Question

Draw an acceptable Lewis electron dot diagram for these molecules that violate the octet rule. a) POF3 b) ClF3

Short answer

POF3 has 32 and ClF3 has 28 valence electrons, both have central atoms with expanded octets.

Step-by-step solution

Count the valence electrons for POF3

Phosphorus is in group 15 and has 5 valence electrons. Oxygen is in group 16 and has 6 valence electrons. Fluorine, in group 17, has 7 valence electrons. The total number of valence electrons for one POF\(_3\) molecule is: \(1 \times 5 + 1 \times 6 + 3 \times 7 = 32\) electrons.

Draw the Lewis structure for POF3

Place the phosphorus atom in the center. Connect it to one oxygen atom and three fluorine atoms using single bonds. The P-F bonds and the P=O double bond will satisfy the molecule's valence electron requirements. Finalize the structure by distributing the remaining electrons to satisfy the octet for F and O, while P can exceed the octet since it is in period 3. The final structure consists of a central P atom with one double bond to O and single bonds to each F.

Count the valence electrons for ClF3

Chlorine is in group 17 and has 7 valence electrons. Each fluorine atom has 7 valence electrons as well. The total number of valence electrons for ClF\(_3\) is: \(1 \times 7 + 3 \times 7 = 28\) electrons.

Draw the Lewis structure for ClF3

Place the chlorine atom in the center. Connect it with three fluorine atoms using single bonds. Arrange the remaining electrons to fill the octet for the fluorine atoms. Chlorine will have 10 electrons around it, which is acceptable since it can accommodate more than 8 electrons due to its position in period 3. The chlorine atom is surrounded by three single bonds to F atoms and two lone pairs.

Key concepts

Octet Rule

The octet rule is a fundamental principle in chemistry that helps us understand how atoms combine to form molecules. According to this rule, atoms tend to gain, lose, or share electrons in order to achieve a stable electron configuration, which usually amounts to eight electrons in their valence shell. This reflects the natural stability seen in noble gases, which inherently have complete valence shells.

However, there are important exceptions to the octet rule. Some elements, particularly those in period 3 and beyond, can hold more than eight electrons in their outer shell. This is because these elements have access to d orbitals, which can accommodate extra electrons.

When drawing Lewis structures for molecules like POF eighborhood {3} and ClF eighborhood {3} that violate the octet rule, it's crucial to remember this flexibility. Phosphorus in POF eighborhood {3} and chlorine in ClF eighborhood {3} can exceed an octet, allowing them to accommodate additional electrons and form stable compounds.

Valence Electrons

Valence electrons are the outermost electrons of an atom and are pivotal in determining how elements will bond with others. These electrons exist in the highest energy level and are responsible for the chemical properties of the element. When drawing Lewis structures, it's essential to count the total number of valence electrons for all atoms involved in a molecule.

For example, in the molecule POF eighborhood {3}, phosphorus has 5 valence electrons, oxygen has 6, and each fluorine has 7. After summing these values, we find a total of 32 valence electrons to distribute in the molecule.

In ClF eighborhood {3}, we perform a similar count. Chlorine contributes 7 valence electrons, while each of the three fluorine atoms also contributes 7, totaling 28 valence electrons for the entire molecule.
These numbers guide the arrangement of electrons in the molecule and help determine the structure that satisfies all bonding requirements. Utilizing valence electrons appropriately ensures each atom generally reaches a stable electronic arrangement.

Electron Dot Diagrams

Electron dot diagrams, commonly referred to as Lewis structures, are a visual representation of the valence electrons in an atom or molecule. These diagrams help predict the kind of bonds atoms can form, how these atoms are arranged within a molecule, and the eventual shape and electron configuration of the molecule.

In drawing a Lewis structure, one starts by calculating the total number of valence electrons available. Then, one places the central atom and connects other atoms using electron pairs as bonds, ensuring each bond is represented by two electrons (a pair).

For POF eighborhood {3}, phosphorus is placed in the center with oxygen and fluorine atoms surrounding it. A double bond connects the phosphorus to the oxygen, while each fluorine is connected via single bonds. This configuration accounts for each atom's distribution of valence electrons.
For ClF eighborhood {3}, the central chlorine atom forms single bonds with each fluorine atom, with the remaining electrons shown as lone pairs around the chlorine. Such diagrams are instrumental in visualizing how molecules with elements that can exceed the typical octet stabilize themselves.