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Polar Covalent Bonds. Trends in the Periodic Table and Bonding. -. -. -. -. +. +. +. +. Covalent Bonding. A covalent bond is a shared pair of electrons electrostatically attracted to the positive nuclei of two atoms. Both nuclei try to pull the electrons towards themselves .

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Polar Covalent Bonds

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Polar covalent bonds l.jpg

Polar Covalent Bonds

Trends in the Periodic Table and Bonding


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+

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Covalent Bonding

A covalent bond is a shared pair of electrons electrostatically attracted to the positive nuclei of two atoms.

Both nuclei try to pull the electrons towards themselves

The atoms achieve a stable outer electron arrangement (a noble gas arrangement) by sharing electrons.

This is like a tug-of-war where both sides are pulling on the same object.

It creates a strong bond between the two atoms.


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Covalent Bonding

Picture a tug-of-war:

If both teams pull with the same force the mid-point of the rope will not move.


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H

H

e

e

Pure Covalent Bond

This even sharing of the rope can be compared to a pure covalent bond, where the bonding pair of electrons are held at the mid-point between the nuclei of the bonding atoms.


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CovalentBonding

What if it was an uneven tug-of-war?

The team on the right are far stronger, so will pull the rope harder and the mid-point of the rope will move to the right.


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Polar Covalent Bond

A polar covalent bond is a bond formed when the shared pair of electrons in a covalent bond are not shared equally.

This is due to different elements having different electronegativities.


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δ-

δ+

H

e

e

I

Polar Covalent Bond

e.g. Hydrogen Iodide

If hydrogen iodide contained a pure covalent bond, the electrons would be shared equally as shown above.

This makes iodine slightly negative and hydrogen slightly positive. This is known as a dipole.

However, iodine has a higher electronegativity and pulls the bonding electrons towards itself

(winning the tug-of-war)


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δ-

δ+

C

Cl

Electronegativities

Polar Covalent Bond

In general, the electrons in a covalent bond are not equally shared.

e.g.

3.0

2.5

δ- indicates where the bonding electrons are most likely to be found.


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C Cl

2.5 3.0

P H

2.2 2.2

O H

C Cl

O H

3.5 2.1

P H

δ-

δ+

δ-

δ+

Polar Covalent Bond

Consider the polarities of the following bonds:

Difference

Electronegativities

Bond

0.5

0

1.4

Increasing Polarity

Complete a similar table for C-N, C-O and P-F bonds.


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