Chemical Bonding revised

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Electronegativity

For main group elements, electronegativity tends to increase with the group number (left to right on the periodic table).

Notice the noble gases do not have electronegativities, why is that?

Electronegativities also increase as you move vertically up a group number.

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Atom Size

For any period in the periodic table, as you move right the size of the atom decreases

Why does this trend exist?

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Atom size

As the number of protons increases, the force attracting the electrons increases

The electrons are pulled closer to the nucleus of the atom

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Polarity

The difference of electronegativity between two bonding atoms can be measured by subtracting the smaller number from the larger number.

The difference in the two electronegativities determines the nature of the bond

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Polarity

Bonds that are sharing electrons UNEQUALLY between two atoms are called POLAR COVALENT BONDS

If the atoms are identical (equal electronegativity), the bond will not be polar. This is called NON-POLAR COVALENT BONDS

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Polar covalent bonds have a positive “pole” and a negative “pole” so they are also referred to as “bond dipoles”

Polar covalent bonds have an electronegativity difference between 0 and 1.7

Ionic bonds have an electronegativity difference between 1.7 and 3.3

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Polar Molecules

Are molecules that contain polar bonds necessarily polar?

Examples of H2O and CO2

To determine if a molecule is polar we need to look at the overall direction of polarity

Draw in polarity arrows on your molecule and determine if the molecules are polar or not

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Ionic Bonds

Ionic bonds form from the electrostatic attraction between oppositely charged ions

Atoms become ionic by losing or gaining electrons from the atom it is bonding with

Remember that an atom will lose its electrons to fill its outer level if its valence level is less than half full, as it is with metals

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