Question

Hydrazine \(\left(\mathrm{H}_{2} \mathrm{NNH}_{2}\right),\) hydrogen peroxide \((\mathrm{HOOH}),\) and water \(\left(\mathrm{H}_{2} \mathrm{O}\right)\) all have exceptionally high surface tensions compared with other substances of comparable molecular weights. (a) Draw the Lewis structures for these three compounds. (b) What structural property do these substances have in common, and how might that account for the high surface tensions?

Short answer

The common structural property among hydrazine \(\mathrm{(H_2NNH_2)}\), hydrogen peroxide \(\mathrm{(HOOH)}\), and water \(\mathrm{(H_2O)}\) is the presence of polar bonds due to electronegativity differences and the ability to form hydrogen bonds. This accounts for their high surface tensions compared to other substances of similar molecular weights.

Step-by-step solution

Drawing Lewis structures for hydrazine, hydrogen peroxide, and water

To draw the Lewis structures for these compounds, we need to determine the distribution of valence electrons in the molecules. For hydrazine (H2NNH2): 1. Count the total number of valence electrons: 2 Nitrogens (each has 5 valence electrons) + 4 Hydrogens (each has 1 valence electron) = 10+4 = 14 valence electrons. 2. Place the N atoms in the center and H atoms around each N atom. 3. Distribute the electrons between the center atoms and the surrounding atoms to create single bonds. 4. Fill the octets on the outer atoms (H in this case). 5. If necessary, create multiple bonds to satisfy the octets on the central atoms. Hydrazine Lewis Structure: ``` H - N - N - H | | H H ``` For hydrogen peroxide (HOOH): 1. Count the total number of valence electrons: 2 Oxygens (each has 6 valence electrons) + 2 Hydrogens (each has 1 valence electron) = 12+2 = 14 valence electrons. 2. Place the O atoms in the center and H atoms around each O atom. 3. Distribute the electrons between the center atoms and the surrounding atoms to create single bonds. 4. Fill the octets on the outer atoms (H in this case). 5. If necessary, create multiple bonds to satisfy the octets on the central atoms. Hydrogen Peroxide Lewis Structure: ``` H - O - O - H ``` For water (H2O): 1. Count the total number of valence electrons: 1 Oxygen (has 6 valence electrons) + 2 Hydrogens (each has 1 valence electron) = 6+2 = 8 valence electrons. 2. Place the O atom in the center and H atoms around the O atom. 3. Distribute the electrons between the center atom and the surrounding atoms to create single bonds. 4. Fill the octets on the outer atoms (H in this case). Water Lewis Structure: ``` O / \ H H ```

Identifying the common structural property and its relation to high surface tension

After examining the Lewis structures of hydrazine, hydrogen peroxide, and water, we can observe that all three compounds have polar bonds due to electronegativity differences between the atoms (N-H, O-H). Additionally, all three molecules contain highly electronegative atoms (N, O), which can form hydrogen bonds with each other. The strong hydrogen bonds result in an increased surface tension in these molecules as compared to other substances with similar molecular weights. The high electronegativity and strong hydrogen bonding contribute to the increased surface tension of these compounds. So, the common structural property among hydrazine, hydrogen peroxide, and water is the presence of polar bonds and the ability to form hydrogen bonds. This property accounts for their high surface tensions compared to other substances of similar molecular weights.