Basic Chemistry Copyright © 2011 Pearson Education, Inc. 1 Chapter 10 Structures of Solids and Liquids 10.1 Electron-Dot Formulas Sodium chlorite is used in the processing and bleaching of pulp from wood fibers and recycled cardboard.

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 2 Electron-Dot Symbols Electron-dot symbols show the valence electrons of an atom one to four valence electrons as single dots on the sides of an atomic symbol Five to eight valence electrons with one or more pairs of dots on the sides of an atomic symbol

Basic Chemistry Copyright © 2011 Pearson Education, Inc. Valence Electrons in Some Electron-Dot Symbols 3

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 4 Electron-Dot Formulas Electron-dot formulas show the sequence of bonded atoms in a molecule or polyatomic ion the bonding pairs of electrons shared between atoms the nonbonding or unshared (lone pairs) of valence electrons atoms with octets except H, which needs two electrons

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 8 I want you to meet a friend of mine? Bonding, the way atoms are attracted to each other to form molecules, determines nearly all of the chemical properties we see. And, as we shall see, the number “8” is very important to chemical bonding.

Basic Chemistry Copyright © 2011 Pearson Education, Inc. Copyright © Cengage Learning. All rights reserved 6 Questions to Consider What is meant by the term “chemical bond”? Why do atoms bond with each other to form compounds? How do atoms bond with each other to form compounds?

Basic Chemistry Copyright © 2011 Pearson Education, Inc. Copyright © Cengage Learning. All rights reserved 7 A Chemical Bond No simple, and yet complete, way to define this. Forces that hold groups of atoms together and make them function as a unit. A bond will form if the energy of the aggregate is lower than that of the separated atoms. Bond energy – energy required to break a chemical bond

Basic Chemistry Copyright © 2011 Pearson Education, Inc. Copyright © Cengage Learning. All rights reserved 8 Ionic Bonding Ionic compound results when a metal reacts with a nonmetal. Electrons are transferred.

Basic Chemistry Copyright © 2011 Pearson Education, Inc. Copyright © Cengage Learning. All rights reserved 9 Covalent Bonding A covalent bond results when electrons are shared by nuclei.

Basic Chemistry Copyright © 2011 Pearson Education, Inc. Copyright © Cengage Learning. All rights reserved 10 Polar Covalent Bond Unequal sharing of electrons between atoms in a molecule. One atom attracts the electrons more than the other atom. Results in a charge separation in the bond (partial positive and partial negative charge).

Basic Chemistry Copyright © 2011 Pearson Education, Inc. Copyright © Cengage Learning. All rights reserved 11 Concept Check What is meant by the term “chemical bond?” Why do atoms bond with each other to form molecules? How do atoms bond with each other to form molecules?

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 12 Drawing Electron-Dot Formulas

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 13 Example of Writing an Electron- Dot Formula for SF 2 Write the electron-dot formula for SF 2. STEP 1 Determine the arrangement of atoms. S is the central atom. F S F STEP 2 Determine the total number of valence electrons. 1 S(6 e  ) + 2 F(7 e  ) = 6 e  + 14 e  = 20 e 

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 14 Electron-Dot Formula for SF 2 STEP 3 Attach each bonded atom to the central atom with a pair of electrons. F : S : F STEP 4 Place the remaining electrons using single or multiple bonds to complete octets. Calculate the remaining electrons: 20 valence e  - 4 bonding e  = 16 e  remaining             : F : S : F : or : F─S─F :            

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 15 Learning Check Write the electron-dot formula for ClO 3 −.

