Note For Week 2
Note For Week 2 Chem 345
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This 4 page Class Notes was uploaded by Bethany Lawler on Friday August 28, 2015. The Class Notes belongs to Chem 345 at Washington State University taught by Dr. Crouch in Summer 2015. Since its upload, it has received 23 views. For similar materials see Organic Chemistry 1 in Chemistry at Washington State University.
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Date Created: 08/28/15
Chemistry 345 Week 2 831 94 1 Bonding When an atom such as carbon has empty orbitals that it wants to fill it will try and form bonds to form a bond the atom will form a hybrid orbital The new hybrid orbitals are named after the atomic orbitals that they are made up of in the case above the four hybrid orbitals would be called sp3 orbitals The new orbitals have a different shape than the atomic orbitals that make them up The s orbital will combine with the half of the p orbital that shares the same phase via constructive interference and make it bigger The p orbital of the opposite phase will be made smaller by destructive interference All molecular geometry is formed by orbital hybridization It is important to be able to recognize which hybrid orbitals go into forming a bond 2 Types of Bonds When two orbitals form a single bond this is called a sigma bond Sigma bonds have the ability to rotate about an internuclear axis When four orbitals form two bonds one is a sigma bond but the other is formed by a set of perpendicular orbitals These bonds are called pi bonds Pi bonds cannot rotate around an internuclear axis In triple bonds one of the bonds is a sigma bond The other two are pi bonds perpendicular to the sigma bond and 90 from each other 3 Hybrid orbitals and bonds Generally when neutral atoms form single bonds they do so with sp3 orbitals When they form double bonds they use sp2 orbitals When they form triple bonds they use sp orbitals 4 Strange Cases A carbocation which has a charge of 1 because it has lost an electron rather than forming a bond will form sp2 orbitals with the p orbital remaining empty A carbon that has a free radical will also form sp2 orbitals and the lone electron will populate the p orbital Methyl anion a carbon that has an extra electron to fill an orbital and a charge of 1 will have sp3 orbitals with a lone pair filling one 5 Hybridization for atoms with more valence electrons than carbon Nitrogen still forms sp3 orbitals the same as carbon but one of the hybridized orbitals is filled by valence electrons so nitrogen can only make three bonds If nitrogen is protonated four hydrogens are bonded to the nitrogen instead of three nitrogen gains a charge of 1 Oxygen also forms sp3 orbitals but two of the hybridized orbitals are filled by valence electrons so oxygen can only make two bonds 6 Bond Strength The smaller the distance between atoms shorter the bond the stronger the bond Sigma bonds are longer than pi bonds therefore they are weaker Pi bonds however are more reactive Triple bonds one sigma and two pi are stronger than double bonds one sigma one pi Therefore triple bonds are stronger than double bonds Triple bonds are stronger because they are formed with sp orbitals which have a great amount of s orbital in them than sp2 or sp3 orbitals The greater the amount of s character in a bond the stronger it will be The affects bond angle as well The more s character a bond has the larger the bond angles are Therefore the stronger the bond the larger the bond angles 7 Molecular Dipoles Molecules can have slightly positive and negative dipoles if they have polar bonds If the polar bonds are symmetrical and cancel each other out the overall molecule does not have a dipole If the polar bonds are not symmetrical and don t cancel each other out the overall molecule will have dipoles 8 BronstedLowry theory In the BronstedLowry model acids act as proton donators Bases act as proton acceptors 9 Reactionary arrows in a system at equilibrium If the arrows are the same size the solution has equal amounts of reactants and products at equilibrium If the arrow pointing to the products is larger then there is a larger amount of products then reactants at equilibrium If the arrow pointing to the reactants is larger then there is a larger amount of reactants than products at equilibrium 10 Conjugates After an acid donates its proton it turns into a conjugate base This means that it can now act as a proton acceptor After a base accepts a proton it turns into a conjugate acid This means that is can now act as a proton donator The stronger the original acid or base the weaker its conjugate 11 Strong acids and bases A strong acid will nearly completely disassociate in solution A weak acid will remain mostly unchanged in solution A strong base will have a large amount of OH in solution because it pulls a proton from water A weak base will have low concentrations of OH 0 Strong acids have pKa lt 1 0 Weak acids have pKa gt 1 12 Substances that act as both acids and bases 0 Water and alcohols act as both acids and bases because they have a proton on their OH functional groups to give up and the oxygen on the OH group will accept another proton 0 Amines act as both acids and bases because it has a proton it can donate from the amine functional group although it doesn39t prefer to and the nitrogen on the functional group will accept another proton 13 Determining relative equilibrium 0 Whichever substance reactant or product has the larger pKa will be the substance the equilibrium favors o The equilibrium favors the weaker acid 14 Stability of acids and bases 0 Weak bases are stable bases 0 Alcohols have a better ability to handle the extra charge associated with losing a proton than amines o The more stable the base the weaker it is and the stronger its conjugate acid 15 Substituents 0 Substituents increase the stability of a conjugate base which strengthens the associated acid 0 The effect of the substituent is dependent on its distance from a negatively charged functional group 0 The farther from the functional group the weaker the effect the closer the stronger 16 Proton bond strength in an acid 0 The stronger the bond between the proton and the acid molecule the weaker the acid 0 Longer bonds between the proton and acid molecule means a stronger acid 17 Resonance and base stability 0 Conjugate bases that have resonance structure to share the extra negative charge of losing a proton are more stable than those that don t 0 This makes the associated acid stronger 18 The effect of Ionization on solubility 0 An ionized particle is soluble in a polar substance such as water 0 If an unionized molecule is deprotonated or otherwise ionized it becomes soluble in polar substances such as water 0 Some unionized substances are more soluble in water than others because they are smaller 19 When the pH and pKa of a solution are equal exactly half the solution has been deprotonated 20 Affects Hybridization on acidity 0 When an orbital hybridized it has different amounts of s character depending on which orbitals hybridize 0 The more s character the orbital has the more stable it is when it gains a charge 0 Therefore an sp orbital is the most stable 0 The more stable the conjugate base the stronger the associated acid 21 Lewis acids and Bases 0 Lewis acids are molecules which accept an electron pair 0 Lewis bases are molecules which donate an electron pair 0 The main difference between Lewis acids and bases and BrowsedLowry acids and bases is that BrowsedLowry acids and bases must transfer protons which Lewis acids and bases do not
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