Download Polar and Nonpolar Covalent Compounds

POLAR AND NONPOLAR COVALENT COMPOUNDS
IPC - Mr. Coburn
Introduction
The tendency of an atom to attract electrons is
called electronegativity. Atoms of elements
that have higher electronegativities "pull" the
electrons toward them with more force.
Ionic chemical bonds are formed between oppositely charged ions when valence
electrons are given away by one atom and received by another atom (or atoms). This
occurs because there is a significant difference in the electronegativity of the atoms in
the compound.
Covalent compounds exist as individual molecules that result from the sharing of
valence electrons. If the sharing is done between atoms with similar electronegativities,
the molecule is considered nonpolar. However, in a molecule that contains an atom(s)
with higher electronegativity, the compound may exhibit slight positive and negative
charges at each end of the molecule. This is known as a polar molecule.
Explore and Discuss
• Draw the Lewis Dot Diagram for a molecule of HCl.
• Consider the following illustration:
How does the illustration represent the concept of
differences in electronegativity?
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• Consider the following illustration:
If the penguin represents a hydrogen
atom and the polar bear represents a
chlorine atom, what does the ice cream
represent in the drawing? What do you
you think the picture is trying to illustrate?
Cl
H
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• Draw the Lewis Dot Diagram for a molecule of chlorine gas ( Cl2 )
• Consider the following illustration:
If both polar bears represent chlorine atoms,
atom what do you think the drawing is trying
to illustrate? Is the molecule of Cl2 polar or
nonpolar?
Cl
Cl
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Apply
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Draw the Lewis Dot Diagrams for the following compounds and identify them as
either polar or nonpolar compounds.
HBr
O2
CO2
Polar Bonds and Polar Molecules
Recall that polarity refers to an unequal sharing of electrons resulting from differences in
electronegativity. There is a distinction between polar bonds and polar molecules. A
polar covalent bond occurs when bonding electrons are more attracted to an atom
with a higher electronegativity. The polarity in the bond
is commonly represented by a arrow indicating a dipole
two charges separated by a distance). The tip of the
arrow points toward the more electronegative atom.
The polarity of a molecule is the sum of all of the bond polarities in the molecule. If
there is a greater overall polarity present in a molecule, then the molecule is polar. A
comparison of formaldehyde and carbon dioxide is shown below. Both contain polar
bonds but formaldehyde is a polar molecule while carbon dioxide is nonpolar. Since
CO2 is a linear molecule, the dipoles cancel each other.
Practice - Draw the Lewis Dot Diagrams for each of the following molecules. Show the
polarity of the bonds. Then determine if the molecules are polar or non-polar. For the
polar molecules, assign a positive and negative pole.
HF
H2CO
NaCl
CH4
For the following covalent molecules, identify them as either polar or nonpolar. If
the molecule is polar, assign a negative and positive pole.
H2O
CH4
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NH3
Cl2
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Polarity of Water
Water is a covalent compound, consisting of two hydrogen atoms and one oxygen
atom. It is covalently bonded, that is, there is an attractive force between electrons
but they are shared by the atoms.
Write the formula for water here _________________
Water is a Polar compound. This means that the electrons are not shared evenly
throughout the molecule. The oxygen attracts the shared electrons more strongly than
the hydrogen. As a result, the oxygen atom has a partial negative charge and each
hydrogen atom has a partial positive charge. The bond angle (the angle between the
hydrogen atoms) is 104o.
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Using a protractor, draw a water molecule in the box below. Label the atoms and
the bond angle. Then, label the sides of the water molecule as positive and
negative.
Polarity and Solubility
Sodium chloride dissolves easily in water due to the polar nature of water. Sodium ions
are attracted to the negative side of the water molecules and chloride ions are attracted
to the positive side of the water molecules.
In the boxes below, show the arrangement of water molecules as they would exist
around sodium and chlorine ions. Label the charge of the ions and distribution of
charges on the sides of the water molecules (as you did above).
Na
Cl
Another interesting characteristic of polar and nonpolar covalent compounds is their
solubility in certain solvents. A general rule of chemistry regarding this is "like dissolves
like". In other words, polar covalent compounds will dissolve in polar solvents and
nonpolar covalent compounds will form a solution with a nonpolar solvent.
Step 1. Pour just enough milk into the petri dish to cover the bottom.
Step 2. Place one drop of food coloring at 12:00, 3:00, 6:00 and 9:00 (as though
the petri dish were a clock).
Step 3. Observe the disposition of the food coloring and record your observations
by drawing a diagram below.
Step 4. Place one drop of soap in the center of the petri dish.
Step 5. Observe the disposition of the food coloring and record your observations
by drawing a diagram below.
Before the Addition of Soap
After the Addition of Soap
Since milk is comprised mostly of water (a polar molecule), explain the role of the soap
molecules as a means to allow the food coloring to move in the solution.
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