Problem 85 - Chemistry

Question

Draw structures for (a) (HF) \(_{2}\), (b) \(\mathrm{HF}_{2}^{-}\).

Step-by-Step Solution

Answer

Lewis structures are used to represent the distribution of electrons in a molecule. For (HF) \(_{2}\), each HF forms a single bond by sharing a pair of electrons. For \(\mathrm{HF}_{2}^{-}\), H forms a single bond with each F.

Step 1: Draw Lewis structure for (HF) \(_{2}\)

Determine the total number of valence electrons. Hydrogen (H) has 1 and Fluorine (F) has 7 valence electrons. Since there are two (HF), the total is 2*(1+7) = 16 valence electrons. Chemical bond formation involves sharing of electrons, usually a pair, between atoms. So, connect each H and F with a single bond (pair of electrons) and complete octet around Fluorine using remaining electrons.

Step 2: Draw Lewis structure for \(\mathrm{HF}_{2}^{-}\)

Determine the total number of valence electrons. Hydrogen (H) has 1 and Fluorine (F) has 7 valence electrons. Since there are two fluorine atoms and one extra electron due to negative charge, the total is 1+2*7+1=16 valence electrons. Connect H and each F with a single bond (pair of electrons) and complete the octet around F using remaining electrons.

Key Concepts

Chemical Bonding

When it comes to understanding molecules, chemical bonding is a fundamental concept that explains how atoms stick together to form various compounds. At its heart lies the desire of atoms to reach a stable configuration, which they achieve by either sharing, gaining, or losing electrons. With Lewis structures, we visually represent these bonds, showing how atoms fulfill their company. For example, in a molecule like hydrogen fluoride (HF), a bond forms when hydrogen shares its lone electron with fluorine, allowing both to edge closer to stability.

In more complex molecules or ions such as \(\mathrm{HF}_{2}^{-}\), the bonding reveals a unique relationship. Hydrogen still shares its electron, but this time with two fluorine atoms, forming what are known as '3-center 4-electron' bonds. The Lewis structures for such species require careful electron counting to ensure that each bond is appropriately represented and the overall charge on the ion is accurate. Chemical bonds are, indeed, the glue that holds the molecular world together, and mastering the depiction of these bonds through Lewis structures is a skill that provides a deeper insight into the nature of chemical compounds.

Valence Electrons

Understanding valence electrons is like holding the key to a treasure chest of chemical behavior. These are the electrons found in the outermost shell of an atom and are responsible for the chemical bond formation. Valence electrons can be envisioned as the hands of an atom, reaching out to hold onto other atoms and create a stable structure.

For instance, hydrogen has one valence electron and fluorine has seven. With this information, we can predict how they might bond in the molecule HF or the ion \(\mathrm{HF}_{2}^{-}\). The HF molecule shares one pair of electrons, while the ion \(\mathrm{HF}_{2}^{-}\) must account for an extra electron due to its negative charge, resulting in different bonding and structural arrangement. When drawing Lewis structures, correctly counting these valence electrons becomes critical as they determine how atoms are connected and the overall stability of the molecule or ion.

Octet Rule

The octave rule is akin to a rule of thumb in chemistry emphasizing that atoms tend to be more stable when they have eight electrons in their valence shell—resembling the electron configuration of noble gases. For many elements, this means sharing or trading electrons to reach this coveted arrangement.

Take, for example, the molecules and ions such as HF and \(\mathrm{HF}_{2}^{-}\). In both cases, the fluorine atom aims for an octet. Since hydrogen has just the one electron to share, fluorine gladly accepts it, achieving a full octet which epitomizes its desired stability in HF. Amidst complication in \(\mathrm{HF}_{2}^{-}\), each fluorine still grasps for a complete octet which, now with the addition of an extra electron in the system, they successfully attain. The octet rule serves as a guide in constructing Lewis structures because it lets us know how to distribute electrons until each atom, apart from hydrogen, is either surrounded by eight electrons or has formed enough bonds to be surrounded by eight valence electrons.