Chapter 6: Ionic Bonds and Some Main-Group Chemistry 4/8/2019 Copyright © 2008 Pearson Prentice Hall, Inc.

12.1 Types of Chemical Bonds Bonds: a force that holds groups of two or more atoms together and makes them function as a unit Required 2 e- to make a bond Bond energy: amount of energy required to form or to break the bond

Ionic Bonding Occurs in ionic compound Results from transferring electron Created a strong attraction among the closely pack compound

Ions and Their Electron Configurations Chapter 6: Ionic Bonds and Some Main-Group Chemistry 4/8/2019 Ions and Their Electron Configurations Atoms Ions N: O: F: Na: Mg: Al: 1s2 2s2 2p3 1s2 2s2 2p4 1s2 2s2 2p5 1s2 2s2 2p6 3s1 1s2 2s2 2p6 3s2 1s2 2s2 2p6 3s2 3p1 + 3 e- + 2 e- + 1 e- - 1 e- - 2 e- - 3 e- N3-: O2-: F1-: Ne: Na1+: Mg2+: Al3+: 1s2 2s2 2p6 Copyright © 2008 Pearson Prentice Hall, Inc.

Ions and Their Electron Configurations Chapter 6: Ionic Bonds and Some Main-Group Chemistry Ions and Their Electron Configurations 4/8/2019 Copyright © 2008 Pearson Prentice Hall, Inc.

Ions and Their Electron Configurations Chapter 6: Ionic Bonds and Some Main-Group Chemistry 4/8/2019 Ions and Their Electron Configurations Atoms Ions Fe: [Ar] 4s2 3d6 - 2 e- - 3 e- Fe2+: Fe3+: [Ar] 3d6 [Ar] 3d5 It’s not a simple reverse of the process when discussing ions. It’s the configuration of the ion that’s important to consider and the energy levels have a different arrangement in the ions. Copyright © 2008 Pearson Prentice Hall, Inc.

Chapter 6: Ionic Bonds and Some Main-Group Chemistry 4/8/2019 Ionic Radii Effective nuclear charge. Copyright © 2008 Pearson Prentice Hall, Inc.

Chapter 6: Ionic Bonds and Some Main-Group Chemistry 4/8/2019 Ionic Radii Effective nuclear charge. Copyright © 2008 Pearson Prentice Hall, Inc.

Chapter 6: Ionic Bonds and Some Main-Group Chemistry 4/8/2019 Ionization Energy Ionization Energy (Ei): The amount of energy necessary to remove the highest-energy electron from an isolated neutral atom in the gaseous state. Students sometimes mistakenly equate ionization energy to the amount of energy required to form an ion. Copyright © 2008 Pearson Prentice Hall, Inc.

Chapter 6: Ionic Bonds and Some Main-Group Chemistry Ionization Energy 4/8/2019 Note the periodicity of the first ionization energies. Copyright © 2008 Pearson Prentice Hall, Inc.

Chapter 6: Ionic Bonds and Some Main-Group Chemistry Ionization Energy 4/8/2019 Boron has a lower Ei due to a smaller Zeff (shielding by the 2s electrons) Copyright © 2008 Pearson Prentice Hall, Inc.

Chapter 6: Ionic Bonds and Some Main-Group Chemistry 4/8/2019 Ionization Energy Oxygen has a lower Ei since the first electron is removed from a filled orbital Copyright © 2008 Pearson Prentice Hall, Inc.

Higher Ionization Energies Chapter 6: Ionic Bonds and Some Main-Group Chemistry 4/8/2019 Higher Ionization Energies M1+ + e- M + energy M2+ + e- M1+ + energy M3+ + e- M2+ + energy Copyright © 2008 Pearson Prentice Hall, Inc.

Chapter 6: Ionic Bonds and Some Main-Group Chemistry 4/8/2019 Electron Affinity Electron Affinity (Eea): The energy released when a neutral atom gains an electron to form an anion. Books use different conventions. The one this book uses assigns a negative sign to electron affinity. Copyright © 2008 Pearson Prentice Hall, Inc.

Ionic Bonds and the Formation of Ionic Solids Chapter 6: Ionic Bonds and Some Main-Group Chemistry 4/8/2019 Ionic Bonds and the Formation of Ionic Solids 1s2 2s2 2p6 3s1 1s2 2s2 2p6 3s2 3p5 Na + Cl Na1+ Cl1- A transfer of electrons from the metal to the nonmetal. 1s2 2s2 2p6 1s2 2s2 2p6 3s2 3p6 Copyright © 2008 Pearson Prentice Hall, Inc.

Chapter 6: Ionic Bonds and Some Main-Group Chemistry 4/8/2019 Copyright © 2008 Pearson Prentice Hall, Inc.

Chapter 6: Ionic Bonds and Some Main-Group Chemistry 4/8/2019 The Octet Rule Octet Rule: Main-group elements tend to undergo reactions that leave them with eight outer-shell electrons. Copyright © 2008 Pearson Prentice Hall, Inc.

Chapter 6: Ionic Bonds and Some Main-Group Chemistry The Octet Rule 4/8/2019 Octet Rule: Main-group elements tend to undergo reactions that leave them with eight outer-shell electrons. Metals tend to have low Ei and low Eea. They tend to lose one or more electrons. Nonmetals tend to have high Ei and high Eea. They tend to gain one or more electrons. Copyright © 2008 Pearson Prentice Hall, Inc.

