Problem 5 - Introductory Chemistry Atoms First

Question

What is the molecular formula of the compound that forms between \(\mathrm{H}\) atoms and \(\mathrm{F}\) atoms? Justify your answer with dot diagrams.

Step-by-Step Solution

Answer

The molecular formula of the compound that forms between hydrogen (H) and fluorine (F) atoms is \(\mathrm{HF}\). This is justified by using dot diagrams to represent the valence electrons of each atom. Both elements need one more electron to achieve their respective stable electron configurations. They form a covalent bond by sharing an electron pair, resulting in the formation of the \(\mathrm{HF}\) molecule.

Step 1: Identify Valence Electrons for Each Element.

To determine the molecular formula, we first need to know how many valence electrons are present in each element. Hydrogen belongs to Group 1 and has 1 valence electron, while fluorine belongs to Group 7 and has 7 valence electrons.

Step 2: Draw Dot Diagrams for Each Element.

Now we will draw dot diagrams for hydrogen and fluorine. The dot diagram represents the element's symbol surrounded by dots representing its valence electrons. For hydrogen: H • For fluorine: • • F • •

Step 3: Observe Possible Bonds.

In order to achieve a stable electron configuration (a full valence shell), hydrogen needs one more electron to achieve a full 1s orbital (2 electrons), while fluorine needs one more electron to achieve a full 2p orbital (8 electrons in total for the 2s and 2p orbitals). Both hydrogen and fluorine will share an electron pair to achieve their respective stable configurations. This sharing of an electron pair forms a covalent bond between hydrogen and fluorine.

Step 4: Draw the Bonded Dot Diagram.

Now we will draw the bonded dot diagram, with the shared electron pair represented between the two elements, forming a covalent bond. H • | • F •

Step 5: Determine Molecular Formula.

Since one hydrogen atom forms a bond with one fluorine atom (sharing an electron pair), the molecular formula for the compound that forms between hydrogen and fluorine is \(\mathrm{HF}\). So, the molecular formula of the compound is \(\mathrm{HF}\).

Key Concepts

Valence Electrons

Atoms are composed of protons, neutrons, and electrons. The electrons occupy regions around the nucleus known as electron shells. The outermost shell of an atom contains electrons called valence electrons. These are crucial in determining how atoms interact and bond with each other.

• Valence electrons dictate the chemical properties of an element.
• They are responsible for the formation of chemical bonds.
• In general, elements strive to have a full set of valence electrons to achieve stability.

In the case of hydrogen (H) and fluorine (F), each element uses its valence electrons to create bonds. Hydrogen, found in Group 1 of the periodic table, has one valence electron. Fluorine, located in Group 7, possesses seven valence electrons. The differences in these electron counts lead to unique bonding capabilities and drive the formation of molecules like HF.

Dot Diagrams

Dot diagrams, also known as Lewis dot structures, are a simple way to represent valence electrons around an atom. In this form of notation, each element is symbolized by its chemical symbol, surrounded by dots that represent its valence electrons.

• These diagrams help visualize how atoms bond in molecules.
• They illustrate how atoms share or exchange electrons to achieve stability.
• Dot diagrams simplify the process of predicting molecular bonding patterns.

To visualize hydrogen and fluorine bonding, consider their dot diagrams: - Hydrogen's diagram is shown as \( \text{H} \cdot \) - Fluorine's is depicted as \( \cdot\cdot\text{F}\cdot\cdot \)

These diagrams make it clear that hydrogen needs one more electron to complete its 1s orbital, while fluorine requires one more to fill its valence shell to eight electrons. By sharing their electrons, they form a bond necessary for their electron stability.

Molecular Formula

A molecular formula expresses the number and type of atoms in a molecule. It is derived from understanding how atoms bond to form a stable structure. In the case of a compound like HF:

• The molecular formula represents actual numbers of atoms in each molecule.
• It includes the empirical nature in which atoms are bonded.

For HF, we consider each hydrogen atom bonding with a fluorine atom. The chemical representation derived from these interactions is simple yet immensely informative.

The formation of HF involves one hydrogen atom sharing its lone electron with one fluorine atom, completing both of their valence electron needs. Consequently, the molecular formula is straightforward as \( \mathrm{HF} \), illustrating a one-to-one ratio of hydrogen and fluorine within the molecule, highlighting the simplicity and elegance of covalent bonding.

Stable Electron Configuration

Atoms tend to bond in ways that result in a stable electron configuration. This stability usually aligns with achieving a full outer electron shell, akin to the noble gases in the periodic table.

• Stable electron configurations are often referred to as "octet rules" which elements tend to follow.
• In bonding, atoms share, donate, or receive electrons to reach such configurations.

For hydrogen, stability is achieved with just two electrons filling its 1s orbital, known as a "duet." For elements like fluorine, a full set of eight electrons in its outer shell results in maximum stability.

When hydrogen bonds with fluorine to form HF: - Hydrogen shares its one electron, gaining stability with two electrons. - Fluorine benefits from hydrogen's electron, achieving the coveted octet in its valence shell.

Understanding stable electron configurations is essential to grasp why certain molecular formulas, like HF, form and persist in nature's vast tapestry of chemical reactions.