bonds Polar vs Ionic Bonds Electrostatic potential maps show the charge distribution within a molecule δ+ δ- inductive effect - the shifting of electrons in a sigma bond in response to electronegative atoms nearby. F δ+ δ- A A A B A B ovalent polar covalent δen >2 INI BNDS δen <2 VALENT BNDS Ionic 59 60

13 Delocalization of Anion Spreading out charge is a stabilizing affect - through pi-bonds Resonance 62 Delocalization of Anion Delocalization of Anion Spreading out charge is a stabilizing affect - resonance has a large affect on acidity Delocalization of Anion More examples of resonance

14 Arrows are not Arrows In chemistry we use different kinds of arrows to indicate different things Reaction Arrow A B urved Arrows urved arrows are used to track the flow of electrons in chemical reactions Arrows begin where the electrons were originally and points to where they end up Equilibrium Arrow A B A B A + B Resonance Arrow A B A B A + B Dissociation and ombination urved arrows can be used in a variety of situations 3 + Br Functional Groups + l 68 Functional Groups Reactive parts of a molecule that undergo chemical reactions Functional Groups Alcohols, Amines, Aldehydes, Ketones, arboxylic Acids and derivatives 70 71

Chapter 1 Chemical Bonding

Chapter 1 Chemical Bonding 1.1 Atoms, Electrons, and Orbitals Atoms are composed of + Protons positively charged mass = 1.6726 X 10-27 kg Neutrons neutral mass = 1.6750 X 10-27 kg Electrons negatively