Chapter 6: Ionic Bonds and Some Main-Group Chemistry 1/2/2019 Copyright © 2008 Pearson Prentice Hall, Inc.

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

Ions and their configuration Mg Mg2+ O O2- Atoms Ions Fe: [Ar] 4s2 3d6 - 2 e- - 3 e- Fe2+: Fe3+: [Ar] 3d6 [Ar] 3d5 Mn: Mn2+

Chapter 6: Ionic Bonds and Some Main-Group Chemistry 1/2/2019 Ionic Radii Effective nuclear charge. Copyright © 2008 Pearson Prentice Hall, Inc.

Chapter 6: Ionic Bonds and Some Main-Group Chemistry Ionization Energy 1/2/2019 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. Increasing Ei Decreasing Ei Copyright © 2008 Pearson Prentice Hall, Inc.

Chapter 6: Ionic Bonds and Some Main-Group Chemistry Ionization Energy 1/2/2019 Boron has a lower Ei due to a smaller Zeff (shielding by the 2s electrons) 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 1/2/2019 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 Ionic Bonds and the Formation of Ionic Solids 1/2/2019 1s2 2s2 2p63s1 1s2 2s2 2p6 3s23p5 Na + Cl Na1+ Cl1- 1s2 2s2 2p6 1s2 2s2 2p6 3s2 3p6 A transfer of electrons from the metal to the nonmetal. Copyright © 2008 Pearson Prentice Hall, Inc.

Chapter 6: Ionic Bonds and Some Main-Group Chemistry 1/2/2019 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 1/2/2019 The Octet Rule This is important in Lewis structures and molecular shapes. Copyright © 2008 Pearson Prentice Hall, Inc.

Chapter 7 Covalent Bond and Molecular Structure

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

Chapter 7: Covalent Bonds and Molecular Structure 1/2/2019 The Covalent Bond Covalent Bond: A bond that results from the sharing of electrons between atoms. Copyright © 2008 Pearson Prentice Hall, Inc.

Polar Covalent Bonds: Electronegativity Chapter 7: Covalent Bonds and Molecular Structure 1/2/2019 Polar Covalent Bonds: Electronegativity Depending on the relative electronegativities of the two atoms sharing electrons, there may be partial transfer of electron density from one atom to the other. When the electronegativities are not equal, electrons are not shared equally and partial ionic charges develop. Atoms with greater electronegativities will attract more of the shared electron density to themselves, causing a “polarity” to the bond Electronegativity is a measure of the ability of an atom in a molecule to draw bonding electrons density to itself. Copyright © 2008 Pearson Prentice Hall, Inc.

Polar Covalent Bonds: Electronegativity Chapter 7: Covalent Bonds and Molecular Structure Polar Covalent Bonds: Electronegativity 1/2/2019 NaCl Cl2 NaCl HCl Copyright © 2008 Pearson Prentice Hall, Inc.

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 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+ Example: 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 or Lewis Formula 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 The common pattern

Examples Draw Dot Lewis structure for the following atoms: Na Mg C S Co

Rules for multiple atoms 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 1/2/2019 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.

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 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 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)

Examples Give the Lewis structure for the following HBr CO2 BH3 OF2 NH4+ NO3-,

Resonance when there is more than one Lewis structure for a molecule that differ only in the position of the electrons, they are called resonance structures the actual molecule is a combination of the resonance forms – a resonance hybrid it does not resonate between the two forms, though we often draw it that way look for multiple bonds or lone pairs Rules for drawing resonance Resonance structures must have the same connectivity only electron positions can change Resonance structures must have the same number of electrons Second row elements have a maximum of 8 electrons bonding and nonbonding third row can have expanded octet Formal charges must total same Better structures have fewer formal charges Better structures have smaller formal charges

Complete the three resonance formulas below by using all correct arrows pushing. The draw a resonance hybrid