Chapter 6: Ionic Bonds and Some Main-Group Chemistry 4/8/2019 The Octet Rule This is important in Lewis structures and molecular shapes. Copyright © 2008 Pearson Prentice Hall, Inc.

Covalent Bond and Molecular Structure Chapter 7 Covalent Bond and Molecular Structure

Chapter 7: Covalent Bonds and Molecular Structure 4/8/2019 The Covalent Bond Covalent Bond: A bond that results from the sharing of electrons between atoms. Copyright © 2008 Pearson Prentice Hall, Inc.

Chapter 7: Covalent Bonds and Molecular Structure 4/8/2019 Copyright © 2008 Pearson Prentice Hall, Inc.

Polar Covalent Bonds: Electronegativity Chapter 7: Covalent Bonds and Molecular Structure 4/8/2019 Polar Covalent Bonds: Electronegativity Electronegativity: The ability of an atom in a molecule to attract the shared electrons in a covalent bond. Copyright © 2008 Pearson Prentice Hall, Inc.

Polar Covalent Bonds: Electronegativity Chapter 7: Covalent Bonds and Molecular Structure 4/8/2019 Polar Covalent Bonds: Electronegativity NaCl Cl2 HCl Copyright © 2008 Pearson Prentice Hall, Inc.

Polar Covalent Bonds: Electronegativity Chapter 7: Covalent Bonds and Molecular Structure 4/8/2019 Polar Covalent Bonds: Electronegativity Copyright © 2008 Pearson Prentice Hall, Inc.

Polarity Polar covalent bonds – the bonding electrons are attracted somewhat more strongly by one atom in a bond Electrons are not completely transferred More electronegative atom: δ- . (δ represents the partial negative charge formed) Less electronegative atom: δ+

Relationship Between Electronegativity and Bond Type Predicting bond polarity Atoms with similar electronegativity (Δ EN <0.4) –form nonpolar bond Atoms whose electronegativity differ by more than two (Δ EN > 2) – form ionic bonds Atoms whose electronegativity differ by less than two (Δ EN < 2) – form polar covalent bonds

Polarity and Dipole Moment a vector quantity from the center of the positive charge to the center of negative charge Represents with an arrow E.g Draw the dipole moment for HF, H2O, HCl, OF

Examples For each of the following pairs of bonds, choose the bond that will be more polar a. H-P, H-C b. N-O, S-O

Lewis Structures represents how an atom’s valence electrons are distributed in a molecule Show the bonding involves (the maximum bonds can be made) Try to achieve the noble gas configuration

Examples Draw Dot Lewis structure for the following atoms: Na Mg C S Co Copyright © 2008 Pearson Prentice Hall, Inc.

Rules Duet Rule: sharing of 2 electrons E.g H2 H : H Octet Rule: sharing of 8 electrons Carbon, oxygen, nitrogen and fluorine always obey this rule in a stable molecule E.g F2, O2 Bonding pair: two of which are shared with other atoms Lone pair or nonbonding pair: those that are not used for bonding

Electron-Dot Structures Chapter 7: Covalent Bonds and Molecular Structure 4/8/2019 Electron-Dot Structures Think of this section as an introduction. It is much easier to write electron-dot structures using the rules listed in the next section. Copyright © 2008 Pearson Prentice Hall, Inc.

Electron-Dot Structures Chapter 7: Covalent Bonds and Molecular Structure 4/8/2019 Electron-Dot Structures We have single, double, and triple bonds. Copyright © 2008 Pearson Prentice Hall, Inc.

Rules for Wring Dot Lewis structure Step 1: Calculate the total number of valence electrons of all atoms in the molecule Step 2: Create a skeletal structure using the following rules: Hydrogen atoms (if present) are always on the “outside” of the structure. They form only one bond The central atom is usually least electronegative. It is also often unique (i.e,. the only one atom of the element in the molecule). Remember, there might be no “central” atom. Connect bonded atoms by line (2-electron, covalent bonds

Rules Step 3: Place lone pairs around outer atoms (except hydrogen) so that each atom has an octet Step 4: Calculate the number of electrons you haven’t used. Subtract the number of electrons used so far, including electrons in lone pair and bonding pairs, from the total in Step 1. Assign any remaining electrons to the central atom as lone pair

Rules Step 5: If the central atom is B (boron) or Be (beryllium), skip this step If the central atom has an octet after step 4, skip this step If the central atom has only 6 electrons, move a lone pair from an outer atom to form a double bond between outer atom and the central atom If the central atom has only 4 electrons, do Step 5a to two different outer atoms (i.e, form two double bonds) or twice to one outer atom (i.e., form one triple bond)

Electron-Dot Structures of Polyatomic Molecules Chapter 7: Covalent Bonds and Molecular Structure 4/8/2019 Electron-Dot Structures of Polyatomic Molecules Draw an electron-dot structure for CF4. Step 1: Total valence electrons Step 2: Draw its skeletal Step 2: The positioning of the terminal atoms about the central is not critical as long as they simply surround the central atom. Step 3: The terminal atom is hydrogen. Step 5: The central atom has an octet so no multiple bonding. Step 4: Dot Lewis structure Copyright © 2008 Pearson Prentice Hall, Inc.

Examples Give the Lewis structure for the following H2O ClO4- CO2 NH3 NO3-,