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.

Step-by-Step Solution

Answer

To diagram the formation of $\mathrm{PF}_{3}$ from P and F atoms using Lewis symbols and Lewis structures, first determine the Lewis symbols for phosphorus (P) with 5 valence electrons and fluorine (F) with 7 valence electrons. In $\mathrm{PF}_{3}$, each fluorine atom shares one electron with the phosphorus atom, creating a single covalent bond between each pair of atoms (P-F). The resulting Lewis structure of phosphorus trifluoride ($\mathrm{PF}_{3}$) is: F | P -- F -- P -- F | | F F In this structure, the dashes (-) represent the covalent bonds formed between the phosphorus and fluorine atoms, each dash representing a shared electron pair. There are 3 single covalent bonds in $\mathrm{PF}_{3}$, with a total of 6 electrons involved in the bonding.

Step 1: Determine the Lewis symbols for individual atoms

First, we need to draw the Lewis symbols for the phosphorus and fluorine atoms. To do this, we need to know the number of valence electrons in each atom. Phosphorus has 5 valence electrons, and fluorine has 7 valence electrons. Represent these electrons as dots around the symbols for each element. Lewis symbol for phosphorus: P with 5 dots around it. Lewis symbol for fluorine: F with 7 dots around it.

Step 2: Combine the atoms to form a molecule

In PF₃, there is one phosphorus atom and three fluorine atoms. To form the molecule, each fluorine atom shares one electron with the phosphorus atom, creating a single covalent bond between each pair of atoms (P-F). After sharing one electron, each fluorine atom has fulfilled its octet and has 8 electrons surrounding it, while phosphorus has 8 electrons as well (3 from the fluorine atoms and 5 of its own).

Step 3: Draw the Lewis structure of the final molecule

When drawing the Lewis structure of PF₃, we need to show the electron pairs shared between the phosphorus and fluorine atoms and the remaining lone pair electrons on each atom. The Lewis structure of phosphorus trifluoride (PF₃) can be represented as: F | P -- F -- P -- F | | F F In this structure, the dashes (-) represent the covalent bonds formed between the phosphorus and fluorine atoms, each dash representing a shared electron pair. There are 3 single covalent bonds in PF₃, with a total of 6 electrons involved in the bonding (3 from phosphorus and 3 from the fluorine atoms).

Key Concepts

Understanding Valence Electrons

Valence electrons are the outermost electrons of an atom that are involved in forming chemical bonds. The number of valence electrons determines an atom's chemical properties and its ability to form bonds with other atoms. In the formation of phosphorus trifluoride ((PF_3), the valence electrons play a crucial role. Phosphorus has five valence electrons, while each fluorine atom has seven.

The Lewis symbols help us visualize these valence electrons as dots around the element's symbol. For example, the Lewis symbol for phosphorus (P) would be written with five dots around it representing its valence electrons. Similarly, for fluorine (F), we would draw seven dots around the symbol. The arrangement and pairing of these valence electrons through Lewis symbols become the foundation for predicting the bonding behavior of atoms in a molecule.

The Nature of Covalent Bonds

Covalent bonds form when atoms share pairs of valence electrons, creating a stable balance of attractive and repulsive forces between them. In our example of phosphorus trifluoride ((PF_3), each of the three fluorine atoms shares one of its valence electrons with phosphorus, resulting in the formation of single covalent bonds. These shared pairs of electrons, or bonding pairs, are represented as dashes in Lewis structures.

In (PF_3), there are three covalent bonds between the phosphorus and the fluorine atoms. Each bond consists of one electron from phosphorus and one from fluorine, contributing to a stable molecule. Covalent bonding is essential to molecular chemistry and dictates the structure and shape of a molecule, influencing both its physical and chemical properties.

The Octet Rule in Molecule Formation

The octet rule is a chemical rule of thumb which states that atoms tend to form molecules in a way that each atom has eight electrons in its valence shell, giving it the same electron configuration as a noble gas. The formation of phosphorus trifluoride ((PF_3) perfectly illustrates the octet rule. Each fluorine atom aims to complete its valence shell with eight electrons, and by sharing an electron with phosphorus through covalent bonding, every fluorine achieves this stable configuration.

Phosphorus, on the other hand, starts with five valence electrons and acquires three more from the fluorine atoms through bonding, reaching an octet. In the Lewis structure of (PF_3), this is evident as each atom is surrounded by eight electrons, satisfying the octet rule. This concept is fundamental in understanding the stability of most molecules, as following the octet rule generally leads to chemically stable configurations.