Objectives:
Covalent Bonds
use electronegativity to determine the bond character, explain and predict the formation of covalent bonds, and identify
properties of covalent bonds
Covalent Bonds are formed when electrons are shared
Polar Covalent Bonds-unequally shared
 The EN difference is: between .3 and 1.7
(Remember—EN is the ability of an atom to pull an electron toward itself in a bond.)
Example: HCl
 One element has higher EN
 The electron spends more of the
and the other element has
time with the higher EN
lower EN
element thus distorting its cloud
NON-Polar Covalent Bonds-equally shared
 The EN difference is: less than .3
(Remember—EN is the ability of an atom to pull an electron toward itself in a bond.)
Example: H2
 Both elements have similar EN values
How can bonding be used to predict properties?
 The electron is equally shared
by both atoms
T. O’Toole
Covalent Compound Properties
Covalent properties tend to be opposite of ionic. They will vary though depending on
whether the molecule has a distorted electron cloud with charged poles or if it is
symmetrical.
 Covalent compounds are soft solids, liquids, or even gases at room
temperature
Soft solids and liquids are most likely PC bonded since the dipole molecules will attract
each other to some extent.
Liquids with low boiling points and gases likely exist as individual mo lecules like H2 and are
therefore most likely NPC bonded.
 Covalent compounds have much lower melting and boiling points than
ionic compounds
Generally speaking, PC bonded compounds will have MP and BP higher than NPC bonded
compounds because their molecules are dipoles and therefore are somewhat attracted to
neighboring molecules making them harder to separate.
 Covalent compounds generally do not conduct electricity
Neither polar covalent nor non polar covalent substances conduct electricity in water.
Electricity requires ions to carry the charge and there are no ions in covalent bonds.
How can bonding be used to predict properties?
T. O’Toole
 Covalent compounds are not very soluble in water
Water is a polar covalent substance and will therefore dissolve polar covalent bonded
substances.
Non polar bonded substances will be minimally soluble in water.
Minute Paper
Determine the EN difference for the compound calcium sulfide
Draw the electron dot diagram for this molecule. Does this molecule have a permanent dipole?
How do I get from where I am to where I’m going?
The 10 Minute Makeover
Customize your learning by choosing from the following options each night
 Complete the appropriate section on the Portfolio Page
 Complete the SYS Assignment: “Ionic and Covalent Bonds”
 Complete the SYS Assignment related book work
 Review the PPT file on the website
 Read pages 437-440 in the book
 Practice using: http://www.quia.com/jg/1276939.html
 Review the skills from today’s Train Your Brain
How can bonding be used to predict properties?
T. O’Toole