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 16 Solution STEP 1 Determine the arrangement of atoms. Cl is the central atom. O − O Cl O STEP 2 Determine the total number of valence electrons. Include 1 e  for the negative charge on the ion. 3 O(6 e  ) + 1 Cl(7 e  ) + 1 e  = 18 e  + 7 e  + 1 e  = 26 e 

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 17 Solution (continued) STEP 3 Attach each bonded atom to the central atom with a pair of electrons. O −  O : Cl : O

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 18 Solution (continued) STEP 4 Place the remaining electrons using single or multiple bonds to complete octets. Calculate the remaining electrons: 26 valence e  - 6 bonding e  = 20 e  remaining   −    : O : : O :         │   : O : Cl : O : or : O─Cl─O :            

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 19 Multiple Bonds In a single bond, one pair of electrons is shared In a double bond, two pairs of electrons are shared In a triple bond, three pairs of electrons are shared

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 20 Multiple Bonds in N 2 In nitrogen, N 2, octets are achieved by sharing three pairs of electrons, which is a triple bond

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 21 Example of Writing the Electron-Dot Formula of CS 2 Write the electron-dot formula for CS 2. STEP 1 Determine the arrangement of atoms. The C atom is the central atom. S C S STEP 2 Determine the total number of valence electrons. 1 C(4 e  ) + 2 S(6 e  ) = 4 e  + 12 e = 16 e 

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 22 Electron-Dot Formula of CS 2 STEP 3 Attach each bonded atom to the central atom with a pair of electrons. S : C : S

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 23 Electron-Dot Formula of CS 2 STEP 4 Place the remaining electrons using single or multiple bonds to complete octets. Calculate the remaining electrons. 16 valence e  - 4 bonding e  = 12 e  remaining.... : S : C : S :.... To complete octets, move two lone pairs between C and each S atom to give two double bonds : S : : C : : S : or : S = C = S :

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 24 Resonance structures may be written for molecules or polyatomic ions with multiple bonds consist of two or more electron-dot formulas for the same arrangement of atoms are shown with a double-headed arrow are written by changing location of a double bond from the central atom to a different attached atom Resonance Structures

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 25 Resonance structures for NO 3 − are −   −   − : O : : O : : O : ║   N N N : O : : O : : O : : O : : O : : O :         Resonance Structures

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 26 Some Electron-Dot Formulas

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 27 Carbonate has three resonance structures. If the following is one, what are the other two? 2− :O: C :O: :O:     Learning Check

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 28 2−   2−   2− :O: :O: :O: │ │ C C C :O : :O: :O: :O: :O: :O:         Solution

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 29 Cyanate ion NCO − has three resonance structures. STEP 1 Determine the arrangement of atoms. N C O − STEP 2 Determine the total number of valence electrons. 1 N(5 e  + 1 C(4 e  ) + 1 O(6 e  ) + charge (1e − ) 5 e  + 4 e  + 6 e  + 1 e  = 16 e  Writing Resonance Structures

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 30 STEP 3 Attach each bonded atom to the central atom with a pair of electrons. N: C :O − STEP 4 Place the remaining electrons using single or multiple bonds to complete octets. Determine the remaining electrons. 16 valence e  - 4 bonding e  = 12 e  remaining Writing Resonance Structures (continued)

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 31 Add 12 remaining electrons as 6 lone pairs     − : N─C─O :     Form double or triple bonds to make octets     −   −   − : N=C=O : : N─C  O : : N  C─O :     Writing Resonance Structures (continued)

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 32 Write two resonance structures for nitrite, NO 2 −. Learning Check

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 33 STEP 1 Determine the arrangement of atoms. − O : N : O STEP 2 Determine the total number of valence electrons. 1 N(5 e  ) + 2 O(6 e  ) + charge (1e − ) 5 e  + 12 e  + 1 e  = 18 e  Solution

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 34 STEP 3 Attach each bonded atom to the central atom with a pair of electrons. − O : N : O STEP 4 Place the remaining electrons using single or multiple bonds to complete octets. Determine the remaining electrons. 18 valence e  - 4 bonding e  = 14 e  remaining Solution (continued)

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 35 Using a double bond completes octets and gives two resonance structures.       −       − :O=N─O: :O─N=O:     Solution (continued)