Chapter U2.17, Problem 3E

(a)

Interpretation Introduction

Interpretation : The given pairs of atoms have to be arranged in order of increasing bond polarity and the trend is to be described.

Concept Introduction :

The tendency of an atom to attract shared electrons is called electronegativity. Chemists have assigned each atom a number called electronegativity value. This number represents the tendency of the atom to attract shared electrons. By comparing these numbers,one can compare the polarity of bonds.

Answer to Problem 3E

Bond polarities of given pairs of atoms are:

Li-F: 3.0

Na-F: 3.05

K-F: 3.16

Rb-F: 3.16

Cs-F: 3.19

Based on the bond polarities, the given pairs can be arranged as:

Li-F< Na-F< K-F<Rb-F< Cs-F

Trend- The bond polarity increases from top to bottom of the periodic table.

Explanation of Solution

The electronegativity scale is used to compare individual atoms. Atoms that are more electronegative attract bonded electrons more strongly than atoms with less electronegative value. This results in formation of a polar bond. As the difference in electronegativity increases, the bond polarity increases.

Li-F- From the electronegativity scale, electronegativity value of lithium is 0.98 and fluorine is 3.98. Difference in electronegativity value= 3.98-0.98=3.0

Na-F-From the electronegativity scale, electronegativity value of sodium is 0.93 and fluorine is 3.98. Difference in electronegativity value= 3.98-0.93=3.05

K-F- From the electronegativity scale, electronegativity value of potassium is 0.82 and fluorine is 3.98. Difference in electronegativity value= 3.98-0.82=3.16

Rb-F- From the electronegativity scale, electronegativity value of rubidium is 0.82 and fluorine is 3.98. Difference in electronegativity value= 3.98-0.82=3.16

Cs-F- From the electronegativity scale, electronegativity value of cesium is 0.79 and fluorine is 3.98. Difference in electronegativity value= 3.98-0.79=3.19

Trend- From the electronegativity values of metals, one see that the scale increase from bottom to top of the periodic table.Since all these metals are bonding with fluorine, the difference in their electronegativities increases from top to bottom. Hence, the bond polarity of Cs-F is highest and that of Li-F is lowest. This can be represented as:

Li-F< Na-F< K-F<Rb-F< Cs-F

(b)

Interpretation Introduction

Interpretation : The given pairs of atoms needs to be arranged in order of increasing bond polarity and the trend is to be described.

Concept Introduction :

The tendency of an atom to attract shared electrons is called electronegativity. Chemists have assigned each atom a number called electronegativity value. This number represents the tendency of the atom to attract shared electrons. By comparing these numbers we can compare the polarity of bonds.

Answer to Problem 3E

Bond polarities of given pairs of atoms are:

Mg-O: 2.13

P-S: 0.39

N-F: 0.94

K-Cl: 2.34

Al-N: 1.43

Based on the bond polarities, the given pairs can be arranged as:

P-S< N-F< Al-N< Mg-O< K-Cl

Trend- The bond polarity increases with increase in distance between elements on the periodic table. The more closer the elements are on the periodic table, the least strong will be the bond.

Explanation of Solution

The electronegativity scale is used to compare individual atoms. Atoms that are more electronegative attract bonded electrons more strongly than atoms with less electronegative value. This results in formation of a polar bond. As the difference in electronegativity increases the bond polarity increases.

Mg-O- From the electronegativity scale, electronegativity value of magnesium is 1.31 and oxygen is 3.44. Difference in electronegativity value= 3.44-1.31=2.13

P-S-From the electronegativity scale, electronegativity value of phosphorus is 2.19 and sulfur is 2.58. Difference in electronegativity value= 2.58-2.19=0.39

N-F- From the electronegativity scale, electronegativity value of nitrogen is 3.04 and fluorine is 3.98. Difference in electronegativity value= 3.98-3.04=0.94

K-Cl- From the electronegativity scale, electronegativity value of potassium is 0.82 and chlorine is 3.16. Difference in electronegativity value= 3.16-0.82=2.34

Al-N- From the electronegativity scale, electronegativity value of aluminium is 1.61 and nitrogen is 3.04. Difference in electronegativity value= 3.04-1.61=1.43

Trend- From the electronegativity values of atoms, we see that the closer the atoms are on the scale, the lesser is the bond polarity and farther they are, greater is the bond polarity as the difference in electronegativity value is more when the elements are farther apart. Hence, the bond polarity of K-Clis highest and that of P-Sis lowest. This can be represented as:

P-S< N-F< Al-N< Mg-O< K-Cl