Chapter 5.10, Problem 5QQ

Interpretation Introduction

Interpretation:

The fractional charge that is present on a more electronegative atom in a polar covalent bond has to be chosen from the given options.

Concept Introduction:

Close relationship between ionic and covalent bonding models becomes apparent if the bond polarity and electronegativity is considered.  Electronegativity is the measure of relative attractive for the shared pair of electrons in a bond.  Higher the electronegative value for an atom, the more it attracts the shared pair of electrons towards itself.

In Periodic table, when moving from left to right in a period, the electronegativity value increases.  While moving from top to bottom within group, the electronegativity value decreases.  Nonmetals have higher electronegativity values than metals.  Metals gives electrons and nonmetals accepts electrons.

Bond polarity is the degree of inequality in the electron pair sharing between two atoms in a chemical bond.  If the electrons are equally shared between two atoms then it is known as nonpolar covalent bond.  If the electrons are unequally shared between two atoms means then it is known as polar covalent bond.  The more electronegative atom pulls the shared pair of electrons towards itself resulting in fractional negative charge over it while the other atom gets a fractional positive charge.  The fractional negative charge is depicted by using the symbol ${\delta }^{-}$ and fractional positive charge is depicted using the symbol ${\delta }^{+}$.  The direction of polarity for a polar covalent bond can also be represented by an arrow in which a perpendicular line is passing through the tail.  The head is at the more electronegative atom in the bond.

The ionic and covalent bonds can be identified by using the electronegativity difference between the atoms that are bonded together.

• Bonds that are formed between two similar electronegative atoms are known as nonpolar covalent bonds.  The electronegativity difference has to be 0.4 or less.
• The bonds that have electronegativity difference greater than 0.4 and lesser than 1.5 are known as polar covalent bonds.
• If the electronegativity difference is more than 2.0, then the bond is considered to be ionic.
• If the electronegativity difference is between 1.5 to 2.0, then the bond can be ionic or covalent depending upon the type of atoms that is bonded.  If the bond is between a metal and nonmetal, then it is ionic and if it is between two nonmetals then it is polar covalent.