Question

Write the electron dot formula and draw the structural formula for each of the following molecules. (The central atom is indicated in bold.) (a) \(\mathrm{H}_{2}\) (b) \(F_{2}\) (c) HBr (d) \(\mathbf{N H}_{3}\)

Short answer

Electron dot and structural formulas are drawn with valence electrons and bonds shown.

Step-by-step solution

Understand Electron Dot and Structural Formulas

We need to represent the valence electrons for each molecule using dots around the atomic symbols (electron dot formula) and show the connectivity and bonds in the molecule using lines (structural formula).

Solve for (a) \( \text{H}_2 \)

For \( \text{H}_2 \), each hydrogen atom has one valence electron. The electron dot formula is displayed as \( \text{H} : \text{H} \). The structural formula is represented by a single bond: \( \text{H} - \text{H} \).

Solve for (b) \( \text{F}_2 \)

Each fluorine atom has 7 valence electrons. In the electron dot formula, they share one pair of electrons to complete their octets, represented as \( \text{F} : \text{F} \) with each fluorine surrounded by three additional dots (pairs). The structural formula is \( \text{F} - \text{F} \).

Solve for (c) \( \text{HBr} \)

Hydrogen has 1 valence electron, and bromine has 7. The electron dot formula is \( \text{H} : \text{Br} \) with three pairs of dots around bromine. The structural formula is \( \text{H} - \text{Br} \).

Solve for (d) \( \text{\bf{NH}_3} \)

Nitrogen has 5 valence electrons and needs three more to complete its octet, which it gets by forming bonds with three hydrogens. The electron dot formula shows nitrogen with a lone pair and three pairs of shared electrons: \( \text{H}:\text{N}:\text{H} \), with a lone pair of electrons on nitrogen. The structural formula is \( \text{H} - \text{N} \) (with a lone pair) - \( \text{H} \), arranged in a trigonal pyramidal shape.

Key concepts

Valence Electrons

Valence electrons are the outermost electrons of an atom, residing in the outer shell of an electron cloud. These electrons play a crucial role in chemical bonding, as they are the ones involved in forming bonds with other atoms. When two atoms approach each other, they can share or transfer valence electrons, creating stable associations such as molecules or ionic compounds. Recognizing the number of valence electrons can help predict an element's reactivity and the types of chemical bonds it is likely to form.

For instance, in hydrogen ( H_2 ), each hydrogen atom has one valence electron. These electrons pair up to form a single bond, giving each atom the full complement of two electrons, which they need to achieve the electron configuration of helium. Similarly, fluorine ( F_2 ) atoms each possess seven valence electrons. They share a single pair to complete each other's octet, leading to the formation of a diatomic molecule with a shared electron pair.

Understanding valence electrons is vital in determining how atoms interact with one another, and it serves as a guide for drawing both electron dot formulas and structural formulas.

Structural Formula

A structural formula provides a visual representation of how atoms are bonded in a molecule. It uses lines to show the bonds between atoms, providing a clearer understanding of the molecule's shape and layout. Each line represents a bond, a pair of shared electrons between atoms.

In the structural formula of H_2 , a single line between the two H atoms ( H-H ) indicates a single bond formed by their shared electrons. Similarly, the F_2 molecule is represented as F-F , showcasing the single bond formed by the shared electron pair. For NH_3 , the structural formula H-N-H - H illustrates the bonds connecting nitrogen to three hydrogen atoms. Nitrogen also has a lone pair of electrons, a concept that can be shown but is often omitted in simple structural formulas for clarity.

The structural formula is a fundamental tool for chemists to visualize molecular connectivity and identify how atoms are arranged spatially in relation to one another. This representation not only helps in understanding chemical structures but also in predicting molecular interactions and reactions.

Electron Dot Formula

The electron dot formula, also known as the Lewis dot structure, represents the valence electrons of atoms within a molecule. It visually demonstrates how electrons are shared between atoms or remain as lone pairs. This form of notation is particularly helpful for understanding how atoms achieve stable electronic configurations through bonding.

The electron dot formula for H_2 illustrates a pair of electrons shared between H atoms: H : H. For F_2 , the electron dot formula appears as F : F, with each F atom surrounded by three lone pairs to fulfill the octet rule. When examining HBr, the electron dot formula H : Br shows the shared pair between hydrogen and bromine, with bromine also bearing three pairs of lone electrons around it.

For a molecule like NH_3, the electron dot formula demonstrates nitrogen bonding with three hydrogen atoms, while still retaining one lone pair of electrons on nitrogen. Such visualizations are instrumental in grasping how atoms within a molecule share or retain electrons, ensuring students can understand molecular geometries and potential chemical behavior.