Electronegativity Difference and Bond Character



Electronegativity Difference and Bond Character

Covalent bond - a shared pair of electrons between two atoms

Electronegativity - the ability of an atom to attract electrons in a covalent bond.

Electronegativity Difference, ΔE = E1-E2,

For example, each H—–O bond in H2O has: ΔE = EO - EH

ΔE = 3.44 - 2.10

ΔE = 1.44

As the electronegativity difference grows from 0.00 to >3.0, the sharing of electrons becomes more skewed. First one atom becomes partially negative while the other becomes partially positive and the bond is polarized, polar covalent bond. Then as the sharing becomes more and more unequal, the electrons reside only on one atom. The atoms are now ionized (+ or -), and the bond is called ionic. This is shown in Table 1.

Table 1

|Electronegativity Difference, ΔE |0.00 |0.65 |

| ΔE = 0.00 |nonpolar |pure covalent |

| 0.00 < ΔE < 0.65 |nonpolar |covalent |

| 0.65 < ΔE < 1.67 |polar |covalent |

| 1.67 < ΔE | |ionic |

More on Dipoles

• An electric dipole consists of two opposite charges that are the same magnitude and separated in space.

• Unequal sharing of electrons (ΔE > 0) results in one end of the bond being negative and one end being positive. This is a dipole (2 poles, one negative, one positive)

• The atom with the greater electronegativity becomes partially negative, δ-,

• The atom with the smaller electronegativity becomes partially positive, δ+.

• Drawing an arrow from δ+ to δ- shows the electric field between the charges.

Practice Problem: Hydrogen fluoride, HF

o Draw the Lewis Structure

o Determine the polarity and bond type for each bond.

o Draw the dipole for each bond.

HF, would be written as H—– F

Since ΔE = 1.10, the bond is polar covalent. {ΔE = 3.98 - 2.10 = 1.10}

F has the greater electronegative so it is partially negative, δ-, and H with the smaller electronegativity is partially positive, δ+. So on your structure you should draw the following dipole

Final Answer: H —– F

δ+ → δ- polar covalent

Name: Chemistry

Period: Date: Dr. Mandes, Ph.D.

Directions For each formula, • draw the Lewis Structure and geometry (2 pts. each)

• determine the bond type (3 pts. each)

• draw the dipole. (3 pts. each)

1. CBr4

2. CH3SH

3. PH3

4. K2O

5. HCl

6. CH2O

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