1 Chemical Bonding 1.Lewis Dot Structures 2.Electronegativity 3.VSEPR 4.Polarity 8 - Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2 Chemical Bonds Chemical bond –A force that holds atoms together –Ionic Bonds –Covalent Bonds 8 - Figure 8.2

3 Table 8.02

4 Ionic Bond electrostatic attraction oppositely charged ions metal and a nonmetal Electrons transferred Extremely strong bonds 8 -

5 Structures of Ionic Crystals Ionic crystal –regular geometric pattern that maximizes the attractive forces and minimizes the repulsive forces. –Hard and brittle –Can shatter if struck forcefully –Charge and size of ions determines structure 8 -

6 Ionic Bonding 8 -

7 Structures of Ionic Crystals Crystal lattice 8 -

8 Practice – Lewis Symbols Determine the valence electrons and place them Li Ca Fe Cl P 8 -

9 Covalent Bonds sharing of electrons nonmetals a neutral overall charge Electrons not transferred Electrons shared Weaker bonds than ionic bonds 8 - Figure 8.2 or another molecule picture

10 Diatomic molecules

11 Covalent Bonding –shared by two atoms –Each atom contributes one electron to the bond The orbitals overlap electron pair is between two atoms –Lewis formula atoms are shown separately valence electrons are represented by dots 8 - Figure 8.14

12 Covalent Bonding Multiple covalent bonds –more than one pair of e - shared –Double bond two pairs of electrons (4 e - total) a double bond is represented by 4 dots or 2 parallel lines –Triple bond three pairs of electrons (6 electrons total) a triple bond is represented by 6 dots or 3 parallel lines. 8 - Figure 8.17

13 Practice – Identifying Types of Bonding Between Calcium and Fluorine Ca F Between carbon and hydrogen C H 8 -

14

15 Polar vs. Nonpolar Covalent Bonds –Polar Unequal sharing of electrons different elements bonded –different electronegativities –Nonpolar Equal sharing of electrons same elements form a bond –Same electronegativities 8 -

16 Type of bond predictions Electronegativity difference nonpolar covalent equal sharing polar covalent unequal sharing > 2.0 ionic bond transfer of electrons

17 Polar vs. Nonpolar Nonpolar covalent bonds are: –Typically longer bonds –Weaker bonds Polar covalent bonds are: –Typically shorter bonds –Stronger bonds (more ionic ) 8 -

18 Practice – Polar Bonds Water 8 -

19 Polarity –polar covalent molecules –degree of transfer of electrons in a covalent bond

20 Sigma bond When two atomic orbitals combine to form a molecular orbital that is symmmetrical along the axis connecting two atomic nuclei, a sigma bond is formed.

21 Pi bond The side by side overlap of atomic p orbitals produces what are called pi molecular orbitals. When a pi molecular orbital is filled with two electrons, a pi bond results. pi bonds tend to be weaker than sigma bonds.

22 Greater difference in E- negativity between atoms –A polar covalent bond water –Increased ionic character NaCl –Decreased bond length and increased bond strength nonpolar covalent bond –e.g. H 2 (g) 8 - Electronegativity Atoms attract bonding electrons

23 Electronegativity 8 - Figure 8.5

24 Trends in Electronegativity 8 - Figure 8.6

25 Polar bonds in Non-polar molecules

26 Lewis Dot Symbols & Octet Rule –Dots represent valence electrons –Pair electrons as needed –Octet rule 8 valence electrons –Same e configuration as noble gas –8 e - exist in 4 pairs –Ions - 8 e - by losing or gaining electrons –Ex. H reacts to obtain a total of 2 electrons like He. 8 -

27 Steps for Writing Lewis Dot Structures 1.Write an atomic skeleton. atoms usually symmetrical. The central atom, the one surrounded by the other atoms, tends to be the one that is less electronegative and is present in the least quantity. Hydrogen atoms are generally on the outside of the molecule. The chemical formula may give clues 8 - Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

28 Writing Lewis Dot Structures 2.Add up all the atom’s electrons to get the total 3.Place two electrons between each pair of bonded atoms. 4.Add any remaining electrons as unshared electron pairs, consistent with the octet rule. first to complete the octet of atoms the central atom. 5.Make double or triple bonds to satisfy octet rule 8 - Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

29 Shapes of Molecules electron determine shape. electrons repel one another orbitals stay as far apart as possible. 8 - Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

30 Valence shell electron pair repulsion (VSEPR) theory –electron pairs adjust their orbitals –maximize the distance –bonded atoms and unshared pairs stay as far apart as possible Bond angle –bond angle between the central atom and the atoms bonded to it 8 - Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

31 VSEPR Parent Structures 8 - Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Table 8.5

32 VSEPR Derivative Structures 8 - Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

33 Steps for VSEPR Structures 1.Draw a Lewis formula. 2.# atoms bonded to the central atom 3.count # unshared pairs on central atom 4.# of atoms bonded + # of unshared e - 5.The total indicates the parent structure. Lone pairs + bonding pairs = shape 8 - Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

34 Natural Applications of VSEPR Theory Heme molecule –Oxygen is carried throughout the body via red blood cells containing heme molecules. –Histidine, an amino acid in the heme molecule, just fits into the space next to the oxygen molecule. 8 - Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

35 Polarity of Molecules 8 - Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Figure 8.32

36 Polarity of Molecules Diatomic molecules –Polarity lies along the plane of the bond Polyatomic molecules –A nonpolar molecule = polar bonds that cancel out –A polar molecule is one that has polar bonds that DO NOT cancel out 8 - Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.