I. Covalent Bonds A. These bonds are formed from twoatoms _________ electrons, so each atom will have a filled outer energy level. sharing 1 dash represents 2 electrons A bond is drawn as a dash: This is called a Structural Formula B. Three types of bonds can be formed: 1 pair of electrons are shared between 2 atoms, 2e- total Single - 2 pairs of electrons are shared between 2 atoms, 4e- total Double - 3 pairs of electrons are shared between 2 atoms, 6e- total Triple -
II. Bond Formation A. Covalent bonds are formed from two or more ______________ ONLY, which are found in groups: nonmetals 4A-7A • The sharing of e- will allow each atom to achieve a stable noble gas e- configuration. • Each atom will have 8 valence electrons or a full octet creating filled orbitals. Exception: Cl Cl H H Stable configuration Circle the shared electrons
III. Review Ionic Compounds vs. Covalent Compounds Ionic Bonds Covalent Bonds Anion & cation 2 or more nonmetals Transfer e-: Arrow is used Share e-: Circle the e- shared between the2 atoms Chemical Formula = Formula Unit Chemical Formula = Molecular formula A line is notused to represent a bond, why? A line is used to represent a bond, why? Share e- Don’t share e-
Covalent Bonds two atoms share e- One pair of electrons Two pairs of electrons Three pairs of electrons called called called Single bond Double bond Triple bond Drawing covalent molecules takes practice & patience! Practice makes perfect!
Bond Polarity Bond Polarity pairs of electrons may not be shared equally. greater electronegativity greater attraction/bonding e- to itself. Bond type found by difference in electronegativity subtract the two numbers. 3 types of bonds.
CovalentPolar Microwavid. Covalent Nonpolar Ionic 0 - 0.49 0.50 – 1.9 2.0+ sharedequally not sharedat all! sharedunequally
CH4 Methane C H 2.5 2.1 = 0.4 The atom that is more electronegative (stronger attraction of e-) acquires a semi-negativecharge & the less electronegative acquires a semi-positive charge. A delta symbol is used to showthe attraction. C Br = 0.3 2.8 2.5
HCl Hydrochloric A. Cl H = 0.9 3.0 2.1 Arrow points to the more electronegative element. The bonding electrons are displaced more towards the atom with the higher electronegativity. C F 4.0 = 1.5 2.5
The more electronegative element, Cl, attracts the bonding electrons more.
Example - Ionic Na+ Cl- = NaCl 0.9 3.0 = 2.1 The electrons are not shared between the two atoms but they are: Transferred Therefore:arrows & partial charges are not drawn because the e- are NOTshared. = K2O K+ O2- 0.8 3.5 = 2.7
More Examples: NH4 ammonia N H = 0.9 3.0 2.1 F F 4.0 4.0 = 0.0 Why is an electronegativity arrow not drawn over F2? It is a non-polar bond!
Reading Quiz 16-2 1. When atoms in a molecule equally share electrons, the bond formed is ____________. 2. Unequally shared electrons are found in __________ bonds. 3. The bond type can be found by subtracting the two atom’s _____________ numbers. 4. In a polar molecule, one end of the molecule is slightly __________ and the other end is slightly __________. 5. A molecule that has two poles is called a _____.
DRAWING COVALENT LEWIS DOT STRUCTURES RULE 1 “ C N O F” RULE 2 4 3 2 1 # BONDS RULE 3 ADD enough valenc e- RULE 4 ADD/SUBT e’s for +/- pos ions LETS TRY H2O NH4+ CO32- FCN F2 H2 N2 CN-
O C O H H Draw the structural formula for HCOOH, with electronegativity numbers and arrows.
CH2O NOH H2S CH3Cl CH4 H2O2 H2SO4 CF4 CBr2H2 CH3NH2 HCl CO SO3 Exceptions Odd # valence NO2
■Acetic acid C2H3O2 ■Acetone ■Acetylene C2H2 ■Carbon tetrachloride CCl4 ■Hexane C6H14 ■Carbonic acid H2CO3 ■Dichloro-difluoro-methane C2Cl2F2 ■1,2-Dichloroethane C2H4Cl2 ■Dichloro-difluoro-methane CF2Cl2 ■Dimethyl sulfide CH3SCH3 ■Ethane C2H6 ■Ethanol C2H5 ■Ethene C2H4 ■butane C4H10 ■propanol C3H7OH ■Methanol CH3OH ■Pentane C5H12 ■Propane C3H8 ■Propionic acid C3H5O2H ■Propyne C3H4 OH
Exceptions to the Rules Odd # valence NO2 Incomplete octets MgH2 LiH AlH3 BF3 Expanded Octets SF6 PCl5 XeF4 SeF4 Resonance O3
Molecular Polarity Molecular Polarity Definition: Dipole - A molecule that has 2 poles, one end is partially (+), the other end is partially (-). Must know:1 - bond polarity & 2 - molecular shape (VSEPR)to predict molecule polarity!
Molecular Polarity Definition - Polar Molecule 1. Must have at least 1 polar bond.This is required! 2. Most molecules with lone pairs on the central atom are polar! ex: bent &pyramidal 3. Tetrahedral shape must be unsymmetrical 105o ex: CH3Cl Different atoms bonded to the central atom.
Molecular Polarity Definition - Nonpolar Molecule 1. May have polar bonds.(not required) 2. Molecules with nolone pairs on the central atom are usually nonpolar. ex: trigonal planar & linear 3. Tetrahedral shape must be symmetrical! ex: CH4, CF4 (all atoms bonded to the central atom are the same)
Example 1 Electronegativity difference O-H:3.5 - 2.1 = 1.4 Bond polar or nonpolar? O 3.5 H H 2.1 2.1 Draw the structural formula for H2O Polar or Nonpolar Molecule Why??
Example 2 2.5 3.5 3.5 C O O Electronegativity difference O-C:3.5-2.5 = 1.0 Bond polar or nonpolar? Draw the structural formula for CO2 Polar or Nonpolar Molecule Why??
Molecule of Butane Carbon Hydrogen
Example 3 Electronegativity difference Cl-C:3.0-2.5 = 0.5 3.0 Cl Bond polar or nonpolar? 2.5 Bond polar or nonpolar? C H H 2.1 2.1 H Electronegativity difference C-H:2.5-2.1 = 0.4 2.1 Draw the structural formula for CH3Cl Polar or Nonpolar Molecule Why??
Example 4 2.1 H Electronegativity difference C-H: 2.5 - 2.1 = 0.4 2.5 C Bond polar or nonpolar? H H H Why?? Draw the structural formula for CH4 Polar or Nonpolar Molecule
Example 5 Electronegativity difference P-H:2.1-2.1 = 0 2.1 Bond polar or nonpolar? P H H H 2.1 Draw the structural formula for PH3 Polar or Nonpolar Molecule Why??