Ch 8 Covalent Bonding.notebook
November 28, 2012
Chapter 8 Covalent Bonding
Ionic bond— involves transfer of electrons to get 8 electrons in outer energy level.
Molecular formulas Smallest particle called a formula unit
Ammonia NH3
ex: NaCl, CaCl2
Made of a metal and a nonmetal
Covalent Bond—involves sharing of electrons to get 8 electrons in outer energy level.
Smallest particle called a molecule
ex: CCl4, CO2
Water H2O
Made of 2 nonmetals
Molecular compounds have lower melting points and boiling points than ionic compounds ex sugar
diatomic molecule –made of 2 atoms
7 diatomic elements: H O F N Br I Cl
H2 O2 F2 N2 Br2 I2 Cl2
Nov 9­10:07 AM
Nov 9­10:53 AM
Single bonds:
Hydrogen molecule:
Single covalent bond: share 1 pair of electrons
Double covalent bond: share 2 pairs of electrons
Triple Covalent bond: share 3 pair of electrons
Fluorine molecule
Water molecule
Methane molecule
Nov 9­10:53 AM
Nov 9­10:54 AM
1
Ch 8 Covalent Bonding.notebook
November 28, 2012
Double Bond:
Carbon dioxide
Oxygen
p 222 table of Diatomic elements
p. 224 table of
Common
Molecular compounds.
Triple bond
Nitrogen
Nov 9­10:54 AM
Nov 9­10:55 AM
bond dissociation energy:
Coordinate covalent bond: one atom contributes both electrons to a bond energy needed to break a bond between 2 covalently bonded atoms.
Carbon monoxide
This energy is very high. Tough to break covalent bonds.
Resonance: Ozone p 227
A structure when it is possible to draw 2 structures for a molecule
Exceptions to the octet rule p228
Nitrogen dioxide
Sulfur hexafluoride
Nov 9­10:55 AM
Nov 26­10:04 AM
2
Ch 8 Covalent Bonding.notebook
November 28, 2012
Bond Polarity: how equally electrons are shared in a covalent bond
VSEPR Theory p 233 Non polar covalent: shared equally. Diatomic elements
predicts shapes of molecules based on number of atoms,bonds, bond types and unshared pairs of electrons.
Polar covalent bond—electrons are shared unequally.
The more electronegative element attracts the electrons more closely. (p 177 electronegativity values)
Ex: water
HCl
Nov 26­10:10 AM
Nov 9­10:56 AM
Polar molecules: one end slightly negative, one end slightly positive.
Hydrogen bonds­hydrogen is covalently bonded to a very electronegative atom (O, F, N). Hydrogen bonding is important to life on earth.
Attractions between molecules:
Intermolecular attractions are weaker than bonds.
Van der Waals forces—weakest attraction between molecules (2 types)
1.
Dispersion forces­­­caused by motion of electrons
2.
Dipole interactions­­­­caused by polar molecules attracting each other.
Nov 9­10:56 AM
Nov 9­10:56 AM
3
Ch 8 Covalent Bonding.notebook
November 28, 2012
Network solids­­­3 dimensional structure of covalent bonds. Ex: diamond very high melting point
p 244 table comparing ionic and covalent compounds
Nov 9­10:57 AM
4