Bonding Class #3 OB: introduction to covalent bonding (2 or more nonmetals that share valence electrons – they do not transfer them like ionic compounds do).

With ionic bonding, there is a TRANSFER OF ELECTRONS FROM METAL → NONMETAL They still follow the octet rule (mostly). Ionic bonds require a metal to be first in the formula. Ionic bonds make formula units (FU’s). In Covalent Bonding, there is A SHARING OF THE VALENCE ELECTRONS, AND THE ATOMS WILL FOLLOW THE OCTET RULE. NO METALS in any covalent bonds. Covalent bonds form molecules.

Molecules form with covalent bonds (sharing electrons) following the octet rule almost every time. Let’s draw H 2 F 2

Molecules form with covalent bonds (sharing electrons) following the octet rule almost every time. Let’s draw H 2 H H F 2 Br Br

In covalent bonds, all atoms get to share enough electrons so that they get full outer valence orbitals at least some of the time. These bonds previous are all SINGLE BONDS because they only share a single pair of electrons (one electron from each atom). They are also NONPOLAR bonds because there is NO DIFFERENCE IN electronegativity value between the atoms. They’re called SINGLE NONPOLAR COVALENT bonds Draw the Lewis Dot Diagrams for HCl and then, for water.

HCl H 2 0

Let’s see if we can draw the Lewis Dot Diagrams for HCl and then, water. H Cl The hydrogen atom in black has one valence electron. The chlorine, in red, has 7 valence electrons. Together the hydrogen gets to borrow one electron from chlorine to fill its tiny orbital, and chlorine gets to borrow one electron from hydrogen to fill its larger orbital (octet rule). H O H Here, the hydrogen are black again, and need to borrow one electron from oxygen each, to fill their tiny orbitals. Oxygen borrows one electron from each of the hydrogen atoms, to fill up its larger orbital (octet rule). Water is bent, don’t forget! We’ll learn why soon enough! The red/black colors are not important, “just for seeing” it better as we learn at the beginning.

H Cl H O H The bond between H and Cl is between atoms with 2 different electronegativity values. What are their EN Values? Is this a polar bond, or a nonpolar bond? How about here? What are the EN Values for H and for O? Polar or nonpolar bonds?

H Cl H O H NAME THIS BOND _____________________________ There are 2 identical bonds here (both H-O). Name THESE BONDS There are 2… ___________________________

H Cl H O H Another way to draw this, with a lot less dots, is called a structural diagram. With a structural diagram, we only show the bonds, with short lines indicating shared electrons. A single dash represents a single covalent bond. Draw both of these molecules now.

H Cl H ―Cl H O H Structural Diagrams H―O H This is a bit turned, but molecules move in 3 dimensions. It’s fine this way, or pointing in any other way.

Draw the Lewis Dot Diagram for AMMONIA (NH 3 ), then the structural diagram. NAME THESE 3 BONDS TOO. Think first: N Nitrogen has 5 valence electrons, and they will be paired up in a Lewis dot diagram (and real life) because this is more stable. To bond, one pair will have to open up to connect with 3 hydrogen atoms. N Bring in the 3 hydrogen atoms… H H H

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N H H H H ―N―H H Ammonia as Lewis Dots, and as a structural diagram. Checking the electronegativity values, we see that H has a 2.2 while N has a 3.0 These bonds are all single polar covalent.

Draw Lewis Dot Diagram, and Structural Diagram for Methane, CH 4 Determine exactly what types of bonds are present in this molecule.

Draw Lewis Dot Diagram, and Structural Diagram for Methane, CH 4 Determine exactly what types of bonds are present in this molecule. C H HH H H ―C―H H H Electronegativity values of 2.2 for H, and 2.6 for N, so there are 4 single polar covalent bonds in a molecule of CH 4

The greater the difference in electronegativity values between two atoms, the greater the polarity of the bond. This works like little +/- magnets. Some magnets are stronger (greater EN difference) and some magnets are weaker (lesser EN difference). Fill in this chart, and then RANK from the greatest polarity of the bond (1), to the weakest (5). Polarity rank Molecule/ name EN #1 EN #2 EN diff Structural diagrams H 2 hydrogen 2.2 0H ―H PCl 3 OF 2 HBr HI

Polarity rank Molecule/ name EN #1 EN #2 EN diff Structural diagrams 5 H 2 hydrogen 2.2 zero this is a nonpolar bond H ―H 1 PCl 3 phosphorus trichloride Cl―P―Cl 3 OF 2 oxygen difluoride HBr hydrogen bromide H ―Br 4 HI hydrogen iodide H ―I FF O Cl

How do 2 oxygen atoms stay together in O 2 ? Let’s draw two atoms Lewis Dot to start our thinking. O O How many electrons does EACH atom of oxygen need to complete the octet? Can they do this for each other? Hint: move the bottom pairs of electrons to the open sides.

O O Squeeze them together now (this requires you redraw) O In order to both get an octet, the oxygen atoms must share 2 pairs of electrons with each other. This gives the oxygen molecule a DOUBLE COVALENT BOND. Since each atom of oxygen has the same electronegativity value, it’s proper to call this a: Double Non-Polar Covalent bond O