Bonding Class #5

OB: more practice with Lewis Dot diagrams, Structural Diagrams, and we get to meet the

weird hybrid bonds of ozone, carbon monoxide, PCl5, and NO2

Lots of paper, fresh minds, periodic tables at the ready!

First we draw 2 diagrams, (structural or dots), and determine the types of bonds present.

calcium oxide + butane C4H10.

calcium oxide butane C4H10.

[Ca]+2[O]-2This is an IONIC bond, due to the transfer of electrons from calcium to oxygen.

H-C-C-C-C-H

H H H H

H H H H

This has single non polar covalent bonds at the C-C locations, and single polar covalent bonds at the C-H locations

Make sure you don’t forget that metals will only make IONIC bonds!

Now, let’s look over the model of NaCl crystal (and the diagram here).

Each Na+1 cation is surrounded by 6 Cl-1 ions.

The reverse is also true,

Each Cl-1 ion is surrounded by 6 Na+1 cations

We can say that theCOORDINATION

NUMBER for chloride is 6,

and that the COORDINATION

NUMBER for the sodium cations is also 6.

Big deal, right?Well, the coordination number, at the ion level, will give rise to specific shapes to the salt crystals when they grow up to be big enough to see with your eyes.

Uric Acid crystals look like this:

Cute little swords, really.

They cause gout, which is what can happen to your teacher from time to time.

The last time my sister in law Andrea made Portobello mushroom appetizers for Christmas (a few months ago), I woke up at 3 AM unable to sleep, and I could not drive home the next day, because of those crystals (all making home in my big toe!).

Let’s work on carbon monoxide now, how does it bond together?

CO2 is so important, straight line, two double polar covalent bonds, but what about it’s little cousin, CO?

C O

This will be an exceptional bond, with a cool name too. Here goes…

C OCan we share 4 + 6 to get two octets? This is tricky!

C OLooks like a polar double

bond is in order, but

carbon has no octet yet.

86

C O

So, oxygen will “lend” 2 of it’s unshared electrons to the bonding “mix”, and it keeps an

octet, and although they are not bonded in the

same way, carbon “gets” an octet too.

C OIt will form a double polar covalent bond and also form what’s called aCOORDINATE COVALENT BOND.

The oxygen electrons coordinate this situation so that carbon “gets” an octet in a sort-of cheating way. Weird, but it happens!

C=O~My shorthand for this type of bond

Phosphorus pentachloride is up next, a real but weirdo molecule…

It’s used as part of fertilizer preparation, and other chemical reactions. Draw the dot diagram.

Phosphorus Pentachloride PCl5

PCl

Cl

Cl

ClCl

This compound breaks the octet rule, how many electrons does phosphorus end up with? How is this possible? Isn’t it a rule???

The compound called 2-pentene has five carbons in a chain, similar to octane (8) that we drew yesterday. The #2 means that the one double bond fits between the 2nd and 3rd carbon in the chain. Only hydrogen atoms are bonded to this set of five carbon atoms. Can you draw the dots here, then the structural diagram?

(I dare you to try, no talking 2 minutes! My kids can do anything!)

The compound called 2-pentene has five carbons in a chain, similar to octane (8) that we drew yesterday. The #2 means that the one double bond fits between the 2nd and 3rd carbon in the chain. Only hydrogen atoms are bonded to this set of five carbon atoms. Can you draw the dots, and the structural diagram? (I dare you to try, no talking 2 minutes! My kids can do anything!)

H―C ―C C ―C―C―H

H

H

H H

HH

H H

C5H1

0

John Adams High School, in Ozone Park, New York

City at left. I graduated in 1978 on that sidewalk out in front of the school. We

had 2 graduations that day, 975 kids were too

many for one ceremony!

Both my sister and my brother worked here, and they had the best crumb buns in the world. And the cookies were fab too.

Those stairs go up to the A Train to Manhattan. It’s only the subway in Manhattan, most of Queens the subway runs on the el.

Ozone and Oxygen, both pure oxygen, but one you breathe to live, one you breathe to die. (sorry).

O3 vs. O2

You already know that oxygen has a double, nonpolar, covalent bond. No need to review (right?).

Ozone is an ALLOTROPE of oxygen. Allotropes are pure forms of an element but due to different bonding, they have different properties. Other allotropes are carbon in the graphite mode and carbon in the diamond mode!

Try to bond 3 oxygen atoms…

O

O O

O

OOWith ozone (and other molecules, like NO2, the electrons can’t add up to full octets all around. In this case, the oxygen atoms become “most” stable by making a double bond and a single bond, which RESONATES, back and forth. It’s a resonating bond.

In reality, this switching back and forth is constant, and becomes in fact, two “one and a half bonds” all the time. Scientists know this because they can measure the bond lengths. Single bonds are longer than double bonds. These “resonating” bonds are 1½ sized all of the time.

Getting the ozone bonding, the RESONATING bonding correct on the regents is a very personal thing for me. If you have any kindness in your heart for me, please remember this bond and how it is a “hybrid” bond (abnormal, like me!)