Regents Chemistry Exam Explanations August 2009

Bond energy is the amount of energy required to break a chemical bond. The table below gives a formula and the carbon-nitrogen bond energy for selected nitrogen compounds.

59 Describe, in terms of electrons, the type of bonding between the carbon atom and the nitrogen atom in a molecule of methanamine. [1]

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Electrons are shared

(2 nonmetals=Covalent=sharing electrons)

60 Identify the noble gas that has atoms in the ground state with the same electron configuration as the nitrogen in a molecule of isocyanic acid. [1]

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Neon (Ne)

(Nitrogen gets 3 more electrons due to the 3 bonds and ends up with 10 electrons like Neon)

61 State the relationship between the number of electrons in a carbon-nitrogen bond and carbon-nitrogen bond energy. [1]

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As the number of shared electrons in a carbon-nitrogen bond increases, the bond energy increases.

Less energy is required to break a single carbon-nitrogen bond than to break a triple carbon-nitrogen bond.

62 Explain, in terms of charge distribution, why a molecule of hydrogen cyanide is polar. [1]

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The molecule has an asymmetrical charge distribution.

The molecule has an unequal distribution of charge.

(SNAP=symmetrical nonpolar asymmetrical polar)

63 A 3.2-gram sample of air contains 0.000 74 gram of hydrogen cyanide. Determine the concentration, in parts per million, of the hydrogen cyanide in this sample. [1]

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230 ppm

(0.00074g/(3.2g) x 1,000,000