Electronegativity and bonding

Electronegativity values can be used to predict the polarity of bonds. Explain the term electronegativity.

Electronegativity is the ability of a particular atom, which is covalently bonded to another atom, to attract the bond pair of electrons towards itself.

On the Pauling scale the electronegativity's of nitrogen and oxygen are respectively 3.0 and 3.5. Why is oxygen more electronegative than nitrogen?

Oxygen has 8 protons in the nucleus whereas nitrogen only has 7. A bonding pair will experience more attraction from the oxygen's nucleus than from nitrogen's, and so the electronegativity of oxygen is greater.

The electronegativity values for some atoms are given below: 

H = 2.1, C = 2.5, F = 4.0, Cl = 3.0, I = 2.5

Use these values to predict the polarity of each of the following bonds by copying the bonded atoms shown below and adding δ+ or δ– above each atom.

i. H-I

ii. F-I

iii. C-Cl

Electrons in the bond won't be shared equally.

i. Hydrogen electronegativity value is 2.1 but Iodine is 2.5, so electrons in the covalent bond will be more attracted to iodine. The electron cloud will be more distorted towards iodine => The iodine end is relatively negative and the hydrogen is relatively positive, electron deficient. δ+H -- δ-I

ii. Fluorine electronegativity value is 4.0 but Iodine is 2.5, so electrons in the covalent bond will be more attracted to fluorine. The electron cloud will be more distorted towards fluorine => The fluorine end is relatively negative and the iodine is relatively positive, electron deficient. δ+I -- δ-F

ii. Carbon electronegativity value is 2.5 but chlorine is 3.0, so electrons in the covalent bond will be more attracted to chlorine. The electron cloud will be more distorted towards chlorine => The chlorine end is relatively negative and the carbon is relatively positive, electron deficient. δ+C -- δ-Cl

What does the electronegativity value of an atom depend on?

1. Nuclear charge 

2. Distance between nucleus and outer shell electrons. 

3. The shielding of the nucleus charge by electrons in the inner shells.

Explain how the carbon-hydrogen bond (such as in CH₄) differs from the nitrogen-hydrogen bond (such as in NH₃) in terms of the bond polarity.

The nitrogen-hydrogen bond is more polar than carbon-hydrogen bond because the difference in electronegativity between the nitrogen and hydrogen is larger.

Which of these atoms is most electronegative?

A. Br

B. Mg

C. Cl

D. Li

The answer is C.

The electronegativity of an atom depends on the nuclear charge and the distance between the valence electrons and the nucleus. Thus, the electronegativity increase when we move to the right of the periodic table and will decrease when we move down the periods

A is incorrect because Br is below Cl in the group leading to the electronegativity being lower

B is incorrect because Mg is on the left side of the periodic table 

D is incorrect because Li is also on the left side of the periodic table

The electronegativity of aluminium is similar to:

A. Boron 

B. Carbon 

C. Lithium 

D. Beryllium

The answer is C.

The electronegativity of an atom depends on the nuclear charge and the distance between the valence electrons and the nucleus. Thus, the electronegativity increase when we move to the right of the periodic table and will decrease when we move down the periods

A is incorrect because Br is below Cl in the group leading to the electronegativity being lower

B is incorrect because Mg is on the left side of the periodic table 

D is incorrect because Li is also on the left side of the periodic table

Which of the following correctly describes the relationship between ionic bonding and electronegativity?

A. The more electronegative element in an ionic bond will lose electrons

B. An ionic bond is formed when there is a difference in electronegativity of above 2.0 between two atoms

C. An ionic bond is formed when both atoms have the same electronegativity

D. An ionic bond is formed when the difference in electronegativity between the two atoms is between 1.0 and 2.0

The answer is B.

The difference in electronegativity between the two atoms will govern the type of bond that is formed.

If the electronegativity are very similar, the bond then will be covalent which will be in between 1.0 and 2.0 whereas the atoms have a large difference which is above 2.0, an ionic bond ill form

A is incorrect because the more electronegative element in ionic bond will become negative by gaining electrons

C is incorrect because a covalent bond is formed instead.

D is incorrect because An ionic bond is formed when the difference in electronegativity between the two atoms is above 2.0

Which compound is the most ionic?

A. NaCl

B. KBr

C. MgBr₂

D. RbCl

The answer is D.

Electronegativity decreases down a group and increases when we move to the right in the periodic table. Therefore, the most ionic compound will be the one with the greatest difference in electronegativity between the two atoms.

A, B, C are incorrect because the difference in electronegativity between NaCl, KBr, MgBr₂, all less than RbCl

Which substance contains polar covalent bonds?

A. ethane

B. sulfur dichloride

C. calcium bromide

D. chlorine

The answer is B.

There is a difference in electronegativity between two atoms S and Cl and Cl is more electronegative than S

A is incorrect because the C-H bond only has a small difference in electronegativity

C is incorrect there is a large difference in electronegativity and this is ionic bond

D is incorrect because chlorine has the same electronegativity