December 4
Announcements:
DO NOW Q:
Use the Lewis dot diagram to show
how hydrogen and chlorine bond
covalently.
Important Dates: (that means…write it down in your calendar)
Monday (12/8): QUIZ- Ionic and Covalent Compounds, Polarity, and 2D shapes
Review: Octet Rule
1) Most all atoms want 8 electrons in their
valence shell to be stable.
2) Ionic bonds are bonds between a (circle one)
giver / taker and a giver / taker.
3) What if you had a compound made of “takers”
of differing strengths? Hydrogen and Fluorine are
both strong “takers”. Diagram what happens when
hydrogen and fluorine react.
Polarity of Covalent Bonds
•electrons are not always shared equally in a covalent bond
•different atoms share more or less equally depending only their electronegativity
(an atom’s attraction for electrons)
• nonpolar bond: a bond in which… the electrons are
shared evenly
Examples: Oxygen Gas
(Electronegativity difference less than 0.4)
• polar bond: a bond in which… the electrons are shared
unevenly
Examples: Hydrogen Chloride and Water
(Electronegativity difference between 0.5 and 1.9)
• ionic bond: note that an ionic bond can be thought of as
a situation where electrons are shared so unequally that
an electron is essentially given/taken
Examples: Sodium Chloride (table salt)
(Electronegativity difference greater than 2.0)
Polar Molecules
If there is an imbalance of charge for the
whole molecule, the imbalance leads to a
polar molecule.
Polar Molecules
Notice that polar bonds in a molecule can give rise
to an overall charge of zero for the whole molecule.
While there are polar bonds present in the
molecule, the molecule itself is non-polar.
Solubility of Polar Molecules
• ionic compounds dissolve in water and other polar liquids
because of attraction between the dipoles and the ions
• Likewise, polar molecules easily dissolve in water because of
the attraction between the dipoles in the polar molecule and
water.
• It looks something like this…
(on whiteboard)
The general rule of solubility is…”like dissolves like”.
• Polar compounds will dissolve polar compounds
• Non-polar compounds will dissolve non-polar compounds
Determining Polarity
Polarity of the molecule depends on the polarity
of its bonds AND the shape of the molecule (in
other words, a molecule that contains polar
bonds is not necessarily polar)
Determining Polarity
1) Draw a skeleton structure. A skeleton
structure is a rough map showing the
arrangements of atoms within a molcule.
- Central atom is generally one that is least
electronegative
- or…central atom(s) is the one you have less
of
- Hydrogen and halogens are usually outside
atoms.
Example: Silicon Dioxide (SiO2)
Determining Polarity
2) Count total valence electrons
3) Connect the structure by drawing a bond
between the central atom and each outside
atom
4) Place electrons around outermost atoms
5) Place remaining electrons around the inner
most atom
You try!
1) Ammonia (NH3)
2) Water (H2O)
Using your knowledge of electronegativity, draw
dipole vectors between the different bonds
in your diagrams above.
Do you notice an overall charge in the molecule,
or do the dipoles of each bond cancel out?
If the dipoles cancel each other out, you have a
non-polar molecule.
Exceptions to Octet Rule
Exceptions to Octet Rule
or