Chemistry

• Chemistry
• 10th Grade

Electronegativity Topic

Objectives

• Understand valence electrons
• Understand sharing electrons (bonding)
• Understand partial charges
• Understand electronegativity

An elemental carbon's parts are shown above. The number of protons and electrons are the same, which is consistent throughout the elements. 

Nucleus

Electron

Proton

Neutron

Carbon, 

which is the 6th element on the periodic table has 6 protons and 6 electrons. Likewise, Neon (Ne), the 10th element on the periodic table has 10 protons and 10 electrons. This is how all of the elements on the periodic table are organized. 

The electrons on the outer shell are called valence electrons. Carbon is satisfied when it has 8 valence electrons which is true for all gases except for hydrogen (H) and helium (He).

Hydrogen (H) and helium (He) are satisfied with only 2 electrons on the inner valence shell. 

The outer shell is 

satisfied with 8 valence

 electrons after the first 

shell is completed with 

2 valence electrons . 

After the second valence 

shell is filled with 8 

valence electrons,

this would start 

another shell with 

another 8 possible valence 

electrons.

How do molecules gain electrons to fill their valence shell?

In order for molecules to fill their valence shell, they can share electrons. 

Oxygen (O) the 8th element and Hydrogen (H) for example, share electrons to form water, 

H2O. 

1 hydrogen shares a valence electron with 1 of oxygen's valence electrons. Both of the hydrogens sharing 1 electron each creates 2 bonds. 

Filling the Valence Shell

Oxygen, being the 8th molecule, 

has 8 electrons with a full inner valence shell of 2 electrons, and 6 electrons on the outer valence shell. Sharing electrons with Hydrogen completes it's need to have a balanced charge between negatively charged electrons and positively charged protons. 

This image of a water molecule shows the partial charges on the molecule. The partial charges are the symbols with the (+) and (-) beside them. 

Electronegativity

The partial charges on the molecule indicate the electronegativity of the element on the molecule. Oxygen has the greater negative charge because it is more electronegative.

Electronegativity

Oxygen is more electronegative than hydrogen because of its position on the periodic table. The arrows indicate increasing electronegativity. The exceptions to this are the molecules all the way on the right which are called the noble gases. They already have 8 valence electrons. 

Therefore, they  are not very electronegative because their valence shell is already satisfied with 8 valence electrons. 

The following slide contains a link to this simulator. Select "3 atoms" and increase the electronegativity of (B) to show how an oxygen on a water molecule behaves with a partial negative charge. Check the Partial Charges box and turn on the Electric Field to understand 

how this molecule behaves with respect to other charged compounds. 

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