Question

The only known argon-containing compound is HArF, which was prepared in \(2000 .\) Draw a Lewis structure of the compound.

Short answer

The Lewis structure for HArF would have Argon in the center, connected to Hydrogen and Fluorine through single bonds, with two lone pairs of electrons on Argon and three on Fluorine.

Step-by-step solution

Count the Number of Valence Electrons

Argon (Ar) has 8 valence electrons being a noble gas, Hydrogen (H) has 1 electron and Fluorine (F) has 7 electrons. Add all the valence electrons to find the total valence electrons of the molecule, which is \(8 + 1 + 7 = 16\) electrons.

Atom Arrangement

Argon being the least electronegative (except for Hydrogen) is placed at the center of the structure. Hydrogen can only form one bond, thus is always placed on the exterior. The structure would thus look like this H-Ar-F.

Distribute Electrons into the Diagram

Introduce single bonds between H-Ar and Ar-F. After this, each bond will account for 2 of the 16 valence electrons, remaining with 12 electrons. Fill in the remaining electrons pair to complete octets. Argon and Fluorine each need 8, however, we subtract the 2 electrons from the bond which means we need to allocate another 12 electrons (6 electron pairs)

Key concepts

Valence Electrons

Valence electrons are the electrons that reside in the outermost shell of an atom, playing a crucial role in chemical bonding and the formation of molecules. In the case of HArF, a unique compound consisting of Hydrogen (H), Argon (Ar), and Fluorine (F), we must calculate the total number of these electrons to predict its chemical structure.

Argon, a noble gas, has 8 valence electrons in its natural state. This full outer shell typically makes noble gases chemically inert, but in certain conditions and in the presence of highly reactive elements, they can form compounds. Hydrogen, on the other hand, possesses 1 valence electron and is always looking to either gain an extra electron or share one to achieve a more stable configuration. Fluorine, with 7 valence electrons, is known for its strong electronegativity and tendency to attract electrons to fill its outer shell to achieve stability.

When we sum up the valence electrons for HArF, we count 8 from Argon, 7 from Fluorine, and 1 from Hydrogen, reaching a total of 16 valence electrons which are available to form bonds and lone pairs in the molecule.

Electron Dot Diagram

The electron dot diagram, often referred to as Lewis structure, is a schematic representation that illustrates the positioning of valence electrons around atoms within a molecule. For our subject molecule HArF, the diagram begins with determining the central atom, which in this case, by convention, is Argon (Ar) as it is the least electronegative element (except for Hydrogen).

With the arrangement H-Ar-F, we form single bonds between Hydrogen-Ar and Ar-Fluorine. Each bond represents a pair of shared electrons and accounts for 2 of the 16 total valence electrons. Following the creation of bonds, we distribute the remaining electrons to satisfy the octet rule where possible. The octet rule states that atoms tend to form structures where they have eight electrons in their valence shell. After placing single bonds, we allocate the rest of the electrons as lone pairs to fill the octets of Argon and Fluorine, ensuring that all 16 valence electrons are accounted for in the structure.

Molecular Geometry

Molecular geometry refers to the three-dimensional arrangement of atoms within a molecule. The geometry influences the molecule's physical and chemical properties, such as polarity, reactivity, and color. In the case of HArF, the molecular geometry is significantly impacted by the distribution of the valence electrons after they have been placed in bonds and as lone pairs.

Argon's rare participation in compounds adds a layer of complexity to predicting the geometry of HArF. Generally, the VSEPR (Valence Shell Electron Pair Repulsion) theory is used to determine the shape of a molecule. According to this theory, electron pairs around a central atom will arrange themselves as far apart from each other as possible to minimize repulsion. With one bond to Hydrogen and one to Fluorine, and with lone pairs positioned on the Argon, HArF is expected to display a linear geometry for the H-Ar-F atoms since there are no lone pairs on the Argon to repel the bonded atoms into a bent shape. This simplistic prediction assumes that the presence of Argon doesn't introduce significant distortions, which in practice, may not be entirely accurate due to Argon's unique chemistry.