Bond Types and Lewis Dot Structures Chemistry Section 9.5

Bond Types  Three types of chemical bonds:  Ionic – electrons are transferred  Polar Covalent – uneven sharing of electrons  Nonpolar Covalent – evenly shared electrons

Electronegativities  Definition: ability of an atom to attract electrons in a bond  Used to determine bond type by calculating the difference in electronegativities of atoms in the bond  Use Period Table of Electronegativities The electronegativity values are called Paulings (scale 0-4) Pauling

Electronegativity Table

Determining Bond Type  Ionic (I): 1.7 – 4.0, large difference indicates a transfer of electrons  Polar Covalent (PC): 0.3 – 1.7, difference is not strong enough to transfer electrons, share electrons unequally, electrons spend more time around the more electronegative atom  Nonpolar Covalent (NPC): 0 – 0.3, atoms are approximately equal in electronegativities, common in diatomic molecules and hydrocarbons

Types of Chemical Bonds - Ionic  The type of chemical bond can be predicted using the differences between the electronegativities of the elements that are bonded  An electronegativity difference between 1.7 and 4.0 is considered to be an ionic bond  Large differences between the electronegativities of two atoms indicate that an electron has been transferred from one atom to another Ionic

Determining Electronegativity Differences NaCl Ionic Bond 1.7  4.0

Types of Chemical Bonds – Polar Covalent  If the electronegativity difference is between 0.3 and 1.7, the bond is generally considered to be polar covalent  With polar covalent bonding, the electronegativity difference is not strong enough to transfer and electron. So, instead, the electrons are shared.  The sharing is not always equal because one atom will have a stronger electronegativity than the other.  When the electrons of one atom are pulled closer to the other atom, the molecule becomes polar covalent The weaker atom will become + charged The stronger atom will become - charged This is also called a dipole molecule

Identifying a Polar Covalent Bond H 2 O Ionic 1.7  4.0 Polar Covalent 0.3  1.7 Polar Covalent

Types of Chemical Bonds – Nonpolar Covalent  If the electronegativity difference is between 0 and 0.3, the bond type is nonpolar covalent  In this type of bond, both atoms are approximately equal in their electronegativities  This type of bond is most common in diatomic molecules and hydrocarbons Diatomic MoleculesHyrocarbons Br 2 N 2 ButaneC 4 H 8 O 2 Cl 2 OctaneC 8 H 16 F 2 H 2 I 2

Identifying NonPolar Covalent Bonds N Ionic1.7  4.0 PC0.3  1.7 NPC0.0  0.3 Nonpolar Covalent

Characteristics of Bond Types IonicPolar CovalentNonpolar Covalent 1.7    0.3 High Melting PointLow Melting Point SolidsSolids and LiquidsLiquids and Gases No DipolesDipolesNo Dipoles Dissolves in PCDoes Not Dissolve in NPCDoes Not Dissolve in PC

Determining Bond Type Examples  Li + Br  Li = 1.0, Br = 2.8, diff = 1.8, bond = I  C + O  C = 2.5, O = 3.5, diff = 1.0, bond = PC  C + Cl  C = 2.5, Cl = 3.0, diff = 0.5, bond = PC  K + O  K = 0.8, O = 3.5, diff = 2.7, bond = I  C + I  C = 2.5, I = 2.5, diff = 0, bond NPC

Bond Type Exercise

Bond Type Exercise Continued

“Like Dissolves Like”  Substances with like (similar) properties will dissolve in each other  Substances with unlike (dissimilar) properties will NOT dissolve in each other  Ionic and Polar compounds have charges while Nonpolar compounds have no charge

“Like Dissolves Like” Examples  NaCl (I, 2.1) dissolves in H 2 O (PC, 1.4)  Oil (NPC) will not dissolve in H 2 O

“Like Dissolves Like” Table Substance 1Substance 2Solubility?? IonicPolar CovalentSoluble IonicNonpolar CovalentNot Soluble Polar Covalent Soluble Polar CovalentNonpolar CovalentNot Soluble Nonpolar Covalent Soluble

Lewis Dot Structures  Used to predict and show structural arrangements of molecules  Shows how electrons are being shared in covalent bonds  Follows Octet Rule  Example

Lewis Dot Structures, continued  can substitute lines for pairs of shared electrons  examples

H H O Lewis Dot Structure Practice H2H2 H2OH2O  H = 1 valence e-  O = 6 valence e- HH—H H—O—H H

Cl C More practice…  CCl 4  C has 4 valence e-  Cl has 7 valence e- Cl Cl—C—Cl Cl

Steps for Lewis Dot Structures 1. Determine the number of valence electrons for each element 2. Determine the central atom (atom with lowest electronegativity value) 3. Write the central atom and valence electron dots 4. Fill in the remaining elements with their valence electron dots

Lewis Dot Structure Practice  Draw Lewis Dot Structures for the following compounds: CF 4 CH 4 Cl 2 NF 3 H 2 PCl 3