Question

Draw the electron-dot formula for each of the following covalent molecules: a. \(\mathrm{NI}_{3}\) b. \(\mathrm{CCl}_{4}\) c. \(\mathrm{Cl}_{2}\) d. \(\mathrm{SiF}_{4}\)

Short answer

NI3: I:N:I with lone pairs on I; CCl4: Cl:C:Cl with lone pairs on Cl; Cl2: Cl - Cl with lone pairs on Cl; SiF4: F:Si:F with lone pairs on F.

Step-by-step solution

Determine the Total Number of Valence Electrons

Count the total number of valence electrons for each molecule by summing the valence electrons of all the atoms present. For instance, in \( \mathrm{NI}_{3} \), nitrogen has 5 valence electrons and each iodine has 7.

Draw the Basic Skeleton Structure

Arrange the atoms to reflect the molecular structure, generally starting with the least electronegative atom (other than hydrogen) in the center. Connect the atoms with single bonds (pairs of shared electrons).

Distribute Remaining Electrons to Complete the Octets

Place the remaining electrons around the atoms to satisfy the octet rule (8 electrons around each atom), starting with the outer atoms first and then moving to the central atom.

Adjust for Multiple Bonds if Necessary

If there are leftover electrons or if the central atom lacks an octet, move lone pairs from outer atoms to form double or triple bonds as needed.

Draw Electron-Dot Formulas for Each Molecule

For \( \mathrm{NI}_{3} \):- Total valence electrons = 5 (N) + 3 × 7 (I) = 26- Skeleton structure: I - N - I- Add lone pairs to iodine atoms: \( \mathrm{I:N:I} \) with lone pairs on each I.For \( \mathrm{CCl}_{4} \):- Total valence electrons = 4 (C) + 4 × 7 (Cl) = 32- Skeleton structure: C in the center with 4 Cl atoms single-bonded: \( \mathrm{Cl:C:Cl} \) with lone pairs on each Cl.For \( \mathrm{Cl}_{2} \):- Total valence electrons = 2 × 7 (Cl) = 14- Skeleton structure: Cl - Cl with 3 lone pairs on each Cl.For \( \mathrm{SiF}_{4} \):- Total valence electrons = 4 (Si) + 4 × 7 (F) = 32- Skeleton structure: Si in the center with 4 F atoms single-bonded: \( \mathrm{F:Si:F} \) with lone pairs on each F.

Key concepts

Valence Electrons

Valence electrons are the outermost electrons of an atom.
These electrons are crucial because they participate in forming chemical bonds.
When drawing electron-dot formulas, it's important to know how many valence electrons each atom has.
For example:

• Nitrogen (N) has 5 valence electrons.
• Iodine (I) has 7 valence electrons.
• Carbon (C) has 4 valence electrons.
• Chlorine (Cl) has 7 valence electrons.
• Silicon (Si) has 4 valence electrons.
• Fluorine (F) has 7 valence electrons.

Knowing this helps us accurately draw the electron-dot structures and ensure each atom achieves a stable configuration.

Covalent Bonds

Covalent bonds are formed when atoms share pairs of electrons.
In electron-dot formulas, these bonds are represented by lines between atoms.
Each line corresponds to a pair of shared electrons.
For example, in the case of \( \mathrm{CCl}_{4} \):

• Carbon shares four pairs of electrons with four chlorine atoms.

This sharing of electrons allows each atom to effectively fill their outer electron shells, achieving greater stability.
Understanding covalent bonds is key to drawing accurate molecular structures in electron-dot formulas.

Octet Rule

The octet rule states that atoms tend to form bonds until they have eight electrons in their outer shell.
This rule is a guideline that helps predict how atoms will bond and arrange themselves.
For example, in the molecule \( \mathrm{NI}_{3} \):

• Nitrogen shares three pairs of electrons with three iodine atoms.
• Each iodine completes its octet with three lone pairs of electrons.

However, there are exceptions to the octet rule. Some atoms can have fewer or more than eight electrons in their valence shell.
Exceptions include molecules like \( \mathrm{BF}_{3} \) and \( \mathrm{SF}_{6} \).
Overall, the octet rule helps simplify the process of drawing electron-dot structures.

Molecular Structure

The molecular structure refers to the arrangement of atoms within a molecule.
Understanding the molecular structure helps in predicting the chemical behavior of the molecule.
When drawing electron-dot formulas, start with a basic skeleton where the central atom is often the least electronegative (except hydrogen).
For example, in the molecule \( \mathrm{SiF}_{4} \):

• Silicon is the central atom, surrounded by four fluorine atoms.

Once the basic structure is formed, adjust electrons to meet the octet rule and form stable molecules.
Remember that drawing an accurate molecular structure is essential for understanding the interactions between atoms and the resulting properties of the molecule.