Question

Write the electron dot formula and draw the structural formula for each of the following molecules: (a) \(\mathrm{CCl}_{4}\) (b) \(\mathrm{HONO}_{2}\) (c) \(\mathrm{CH}_{3} \mathrm{OH}\) (d) HOCN

Short answer

Electron dot structures detail electron allocation; structural formulas simplify bonds to lines.

Step-by-step solution

Determine Valence Electrons

To start, figure out the total number of valence electrons for each molecule. - **(a) \( \mathrm{CCl}_{4} \):** Carbon (C) has 4 valence electrons and each Chlorine (Cl) has 7, so total is \(4 + 4\times7 = 32\).- **(b) \( \mathrm{HONO}_{2} \):** Hydrogen (H) has 1, Oxygen (O) has 6, and Nitrogen (N) has 5. Total is \(1 + 5 + 2\times6 + 5 = 24\).- **(c) \( \mathrm{CH}_{3} \mathrm{OH}\):** Carbon (C) 4, Hydrogen (H) 1 (for each of the 4 H), and Oxygen (O) 6, so total is \(4 + 4\times1 + 6 = 14\).- **(d) \( \mathrm{HOCN} \):** Hydrogen (H) 1, Oxygen (O) 6, Carbon (C) 4, and Nitrogen (N) 5, so total is \(1 + 6 + 4 + 5 = 16\).

Draw Basic Atomic Skeleton

Arrange the atoms to reflect their likely connectivity, using symmetries in molecular formulas as a guide.- **(a)\( \mathrm{CCl}_{4} \):** C is central, surrounded by 4 Cl atoms.- **(b) \( \mathrm{HONO}_{2} \):** Connect H to O, which bonds to N. Each N is bonded to two O atoms.- **(c) \( \mathrm{CH}_{3} \mathrm{OH} \):** C is central, bonded to three H atoms and the remaining O. Connect the O to another H.- **(d) \( \mathrm{HOCN} \):** Connect H to O, then to C, then to N.

Allocate Valence Electrons

Distribute the valence electrons around the atoms, starting with single bonds between directly connected atoms in the basic skeleton.- **(a) \( \mathrm{CCl}_{4} \):** Place 8 electrons around each Cl. All Cls share 1 electron with C, totaling each bond as a pair (single bond).- **(b) \( \mathrm{HONO}_{2} \):** Create N-O single bonds, with one O having a double bond to N. The remaining valence electrons fulfill octets where needed.- **(c) \( \mathrm{CH}_{3} \mathrm{OH} \):** Allocate single bonds between C and four attachments (3 H, 1 O), then bond O to H.- **(d) \( \mathrm{HOCN} \):** Make H-O, O-C, and C-N connections, using remaining valence to complete multiple bonds between elements as necessary.

Drawing the Structural Formulas

Convert the electron dot representation to a simple line structure. Each line indicates a pair of shared electrons.- **(a) \( \mathrm{CCl}_{4} \):** The structure shows C at the center with 4 lines going out to each Cl atom.- **(b) \( \mathrm{HONO}_{2} \):** H-O-N(=O)-O. One O is double-bonded to the N, illustrating the stabilization of the octet rule.- **(c) \( \mathrm{CH}_{3} \mathrm{OH} \):** Structural formula: H-C-H (two more H bonded to the central C) and C-O-H for the alcohol group.- **(d) \( \mathrm{HOCN} \):** Structure: H-O-C≡N, indicating the triple bond between carbon and nitrogen.

Verify Octet and Duplet (H) Rules

Ensure that the electron arrangement on each atom satisfies the octet rule for main group elements and the duplet rule for hydrogen. - All structures should complete 8-electron configurations around carbon, nitrogen, and oxygen. Hydrogen should only engage in single bonds (2 electrons or a duplet).

Key concepts

Valence Electrons

Valence electrons are the electrons in the outermost shell of an atom. These electrons are significant as they are involved in forming chemical bonds. Understanding how to count and use valence electrons is fundamental when drawing electron dot formulas and predicting molecular structures.

Identifying valence electrons involves looking at an element's position on the periodic table. For example, carbon has 4 valence electrons, while each chlorine atom in CCl_4 has 7. In HONO_2, you have to tally valence electrons from hydrogen (1), oxygen (6 per oxygen), and nitrogen (5). The total number of valence electrons determines how atoms connect and bond with one another.

• Electron sharing can form covalent bonds, involving a pair of shared electrons, which are part of the electron dot formula.
• For HOCN, you are counting valence electrons from 1 hydrogen, 4 from carbon, 6 from oxygen, and 5 from nitrogen, totaling 16 electrons.

Molecular Structures

Molecular structures offer a visual representation of how atoms bond together in a molecule.
To create a molecular structure, start with the basic atomic skeleton based on likely connectivity.
For example, in CCl_4, carbon is centrally bonded to four chlorine atoms, forming a symmetrical tetrahedral shape. This structure arises from carbon's four valence electrons bonding with chlorine's seven valence electrons.

In CH_3OH, we arrange the atoms with carbon bonding to three hydrogens and one oxygen, and the oxygen further bonding to another hydrogen.

Drawing these structures helps visualize the molecule's shape and can predict chemical behavior.

Octet Rule

The octet rule states that atoms tend to form bonds until they have eight electrons in their outer shell, similar to noble gases. This rule is crucial for understanding molecular stability and predicting how atoms bond.
In the case of HONO_2, nitrogen is bonded to one oxygen through a single bond and another oxygen through a double bond, based on the need to fulfill the octet rule. Each oxygen effectively acquires eight electrons in its outermost shell, either through sharing or gaining electrons, implying a stable arrangement.
Applying this rule is essential when distributing electron pairs in drawing molecular structures to ensure each main group element is stable. Hydrogen is the exception, following the duplet rule instead, seeking to pair its single electron with another atom's electron to form a stable di-electron configuration.

Chemical Bonds

Chemical bonds are the forces that hold atoms together in a molecule, and they involve the sharing of valence electrons.

There are different types of bonds, with the most common being covalent bonds, where atoms share electrons to achieve stable electron configurations.
In the molecule HOCN, various types of chemical bonds appear: a single bond between hydrogen and oxygen, a single bond between oxygen and carbon, and a strong triple bond between carbon and nitrogen. The triple bond is particularly notable for creating a strong connection, with six shared electrons establishing a stable arrangement.

• Single bonds are represented in line structures by one line, each symbolizing a shared electron pair.
• Double bonds have two lines, denoting two shared pairs of electrons, strengthening molecular connections.
• Triple bonds, like in HOCN between carbon and nitrogen, appear as three lines and represent an especially sturdy connection.