LAB: SHAPES OF COVALENT MOLECULES & POLARITY

Introduction:

The most common chemical bond between two atoms is a covalent bond. The covalent bond consists of a pair of shared electrons, one from each atom. If this pair of electrons is shared between two atoms of equal electro negativities, the bond would be called a nonpolar covalent bond. However, in most cases, the pair of electrons is shifted toward the more electronegative element. A partial negative charge results on one side of the bond and a partial positive charge on the other. This type of covalent bond is called polar covalent.

Molecules composed of covalently bonded atoms may also be polar or nonpolar. For the molecule to be polar, it must, of course, have polar bonds. But the key factor for determining the polarity of a molecule is its shape. If the polar bonds (dipoles) are symmetrical around the central atom, they offset each other and the resulting molecule is nonpolar. However, if the dipoles are not symmetrical around the central atom, the electrons will be pulled to one end of this molecule and the resulting molecule is polar.

Objectives:

(1) Predict each molecule’s shape using your knowledge of hybridization.

(2) Predict each molecule’s polarity on the basis of its shape.

Equipment:

Paper and pencil

Procedure:

1. Prepare a data table according to the directions in the Analysis section below.

2. Complete your data table using the following compounds:

1. H25. SO3 9. CH413. CH3Cl

2. HBr6. CO2 10. HClO14. HCOOH

3. H2O7. H2CO 11. O215. CO32-

4. NH38. C2H2 12. AlH316. NH4+

Analysis:

Prepare a table for recording data for each of the 16 molecules. Include the following in your table: the formula, the Lewis dot structure, shared electron pairs, unshared electron pairs, total electron pairs, bonding orbitals, molecular shape, structural formula, and polarity. Use the table below as a guide:

Formula / Lewis
Structure / Shared
e-Pairs / Unshared
e- Pairs / Total
e-Pairs / Molecular Shape / Structural Formula / Polarity
HCl / H – Cl : / 1 / 0 / 1 / Linear / H – Cl / Polar

Further Investigations:

1. On the basis of this experiment and your classwork, predict the

a. type of bondingb. molecular shapec. molecular polarity

for each of the following compounds (construct a table):

(1) HBr(3) BaCl2(5) CI4

(2) SCl2(4) NH3(6) AlH3

2. Calculate the electronegativity difference and indicate the type of bond for

the following attractions:

(a) Na - Br(c) Se – O(e) Mg – Cl

(b) C - H(d) Br – Br(f)Al - I

3. What does the term isomer mean?

Key

Formula / Lewis
Structure / Shared
e-Pairs / Unshared
e- Pairs / Total
e-Pairs / Molecular Shape / Structural Formula / Polarity
HCl / / 1 / 0 or 3 / 1 or 4 / Linear / H – Cl / Polar
HBr / / 1 / 0 or 3 / 1 or 4 / Linear / H – Br / Polar
H2O / / 2 / 2 / 4 / Bent / / Polar
NH3 / / 3 / 1 / 4 / Trigonal Pyramidal / / Polar
SO3 / / 3 / 0 / 3 / Trigonal Planar / / Non
Polar
CO2 / / 2 / 2 / 4 / Linear / / Polar
H2CO / / 3 / 0 / 3 / Trigonal Planar / / Polar
C2H2 / / 2 / 0 / 2 / Linear / / Non
Polar
CH4 / / 4 / 0 / 4 / Tetra
hedral / / Non
Polar
HClO / / 2 / 2 / 4 / Bent / / Polar
O2 / / 2 / 2 / 4 / Linear / O – O / Non
Polar
AlH3
Ionic / / Ionic / Ionic / Ionic / Crystal
Lattice / / Ionic
CH3Cl / / 4 / 0 / 4 / Tetra
hedral / / Polar
HCOOH
Omit / / 3 / 0 / 3 / Trigonal Planar / / Polar
CO32- / / 3 / 0 / 3 / Trigonal Planar / / Non
Polar
NH4+ / / 4 / 0 / 4 / Tetra
hedral / / Non
Polar

Further Investigation

1. On the basis of this experiment and your classwork, predict the

a. type of bondingb. molecular shapec. molecular polarity

for each of the following compounds (construct a table):

(1) HBr(3) BaCl2(5) CI4

(2) SCl2(4) NH3(6) AlH3

Compound / Bond
Type / Molecular
Shape / Polarity
HBr / Covalent / Linear / Polar
SCl2 / Covalent / Bent / Polar
BaCl2 / Ionic / Crystal Lattice / Ionic
NH3 / Covalent / Trigonal Pyramidal / Polar
CI4 / Covalent / Tetrahedral / Non-Polar
AlH3 / Ionic / Crystal Lattice / Ionic

2. Calculate the electronegativity difference and indicate the type of bond for

the following attractions:

(a) Na - Br(c) Se – O(e) Mg – Cl

(b) C - H(d) Br – Br(f)Al - I

Elements / Electronegativity
Difference / Bond Type
Na - Br / Ionic
C - H / Covalent (Non-Polar)
Se – O / Covalent (Polar)
Br – Br / Covalent (Non-Polar)
Mg – Cl / Ionic
Al - I / Ionic

3. What does the term isomer mean?

Any of two or more compounds, radicals, or ions that contain the same number of atoms of the same elements but differ in structural arrangement and properties.

Example