Electronegativity, Polarity & Delta Notation

Question 1

What is electronegativity?

Answer 1

The ability of an atom to attract electrons

Question 2

What is the octet rule? And how does it relate to electronegativity?

Answer 2

The octet rule is that atoms are trying to achieve a state where they have 8 valence electrons. And an element’s electronegativity is determined by how close an atom is to filling its octet.

Question 3

What is an example of electron affinity?

Answer 3

Lets use Fluorine and Sodium as an example. Atoms that are close to having 8 valence electrons have a high electronegativity. Fluorine has 7 valence electrons so even though it needs 1 more to be a full octet, it has a high electronegativity.

Atoms that are not close to having 8 valence electrons have a low electronegativity. Sodium has just 1 valence electron and needs 7 more for a full octet, so it has a low electronegativity.

Question 4

What is the symbol of electronegativity? And what does it mean?

Answer 4

The symbole is “EN.” It means a number with no unit.

For example, Sodium has a low EN value of 0.9 so there’s low attraction. Fluorine a high EN value of 4.0, so there’s high attraction.

See Periodic Table in Files

Question 5

What is the correlation between losing and gaining electrons and electronegativity?

Answer 5

Elements that lose electrons (metals) tend to have low electronegativity. Elements that gain electrons (non-metals) tend to have high electronegativity.

Question 6

Why are noble gases exceptions to electronegativity?

Answer 6

Nobel gases have full octets and don’t need anymore electrons. They have 0 electronegativity.

Question 7

What is the tread of electronegativity using a periodic table?

Answer 7

Electronegativity increases as you go left to right amd bottom to top on the period table.

Question 8

How do you find an electronegativity value of an element?

Answer 8

On the periodic table, each element is assigned an electronegativity value that quantifies its electronegativity.

Question 9

How does a molecule become polar?

Answer 9

In a covalent bond when electrons are not shared equally it becomes polar.

Question 10

Why does the unequal sharing of electrons happen?

Answer 10

Elements have different electronegativity so most of the time electrons are not shared equally.

The more electronegative atom pulls on the shared electrons just a little bit more than the other atom.

Question 11

What is the function of finding the difference in electronegativity values (EN)?

Answer 11

To determine the type of bond present and if a molecule is polar

Question 12

What are the 3 EN types of bonds?

Answer 12

1. EN = 0 is a non-polar covalent bond
2. EN = 0.1-2.0 is a polar covalent bond
3. EN = 2.1 or over is an ionic bond

Question 13

Describe non-polar covalent bonds

Answer 13

1. No polarity in the molecule
2. Perfectly equal sharing of electrons

Example: Hydrogen
EN for H = 2.1
2.1-2.1 = 0

Question 14

Describe polar covalent bonds

Answer 14

1. Polarity in the molecule
2. Unequal sharing of electrons

Example: EN = Fluorine and Hydrogen
= 4.0-2.1= 1.9

Question 15

Describe ionic bonds in terms of electronegativity values

Answer 15

1. A lot of polarity so the bond is not covalent anymore

Question 16

What is the function of delta notation?

Answer 16

To show the direction of polarity in a chemical bond.

Question 17

What types of directions will delta notation show?

Answer 17

It will show which pole of the bond is slightly negative and which pole is slightly positive as a result of electronegativity.

Question 18

What are the 3 symbols and signs of delta notation?

Answer 18

1. δ+
   A delta + symbol showing the slightly positive “pole” of the molecule.
2. δ−
   A delta − symbol showing the slightly negative “pole” of the molecule.
3. A right arrow (→) or left arrow (←) pointing towards the negative pole of the molecule.

Question 19

Draw a delta notation of hydrogen and chlorine and explain what it means

Answer 19

Step 1: Determine the electronegativity values. H = 2.1
CI = 3.0

Step 2: Subtrate the values and classify the bond. If the bond is polar covalent, proceed to step 3. If the bond is anything else, stop.
3.0-2.1 = 0.9. This is a polar covalent bond.

Step 3: Draw an arrow that points to where the electrons are being pulled more: H → CI
- The arrow shows that the positive end is on hydrogen and that the electrons are pulled towards chlorine.

Step 4: Use delta notation to show the poles of the molecule:
δ+ δ−
H → CI

Tie it all together: Chlorine (CI) has a partial negative charge because it has the greater electronegativity (δ−) and Hydrogen (H) has a partial positive charge (δ+). These are the poles of the molecule.