Problem 150 - Chemistry The Science in Context

Question

Draw all resonance forms for the molecules NSF and HBS where \(S\) and \(B\) are the central atoms, respectively. Include possible ionic structures for NSF.

Step-by-Step Solution

Answer

Question: Draw all resonance forms for the molecules NSF and HBS, and include possible ionic structures for NSF. Answer: For NSF, there are three resonance structures: 1. Original structure: N-S double bond, S-F single bond, with S having a lone pair and N having two lone pairs. 2. Resonance structure 1: N-S triple bond, S-F single bond, S has a positive charge, and N has a negative charge. 3. Resonance structure 2: N-S double bond, S-F double bond, S has a positive charge, and F has a negative charge. Two ionic structures for NSF are: 1. Ionic structure 1: N-S triple bond, S-F single bond, N has a +1 charge, S has no charge, and F has a -1 charge. 2. Ionic structure 2: N-S double bond, S-F double bond, N has a +1 charge, S has a +1 charge, and F has a -2 charge. For HBS, there are no resonance structures as there are no lone pairs involved in the bonding atoms.

Step 1: Draw the Lewis structures of NSF and HBS

Start by drawing the Lewis structures of both molecules, ensuring that the central atoms (S for NSF and B for HBS) have complete octets. For NSF: N has 5 valence electrons, S has 6 valence electrons, and F has 7 valence electrons. A single bond between each pair of atoms (N-S and S-F) will result in an octet for each atom. For HBS: H has 1 valence electron, B has 3 valence electrons, and S has 6 valence electrons. A single bond between each pair of atoms (H-B and B-S) will result in an octet for each atom, except for boron, which is fine having only six electrons due to its position in the periodic table.

Step 2: Draw resonance structures for NSF

For NSF, we can see that there is a possibility for resonance due to the presence of lone electron pairs in N and S. We will draw the resonance structures as follows: 1. Original structure: N-S double bond, S-F single bond, with S having a lone pair and N having two lone pairs. 2. Resonance structure 1: Move an electron pair from N (in a lone pair) to a N-S bond, now N-S has a triple bond, giving S a positive charge, and N has a negative charge. 3. Resonance structure 2: Move an electron pair from S (in S-F bond) to F, now S-F single bond to S-F double bond, giving S a positive charge, and F a negative charge.

Step 3: Draw resonance structures for HBS

For HBS, there is no possibility for resonance structures, as there are no lone pairs involved in the bonding atoms.

Step 4: Draw possible ionic structures for NSF

In the case of NSF, we can create ionic forms by considering the movement of one or both lone electron pairs from N to F: 1. Ionic structure 1: Move an electron pair from N (in a lone pair) to S, now N has a triple bond to S and there's a single bond between S and F. N has a +1 charge, S has no charge, and F has a -1 charge. 2. Ionic structure 2: Move an electron pair from S (in S-F bond) to F, now N has a double bond to S and there's a double bond between S and F. N has a +1 charge, S has a +1 charge, and F has a -2 charge. Now, you have found all the resonance and ionic forms for the NSF and HBS molecules.

Key Concepts

Lewis structures

Lewis structures are a great tool to visualize how atoms within a molecule are bonded together and where the electrons are located. These diagrams show the arrangement of the atoms, the connectivity between them, and the distribution of valence electrons.

To draw a Lewis structure, start by counting the total number of valence electrons for the molecule. Then, place the atoms around the central atom, which is usually the least electronegative. Create bonds, typically shown as lines, between the central atom and surrounding atoms. Use the remaining electrons to complete the outer octets of the atoms, ensuring octet rule satisfaction if applicable.

• Central Atom: Usually the least electronegative, other than hydrogen.
• Valence Electrons: Total should match the molecule's electron count.
• Bond Lines: Represent shared electron pairs (bonds).

In molecules like NSF and HBS, use the knowledge of how many bonds each atom can form based on its electron configuration to guide your drawing.

Valence electrons

Valence electrons are the outermost electrons of an atom and play a crucial role in chemical bonding. They are responsible for the chemical properties of the element as these electrons can be gained, lost, or shared in a bond.

In the context of Lewis structures and resonance, it’s important to know the number of valence electrons when predicting how an atom will bond and form stable compounds. For instance, in NSF, nitrogen (N) provides 5 valence electrons, sulfur (S) offers 6, and fluorine (F) gives 7.

• Determine total valence electrons for accuracy in diagrams.
• Use them to satisfy the octet or duplet rule (for hydrogen).
• Understanding electron sharing helps in creating correct structures.

Remember, certain elements like boron in HBS may not obey the octet rule due to their position in the periodic table.

Ionic structures

Ionic structures represent a form of chemical bonding that occurs when one atom donates valence electrons to another atom, creating ions. This type of bonding is different from covalent, where electrons are shared.

In molecules that are primarily covalent, like NSF, ionic forms might not be as common but are still notable possibilities. These might occur in resonance structures where electron pairs shift, creating temporary ionic charges.

• Ions are formed when atoms gain or lose electrons.
• Occur due to electron pair shifts in some resonance structures.
• Ionic charges arise and can provide alternative resonance forms.

Understanding ionic structures is essential for predicting molecule stability and the presence of full positive or negative charges in some resonance forms.

Molecular bonds

Molecular bonds are the connections between atoms that make up molecules. They hold the atoms together and determine the molecule's properties and behavior.

The main types of molecular bonds are covalent, where electrons are shared equally or unequally between atoms, and ionic, where electrons are transferred from one atom to another. The type of bond impacts the molecule's shape, polarity, and reactivity. In Lewis structures such as NSF and HBS, the molecular bonds are primarily covalent, as shown by shared electron pairs.

• Covalent Bonds: Involve sharing of electrons between atoms.
• Ionic Bonds: Involve electron transfer to form charged ions.
• Bonding affects molecule's structure and chemical behavior.

Recognizing the type of bond between atoms within a molecule helps predict how the molecule will interact with others and can guide the drawing of accurate resonance and ionic structures.