Chapter 4, Problem 79P

Interpretation Introduction

(a)

Interpretation:

Lone pairs should be added where needed and the total number of valence electrons in glycine should be counted.

Concept Introduction:

Valence electrons are the electrons reside in valence shell of an atom and valence electrons are the ones which participate in bonding. In main group elements, group number equals to the number of valence electrons. The sum gives the total number of valence electrons in a molecule.

Interpretation Introduction

(b)

Interpretation:

The shape around the four indicated atoms should be determined.

Concept Introduction:

To determine the shape around a given atom, first number of groups around that atom should be determined. Group is referred to an atom or a lone pair. Then the shape is determined by valence shell electron pair repulsion theory(VSEPR). According to this theory the groups around an atom are as far away from each other as possible in the most stable arrangement of a molecule.

Interpretation Introduction

(c)

Interpretation:

All polar bonds in glycine should be labeled.

Concept Introduction:

The electronegativity difference can be used to differentiate bonds as polar, polar covalent and ionic bonds in different compounds.

If the electronegativity difference between two atoms is less than 0.5, the bond is nonpolar in which electrons are equally shared. If the electronegativity difference is between 0.5 − 1.9, the bond is polar covalent, in which electrons are unequally shared, the electron density is more towards electronegative atom. For electronegativity difference more than 1.9, the bond is ionic, in which electrons has been transferred from the less electronegative atom to more electronegative atom.

Interpretation Introduction

(e)

Interpretation:

Whether the glycine is a polar molecule should be determined.

Concept Introduction:

Polarity of a molecule depends on the individual bonds and the overall shape. If a molecule has no polar bonds, then the molecule is nonpolar. If the molecule has one polar bond, then the molecule is considered to be polar. If a molecule has more than one polar bond, the shape of the molecule determines the polarity of the molecule. If the bond dipoles do not cancel, the molecule is polar. If they get cancelled, the molecule is non-polar.