Problem 34 - Chemistry The Central Science

Question

Use Lewis symbols and Lewis structures to diagram the formation of \(\mathrm{PF}_{3}\) from \(\mathrm{P}\) and \(\mathrm{F}\) atoms, showing valence- shell electrons. (a) How many valence electrons does P have initially? (b) How many valence electrons does each F have initially? ( c) How many valence electrons surround the Pin the PF_ \(_{3}\) molecule? (d) How many valence electrons surround each \(\mathrm{F}\) in the \(\mathrm{PF}_{3}\) molecule? (e) How many bonding pairs of electrons are in the \(\mathrm{PF}_{3}\) molecule?

Step-by-Step Solution

Answer

In summary, the Lewis structure of \(\mathrm{PF}_{3}\) is formed by combining a phosphorus (P) atom with 3 fluorine (F) atoms, sharing electrons to create covalent bonds. Initially, P has 5 valence electrons, and each F atom has 7 valence electrons. In the \(\mathrm{PF}_{3}\) molecule, 8 valence electrons surround the P atom, and 8 valence electrons surround each F atom. The molecule has 3 bonding pairs of electrons, represented by the single covalent bonds between P and F atoms.

Step 1: Determine the Lewis symbols for P and F atoms

First, we need to determine the Lewis symbols for the P and F atoms. The Lewis symbol represents the symbol of an element and its valence electrons as dots surrounding the symbol. P has 5 valence electrons (it is in group 15 of the periodic table), and F has 7 valence electrons (it is in group 17). Therefore, their Lewis symbols are: P: :P⋅⋅ F: :F: Notice that there's a pair of dots on the left side of both P and F.

Step 2: Draw the Lewis structure for \(\mathrm{PF}_3\)

To draw the Lewis structure for \(\mathrm{PF}_{3}\), we first need to combine the P atom with 3 F atoms. The 3 F atoms will each share one of their unpaired electrons with the P atom to form a covalent bond, as shown below: :F: | .:P:---:F: | :F:

Step 3: Answer the questions based on the Lewis structure

Now that we have the Lewis structure of \(\mathrm{PF}_3\), we can answer the questions: (a) P has 5 valence electrons initially, as mentioned in Step 1. (b) Each F atom has 7 valence electrons initially, as mentioned in Step 1. (c) In the \(\mathrm{PF}_{3}\) molecule, P atom is surrounded by 8 valence electrons (2 lone pairs and 6 shared electrons). (d) Each F atom in \(\mathrm{PF}_3\) is surrounded by 8 valence electrons (6 from their lone pairs and 2 from the shared pair with P). (e) There are 3 bonding pairs of electrons in the \(\mathrm{PF}_3\) molecule, as seen in the Lewis structure with the 3 single covalent bonds between P and F atoms.

Key Concepts

Valence Electrons

Valence electrons are the electrons in the outermost shell of an atom. They play a key role in chemical bonding since they are the ones involved in forming bonds.
Atoms tend to react with each other to achieve a full valence shell, similar to noble gases, which is often eight electrons, known as the octet rule.
These electrons are depicted as dots around the symbol of an element in Lewis structures.

• P, from group 15, has 5 valence electrons.
• F, from group 17, has 7 valence electrons.

In the formation of \(\text{PF}_3\), both P and F atoms share their valence electrons to achieve full outer shells and more stability.

Covalent Bond

A covalent bond is formed when two atoms share a pair of electrons. This type of bond allows each of the atoms involved to reach a full valence shell, thus stabilizing the molecule.
In Lewis structures, covalent bonds are represented by lines connecting two atoms. Each line represents a pair of shared electrons.
In the molecule \(\text{PF}_3\):

• P shares one electron with each F atom, forming three single covalent bonds.
• Each of these bonds involves a pair of shared electrons - one from P and one from F.

Through sharing, P fulfills its need for more electrons to complete its octet. Similarly, each F atom achieves an octet by sharing with P.

Chemical Bonding

Chemical bonding occurs as atoms aim to achieve greater stability. This is usually by filling their outermost electron shells, leading to the formation of molecules.
There are various types of chemical bonds, with covalent bonds being a primary type for nonmetals like \(\text{P}\) (phosphorus) and \(\text{F}\) (fluorine).
In the \(\text{PF}_3\) molecule:

• Each P atom needs to form bonds with three F atoms to use its five valence electrons effectively.
• These interactions lead to the creation of three covalent bonds.
• As a result, P achieves a pseudo-noble gas configuration, surrounded by eight electrons, making it more stable.

Overall, chemical bonding is a central topic in understanding how atoms combine to form molecules and the resulting properties of those compounds.