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Dr. Wolf's CHM 201 & 202 1- 1 Chapter 1 Structure Determines Properties

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Dr. Wolf's CHM 201 & 202 1- 2 1.1 Atoms, Electrons, and Orbitals

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Dr. Wolf's CHM 201 & 202 1- 3 Protons positively charged mass = 1.6726 X 10 -27 kg Neutronsneutral mass = 1.6750 X 10 -27 kg Electrons negatively charged mass = 9.1096 X 10 -31 kg + – Atoms are composed of

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Dr. Wolf's CHM 201 & 202 1- 4 Atomic number (Z) = number of protons in nucleus (this must also equal the number of electrons in neutral atom) Mass number (A) = sum of number of protons + neutrons in nucleus X ZA Atomic Number and Mass Number

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Dr. Wolf's CHM 201 & 202 1- 5 Schrödinger combined the idea that an electron has wave properties with classical equations of wave motion to give a wave equation for the energy of an electron in an atom. Wave equation (Schrödinger equation) gives a series of solutions called wave functions ( ). Schrödinger Equation

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Dr. Wolf's CHM 201 & 202 1- 6 Only certain values of are allowed. Each corresponds to a certain energy. The probability of finding an electron at a particular point with respect to the nucleus is given by 2 The probability of finding an electron at a particular point with respect to the nucleus is given by 2. Each energy state corresponds to an orbital. Wave Functions

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Dr. Wolf's CHM 201 & 202 1- 7 Figure 1.1 Probability distribution ( 2 ) for an electron in a 1s orbital.

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Dr. Wolf's CHM 201 & 202 1- 8 Figure 1.2 Boundary surfaces of a 1s orbital and a 2s orbital. 1s2s A boundary surface encloses the region where the probability of finding an electron is high—on the order of 90-95%

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Dr. Wolf's CHM 201 & 202 1- 9 Each orbital is characterized by a unique set of four quantum numbers. The principal quantum number (n) is a whole number (integer, 1, 2, etc.) that specifies the shell and is related to the energy of the orbital. The angular momentum quantum number (l) is usually designated by a letter (s, p, d, f, etc) and describes the shape of the orbital. Values for l range from 0 to (n-1) Quantum Numbers

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Dr. Wolf's CHM 201 & 202 1- 10 Each orbital is characterized by a unique set of four quantum numbers. The magnetic quantum number m is a whole number ranging from –l through 0 to +l. This gives the orientation of the orbital. The spin quantum number is either + or - ½ for the electron spin clockwise or counter clockwise Quantum Numbers

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Dr. Wolf's CHM 201 & 202 1- 11 s Orbitals are spherically symmetric. The energy of an s orbital increases with the number of nodal surfaces it has. A nodal surface is a region where the probability of finding an electron is zero. A 1s orbital has no nodes; a 2s orbital has one; a 3s orbital has two, etc. s Orbitals

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Dr. Wolf's CHM 201 & 202 1- 12 No two electrons in the same atom can have the same set of four quantum numbers. Two electrons can occupy the same orbital only when they have opposite spins. There is a maximum of two electrons per orbital. The Pauli Exclusion Principle

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Dr. Wolf's CHM 201 & 202 1- 13 1s1s1s1s 2s2s2s2s 2p2p2p2pH He Principal quantum number (n) = 1 HydrogenHelium Z = 1Z = 2 1s 1 1s 2 First Period

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Dr. Wolf's CHM 201 & 202 1- 14 p Orbitals are shaped like dumbells. Are not possible for n = 1. Are possible for n = 2 and higher. p Orbitals

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Dr. Wolf's CHM 201 & 202 1- 15 p Orbitals are shaped like dumbells. Are not possible for n = 1. Are possible for n = 2 and higher. There are three p orbitals for each value of n (when n is greater than 1). p Orbitals

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Dr. Wolf's CHM 201 & 202 1- 16 p Orbitals are shaped like dumbells. Are not possible for n = 1. Are possible for n = 2 and higher. There are three p orbitals for each value of n (when n is greater than 1). p Orbitals

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Dr. Wolf's CHM 201 & 202 1- 17 p Orbitals are shaped like dumbells. Are not possible for n = 1. Are possible for n = 2 and higher. There are three p orbitals for each value of n (when n is greater than 1). p Orbitals

