Question

Using Lewis symbols and Lewis structures, make a sketch of the formation of \(\mathrm{NCl}_{3}\) from \(\mathrm{N}\) and \(\mathrm{Cl}\) atoms, showing valence- shell electrons. (a) How many valence electrons does N have initially? (b) How many bonds Cl has to make in order to achieve an octet? (c) How many valence electrons surround the \(\mathrm{N}\) in the \(\mathrm{NCl}_{3}\) molecule? (d) How many valence electrons surround each Cl in the \(\mathrm{NCl}_{3}\) molecule? (e) How many lone pairs of electrons are in the \(\mathrm{NCl}_{3}\) molecule?

Short answer

(a) Nitrogen has an initial number of 5 valence electrons. (b) Each chlorine atom needs to create 1 bond to achieve an octet. (c) In the NCl₃ molecule, there are 6 valence electrons surrounding the nitrogen atom. (d) There are 8 valence electrons surrounding each chlorine atom in the NCl₃ molecule. (e) There are 10 lone pairs of electrons in the NCl₃ molecule.

Step-by-step solution

(Drawing Lewis symbols for N and Cl atoms)

First, we need to draw the Lewis symbols for the nitrogen (N) and chlorine (Cl) atoms. To do this, we need to show the valence electrons of each atom around their corresponding symbols. Nitrogen has 5 valence electrons, while chlorine has 7 valence electrons. Nitrogen (N): \[\cdot N \cdot \] Chlorine (Cl): \[\odot Cl \ominus \]

(Drawing the Lewis structure for NCl₃ )

In the next step, we will draw the Lewis structure for NCl₃. We need to show how the nitrogen atom shares its valence electrons with three chlorine atoms to form three single (covalent) bonds. This is done by pairing one valence electron from N with one from each of the three Cl atoms: \[ \chemfig{ Cl% <- Atom 1 -[,1.5]@{bb1}N% <- Atom 2 (-[,1.5]<-:[:135]Cl)% <- Atom 3 (-[,1.5]<-[:45]Cl)% <- Atom 4 } \] Here, we can see that the nitrogen atom is connected to three chlorine atoms by single bonds. Now, we will proceed to answer each of the given questions:

(a) Number of valence electrons in the nitrogen atom initially)

As mentioned earlier, a nitrogen atom has 5 valence electrons initially.

(b) How many bonds Cl has to make in order to achieve an octet)

Each chlorine atom has 7 valence electrons initially. To achieve an octet (eight electrons in the outermost shell), each chlorine atom must form 1 bond with another atom, such as nitrogen in this case.

(c) Valence electrons surrounding N in the NCl₃ molecule)

In the NCl₃ molecule, the nitrogen atom forms three single bonds with the three chlorine atoms. Since each bond is formed by sharing a pair of electrons, there are a total of 6 valence electrons surrounding the nitrogen atom.

(d) Valence electrons surrounding each Cl in the NCl₃ molecule)

In the NCl₃ molecule, each chlorine atom forms a single bond with the nitrogen atom and also has 3 lone pairs of electrons. A single bond consists of 2 shared electrons, and each lone pair has 2 electrons. Hence, there are 2 (shared) + 2*3 (lone pairs) = 8 valence electrons surrounding each chlorine atom in the NCl₃ molecule.

(e) Number of lone pairs of electrons in the NCl₃ molecule)

In the NCl₃ molecule, the nitrogen atom has 1 lone pair of electrons, while each of the three chlorine atoms has 3 lone pairs of electrons. Thus, there are 1 + 3*3 = 10 lone pairs of electrons in the NCl₃ molecule.

Key concepts

Valence Electrons

Valence electrons are the outermost electrons of an atom, crucial for forming bonds between atoms in a molecule. These electrons determine how an atom interacts with others to form chemical bonds.
For example, nitrogen (N) and chlorine (Cl) must form the compound \( \mathrm{NCl}_{3} \).
Here are some key points to remember:

• Nitrogen (N) has 5 valence electrons. These electrons are the ones it uses to bond with other atoms.
• Chlorine (Cl) has 7 valence electrons. To achieve the stable octet, a Cl atom seeks one more electron.

Recognizing how many valence electrons an atom possesses helps predict how it can bond to form compounds like \( \mathrm{NCl}_{3} \). Ultimately, these valence electrons are the first step towards understanding molecular shapes and interactions.

Covalent Bonds

Covalent bonds are essential for the formation of stable molecules. Unlike ionic bonds, which involve the transfer of electrons, covalent bonds form when two atoms share one or more pairs of electrons. This sharing allows each atom to attain an electron configuration similar to that of the nearest noble gas, making them more stable.
In \( \mathrm{NCl}_{3} \), nitrogen forms covalent bonds with three chlorine atoms.
Some important points:

• A covalent bond involves a mutual sharing of electrons between atoms. Each shared pair contributes to a stable electron arrangement.
• In \( \mathrm{NCl}_{3} \), nitrogen shares its electrons with chlorine atoms to form three single covalent bonds, creating a stable molecule.

Understanding covalent bonding is vital as it affects the physical properties and reactivity of molecules.

Lone Pairs

Lone pairs are pairs of valence electrons that are not involved in bonding. They are found in the outer shell of an atom and can affect the shape and reactivity of a molecule. Recognizing lone pairs is important in predicting molecular geometry and polarity.
In the \( \mathrm{NCl}_{3} \) molecule, lone pairs play a significant role in its structure:

• Nitrogen in \( \mathrm{NCl}_{3} \) has 1 lone pair of electrons that do not take part in the bonding but affect the molecule's shape and angle.
• Each chlorine atom in \( \mathrm{NCl}_{3} \) has 3 lone pairs of electrons, contributing to the atom's octet and further affecting the molecule's behavior.

Lone pairs can impact the molecular geometry, leading to differences in bond angles and molecular polarity, making them a key concept in understanding molecular structures.