Sunday, February 27, 2011

Lewis Structure

The Lewis Structure for N2H4, with each pair of electron bonds circled in red. 

Monday, February 21, 2011

3-D Model of Hydrazine [N2H4]

This is a model of N2H4. The green spheres represent Nitrogen, the gray represent hydrogen, and the small yellow spheres represent the unshared electrons that Nitrogen has. The arrows in this picture represent the direction of a negative charge between two atoms (moving from a lower electronegativity charge to a higher electronegativity charge). 

Hydrazine can also be used for corrosion control in boilers and hot-water heating systems. It is the starting material for many derivatives, like foaming agents for plastics, antioxidants, fungicides, herbicides, and pharmaceuticals. Hydrazine is also used in photograph development techniques.


According to the U.S. Environmental Protection Agency, “Symptoms of acute (short-term) exposure to high levels of hydrazine may include irritation of the eyes, nose, and throat, dizziness, headache, nausea, pulmonary edema, seizures, and coma in humans.  Acute exposure can also damage the liver, kidneys, and central nervous system in humans.  The liquid is corrosive and may produce dermatitis from skin contact in humans and animals.  Effects to the lungs, liver, spleen, and thyroid have been reported in animals chronically (long-term) exposed to hydrazine via inhalation.  EPA has classified hydrazine as a Group B2, probable human carcinogen [cause of cancer]."

Types of Bonds in Hydrazine

The two types of bonds in the N2H4 molecule are found between Nitrogen and Nitrogen, and Nitrogen and Hydrogen. By using the elements’ electronegativity values and finding the difference between the two elements’ values, the type of bond can be determined.

      N           N                                                           N           H
     3.0         3.0                                                        3.0         2.2
             0                                                                         .8
Absolutely covalent                                            Moderately covalent
Non-polar                                                               Polar

Because the N-N bond has an electronegativity difference of 0, the bond is absolutely covalent. Also, it is a non-polar bond because N and N have the same electronegativity value. 

Because the N-H bond has an electronegativity difference of .8, the bond is moderately covalent. A polar bond occurs because one atom's electronegativity value has a larger electronegativity value than the other atom. In this case, the N atom has a larger electronegativity value than H, making the N-H bond polar.

To determine the nature of each bond, use this value line. The values on this line represents the differences between the bond's elements' electronegativity values. 

Intermolecular Forces of Attraction

There are three intermolecular forces of attraction: London dispersion, dipole dipole, and Hydrogen bonding. When a N2H4 molecule is near another N2H4 molecule, all three intermolecular forces of attraction occur between the two molecules.

London dispersion: a weak force of attraction between any 2 molecules (polar or nonpolar) that is created by temporary dipoles. These temporary dipoles are caused by the movement of electrons around both molecules.

Since London dispersion occurs between all molecules, an N2H4 molecule is attracted by the London dispersion force to another N2H4 molecule.

Dipole Dipole: an electrostatic attraction caused by the positive end of one dipole (a polar molecule) being attracted to the negative end of another dipole.

N2H4 is a polar molecule, there will be an dipole dipole attraction between two N2H4 molecules. The negative end of one N2H4, which is the end with nitrogen’s unshared electron pair, is attracted to the positive end of the other N2H4, which is the end with a hydrogen atom.

The Dipole Dipole force of attraction is shown in red by the dashed line between the positive end of one N2H4 molecule and the negative end of the other N2H4 molecule.

Hydrogen bonding: a special case of dipole dipole attraction. In hydrogen bonding, a temporary covalent bond forms between the hydrogen (H) of one molecule and the Oyxgen (O), Nitrogen (N) or Flourine (F) of an adjacent molecule.

Two molecules of N2H4 will have hydrogen bonding between them. The hydrogen atom in one molecule of N2H4 will form a temporary covalent bond with the Nitrogen of an adjacent N2H4 molecule. 

The temporary covalent bond that occurs in hydrogen bonding between two N2H4 molecule, shown in red with a  solid line between the Hydrogen of one N2H4 molecule the Nitrogen of the adjacent N2H4 molecule. 

Hydrazine: Polar molecule

A polar molecule is a molecule that has an uneven distribution of electrons. A non polar molecule is a molecule that has an even distribution of electrons. 

N2H4 is a polar molecule because the unshared electron pairs of the nitrogen atoms create an area on the molecule that is more negative than the space around the hydrogen atoms.

Also, only one line of symmetry can be drawn through the N2H4 dash model. If there is only one line of symmetry, the molecule is polar. 

The dash model for N2H4 with the one line of symmetry, shown in red. Note the negative area near the Nitrogens' unshared electron pairs and the positive areas around the Hydrogens, shown in purple.