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Dr. Wolf's CHM 201 & 202 1- 18 Principal quantum number (n) = 2 1s1s1s1s 2s2s2s2s 2p2p2p2p Be 4 B 5 C 6 Li 3 Z Second Period

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Dr. Wolf's CHM 201 & 202 1- 19 1s1s1s1s 2s2s2s2s 2p2p2p2p O 8 F 9 Ne 10 N 7 Z Second Period

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Dr. Wolf's CHM 201 & 202 1- 20 1.2 Ionic Bonds

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Dr. Wolf's CHM 201 & 202 1- 21 An ionic bond is the force of electrostatic attraction between oppositely charged ions Cl – (anion) Na + (cation) Ionic Bonding

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Dr. Wolf's CHM 201 & 202 1- 22 Ionic bonds are common in inorganic chemistry but rare in organic chemistry. Carbon shows less of a tendency to form cations than metals do, and less of a tendency to form anions than nonmetals. Ionic Bonding

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Dr. Wolf's CHM 201 & 202 1- 23 1.3 Covalent Bonds and the Octet Rule

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Dr. Wolf's CHM 201 & 202 1- 24 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. An electron pair that is shared between two atoms constitutes a covalent bond. The Lewis Model of Chemical Bonding

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Dr. Wolf's CHM 201 & 202 1- 25 Covalent Bonding in H 2 H.H. Two hydrogen atoms, each with 1 electron, can share those electrons in a covalent bond. H:H Sharing the electron pair gives each hydrogen an electron configuration analogous to helium.

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Dr. Wolf's CHM 201 & 202 1- 26 Covalent Bonding in F 2 Two fluorine atoms, each with 7 valence electrons, can share those electrons in a covalent bond. Sharing the electron pair gives each fluorine an electron configuration analogous to neon..... F.F.: :.... F : F : :........

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Dr. Wolf's CHM 201 & 202 1- 27 The Octet Rule The octet rule is the most useful in cases involving covalent bonds to C, N, O, and F. F : F : :........ In forming compounds, atoms gain, lose, or share electrons to give a stable electron configuration characterized by 8 valence electrons.

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Dr. Wolf's CHM 201 & 202 1- 28 C.... F :..... Combine carbon (4 valence electrons) and four fluorines (7 valence electrons each) to write a Lewis structure for CF 4. : F :.... C : F :.... : F :.... : F :.... The octet rule is satisfied for carbon and each fluorine. ExampleExample

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Dr. Wolf's CHM 201 & 202 1- 29 It is common practice to represent a covalent bond by a line. We can rewrite : F :.... C : F :.... : F :.... : F :...... C F F F F........ : : : :::.. as ExampleExample

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Dr. Wolf's CHM 201 & 202 1- 30 1.4 Double Bonds and Triple Bonds

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Dr. Wolf's CHM 201 & 202 1- 31 C : : : O.. : O..: : C : O.. O..: :::N : C : H :NC H Carbon dioxide Hydrogen cyanide Inorganic Examples

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Dr. Wolf's CHM 201 & 202 1- 32 Ethylene Acetylene :::C : C : H H CC HH C : : C.. H ::.. H HH C CHHH H Organic Examples

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Dr. Wolf's CHM 201 & 202 1- 33 1.5 Polar Covalent Bonds and Electronegativity

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Dr. Wolf's CHM 201 & 202 1- 34 An electronegative element attracts electrons. An electropositive element releases electrons. ElectronegativityElectronegativity Electronegativity is a measure of the ability of an element to attract electrons toward itself when bonded to another element.

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Dr. Wolf's CHM 201 & 202 1- 35 Electronegativity increases from left to right in the periodic table. Electronegativity decreases going down a group. Electronegativity increases from left to right in the periodic table. Electronegativity decreases going down a group. Pauling Electronegativity Scale

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Dr. Wolf's CHM 201 & 202 1- 36 The greater the difference in electronegativity between two bonded atoms; the more polar the bond. GeneralizationGeneralization nonpolar bonds connect atoms of the same electronegativity H—H : N N: F :.... F :....

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Dr. Wolf's CHM 201 & 202 1- 37 The greater the difference in electronegativity between two bonded atoms; the more polar the bond. GeneralizationGeneralization polar bonds connect atoms of different electronegativity : O C F :.... H O.... H H O :....

