Question

A toxic cloud covered Bhopal, India, in December 1984 when water leaked into a tank of methyl isocyanate, and the product escaped into the atmosphere. Methyl isocyanate is used in the production of many pesticides. Draw the Lewis structures for methyl isocyanate, \(\mathrm{CH}_{3} \mathrm{NCO}\), including resonance forms. The skeletal structure is

Short answer

The Lewis structures for methyl isocyanate (CH₃NCO), including resonance forms, are: Structure 1: O || H - C - H - N - C - H | H Structure 2: O || H - C - H - N - C - O - - | H These two structures represent the possible configurations of methyl isocyanate.

Step-by-step solution

Count the valence electrons in the molecule

The total number of valence electrons in a molecule can be calculated by adding the valence electrons of each atom. In methyl isocyanate (CH₃NCO), we have: - Carbon (C): Valence electrons: 4 Number of atoms: 2 (one in CH₃ and one in NCO) Total: 4 * 2 = \(8\) - Hydrogen (H): Valence electrons: 1 Number of atoms: 3 (all in CH₃) Total: 1 * 3 = \(3\) - Nitrogen (N): Valence electrons: 5 Number of atoms: 1 Total: 5 * 1 = \(5\) - Oxygen (O): Valence electrons: 6 Number of atoms: 1 Total: 6 * 1 = \(6\) Adding these values together gives us the total number of valence electrons in the molecule: \(8 + 3 + 5 + 6 = 22\)

Distribute the electrons in the central atoms

Place the least electronegative atom (or the atom that can make the most bonds) in the center. In this case, nitrogen (N) is the central atom in the NCO group. Now distribute the electrons to form bonds: - For the CH₃ group, each of the three hydrogens will form a single bond with the carbon atom. This will use up \(6\) electrons (3 bonds * 2 electrons each = 6 electrons). - For the NCO group, bond N to C and C to O. This will initially use up \(4\) electrons (2 bonds * 2 electrons each = 4 electrons).

Complete the octets and identify possible resonance structures

Now complete the octets for atoms in the NCO group: - For nitrogen (N), add two more electrons to form a lone pair. Nitrogen will have three bonding electrons (one bond with C) and two non-bonding electrons. - For oxygen (O), add four more electrons to form two lone pairs. Oxygen will have two bonding electrons (one bond with C) and four non-bonding electrons. - For carbon (C), it currently has two bonding electrons (from the initial bond to N and O). We can form a resonance structure by shifting the electrons in a double bond between N and C or C and O: Structure 1 (Double bond between N and C): Draw a double bond between N and C, which will leave two non-bonding electrons on oxygen (O). In this case, Nitrogen has four bonding electrons and no non-bonding electrons, Carbon has four bonding electrons and no non-bonding electrons, and Oxygen has two bonding and four non-bonding electrons. Structure 2 (Double bond between C and O): Draw a double bond between C and O, which will leave nitrogen (N) with a lone pair (two non-bonding electrons). In this case, Nitrogen has three bonding electrons and two non-bonding electrons, Carbon has four bonding electrons and no non-bonding electrons, and Oxygen has four bonding and two non-bonding electrons.

Draw the Lewis structures including resonance forms

Now we can draw the Lewis structures for methyl isocyanate (CH₃NCO), including resonance forms: Structure 1: O || H - C - H - N - C - H | H Structure 2: O || H - C - H - N - C - O - - | H These two structures, including resonance forms, represent the possible configurations of methyl isocyanate (CH₃NCO).

Key concepts

Valence Electrons

Valence electrons are the electrons in the outermost shell of an atom and they play a key role in chemical bonding and molecule formation. Understanding how to count and use these electrons is crucial for predicting how atoms will interact with each other.

In the case of methyl isocyanate, as explained in the step-by-step solution, the total count of valence electrons is vital for constructing the proper Lewis structure. The carbon atoms have four valence electrons each, hydrogen atoms have one, nitrogen has five, and oxygen has six. Adding these up correctly will ensure that all the atoms in the molecule can achieve full outer shells or stable configurations, abiding by the octet rule—where atoms strive to have eight electrons in their valence shell to achieve stability, much like noble gases.

By keeping track of these electrons during the drawing of Lewis structures, one can predict the types of bonds that will form. This not only assists in creating accurate representations of chemical compounds but also helps in understanding the properties and reactivity of such compounds.

Lewis Structures Resonance

Resonance in chemistry refers to situations where a molecule can be represented by two or more valid Lewis structures. These structures, known as resonance forms, are not isomers of the molecule but depict the same molecule with electrons in different positions. Resonance is a concept used to describe the delocalization of electrons within certain molecules, especially those with conjugated systems or multiple bonding possibilities.

In methyl isocyanate, resonance occurs between the nitrogen and carbon atoms and the carbon and oxygen atoms. These variations are equally valid representations of the molecule's structure. By illustrating the resonance forms, chemists can get a better understanding of molecule stability and the distribution of electron density. In educational content, it's important to clearly show each resonance form and explain that the actual structure of the molecule is a hybrid of these forms, which provides stability to the molecule. This concept helps clarify how molecules like methyl isocyanate can have bonds that are intermediate between single and double bonds, affecting their chemical behavior.

Chemical Bonding

Chemical bonding is the force that holds atoms together in molecules and compounds. The basic principle of chemical bonding is that atoms combine in such a way that they achieve a more stable electron configuration. There are several types of chemical bonds, including ionic, covalent, and metallic bonds.

In the Lewis structures for methyl isocyanate, the covalent bonds are clearly illustrated. Covalent bonding involves the sharing of valence electrons between atoms, and it is a common type of bonding in organic molecules. Methane isocyanate includes single bonds, as seen between the carbon and hydrogen atoms, as well as the potential for double bonds between carbon-nitrogen and carbon-oxygen pairs, as depicted in the resonance structures.

An accurate Lewis structure incorporates all potential bonding scenarios to fully represent the molecule's structure. In educational content, emphasis should be placed on how electrons are shared to form covalent bonds, how to complete the octets, and how double bonds can form and be represented in resonance structures. Understanding chemical bonding is fundamental for students because it is closely linked to how molecules interact with one another and react, which therefore influences the molecule's properties and functions.