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Dr. Wolf's CHM 201 & 202 1- 38 Electrostatic potential maps show the charge distribution within a molecule. Electrostatic Potential Maps Red is negative charge; blue is positive. F :.... H Solid surface

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Dr. Wolf's CHM 201 & 202 1- 39 Electrostatic potential maps show the charge distribution within a molecule. Electrostatic Potential Maps Red is negative charge; blue is positive. F :.... H Transparent surface

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Dr. Wolf's CHM 201 & 202 1- 40 Electrostatic potential maps show the charge distribution within a molecule. Electrostatic Potential Maps Red is negative charge; blue is positive. F :.... H Li H

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Dr. Wolf's CHM 201 & 202 1- 41 1.6 Formal Charge Formal charge is the charge calculated for an atom in a Lewis structure on the basis of an equal sharing of bonded electron pairs.

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Dr. Wolf's CHM 201 & 202 1- 42 Nitric acid.. :.. H O O O N : :.... We will calculate the formal charge for each atom in this Lewis structure. Formal charge of H

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Dr. Wolf's CHM 201 & 202 1- 43 Nitric acid.. :.. H O O O N : :.... Hydrogen shares 2 electrons with oxygen.Hydrogen shares 2 electrons with oxygen. Assign 1 electron to H and 1 to O.Assign 1 electron to H and 1 to O. A neutral hydrogen atom has 1 electron.A neutral hydrogen atom has 1 electron. Therefore, the formal charge of H in nitric acid is 0.Therefore, the formal charge of H in nitric acid is 0. Formal charge of H

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Dr. Wolf's CHM 201 & 202 1- 44 Nitric acid.. :.. H O O O N : :.... Oxygen has 4 electrons in covalent bonds.Oxygen has 4 electrons in covalent bonds. Assign 2 of these 4 electrons to O.Assign 2 of these 4 electrons to O. Oxygen has 2 unshared pairs. Assign all 4 of these electrons to O.Oxygen has 2 unshared pairs. Assign all 4 of these electrons to O. Therefore, the total number of electrons assigned to O is 2 + 4 = 6.Therefore, the total number of electrons assigned to O is 2 + 4 = 6. Formal charge of O

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Dr. Wolf's CHM 201 & 202 1- 45 Nitric acid.. :.. H O O O N : :.... Electron count of O is 6.Electron count of O is 6. A neutral oxygen has 6 electrons.A neutral oxygen has 6 electrons. Therefore, the formal charge of O is 0.Therefore, the formal charge of O is 0. Formal charge of O

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Dr. Wolf's CHM 201 & 202 1- 46 Nitric acid.. :.. H O O O N : :.... Electron count of O is 6 (4 electrons from unshared pairs + half of 4 bonded electrons).Electron count of O is 6 (4 electrons from unshared pairs + half of 4 bonded electrons). A neutral oxygen has 6 electrons.A neutral oxygen has 6 electrons. Therefore, the formal charge of O is 0.Therefore, the formal charge of O is 0. Formal charge of O

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Dr. Wolf's CHM 201 & 202 1- 47 Nitric acid.. :.. H O O O N : :.... Electron count of O is 7 (6 electrons from unshared pairs + half of 2 bonded electrons).Electron count of O is 7 (6 electrons from unshared pairs + half of 2 bonded electrons). A neutral oxygen has 6 electrons.A neutral oxygen has 6 electrons. Therefore, the formal charge of O is -1.Therefore, the formal charge of O is -1. Formal charge of O

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Dr. Wolf's CHM 201 & 202 1- 48 Nitric acid.. :.. H O O O N : :.... Electron count of N is 4 (half of 8 electrons in covalent bonds).Electron count of N is 4 (half of 8 electrons in covalent bonds). A neutral nitrogen has 5 electrons.A neutral nitrogen has 5 electrons. Therefore, the formal charge of N is +1.Therefore, the formal charge of N is +1. Formal charge of N –

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Dr. Wolf's CHM 201 & 202 1- 49 Nitric acid.. :.. H O O O N : :.... A Lewis structure is not complete unless formal charges (if any) are shown.A Lewis structure is not complete unless formal charges (if any) are shown. Formal charges – +

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Dr. Wolf's CHM 201 & 202 1- 50 Formal charge = group number in periodic table number of bonds number of unshared electrons –– An arithmetic formula for calculating formal charge. Formal Charge

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Dr. Wolf's CHM 201 & 202 1- 51 "Electron counts" and formal charges in NH 4 + and BF 4 - 1 4 N H H H H + 7 4..B F F F F........ : : : : : :.. – Formal Charge

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