Question

Write the Lewis structure for each molecule. a. \(\mathrm{CH}_{2} \mathrm{O}\) b. \(\mathrm{C}_{2} \mathrm{Cl}_{4}\) c. \(\mathrm{CH}_{3} \mathrm{NH}_{2}\) d. CFCl \(_{3}\) (C central)

Short answer

a. H2C=O, b. Cl2C-CCl2, c. H3C-NH2 with one lone pair on N, d. F-C(Cl)3 with three lone pairs on each Cl and one lone pair on F.

Step-by-step solution

Determine the valence electrons for each atom in CH2O

Carbon (C) has 4 valence electrons, Hydrogen (H) has 1 (total of 2 for two H), and Oxygen (O) has 6. Total valence electrons = 4 + 2(1) + 6 = 12.

Draw the skeletal structure for CH2O

Put Carbon in the center with Oxygen double bonded to it and Hydrogen atoms single bonded to Carbon.

Complete the octets for CH2O

Carbon and Oxygen will share electrons to complete their octet, while Hydrogens already have completed their duet.

Determine the valence electrons for each atom in C2Cl4

Each Carbon (C) has 4 valence electrons (total of 8 for two C), and each Chlorine (Cl) has 7 (total of 28 for four Cl). Total valence electrons = 8 + 28 = 36.

Draw the skeletal structure for C2Cl4

Put the two Carbons in the center bonded to each other with Chlorines single bonded to each of the Carbons.

Complete the octets for C2Cl4

Each Chlorine will have three lone pairs and the Carbons will share electrons to complete their octet.

Determine the valence electrons for each atom in CH3NH2

Carbon (C) has 4 valence electrons, each Hydrogen (H) has 1 (total of 3 for three H), and Nitrogen (N) has 5. Total valence electrons = 4 + 3(1) + 5 = 12.

Draw the skeletal structure for CH3NH2

Put Carbon in the center with three Hydrogen atoms single bonded to it and Nitrogen single bonded to Carbon with Hydrogen single bonded to Nitrogen.

Complete the octets for CH3NH2

Nitrogen will have one lone pair, Carbon will be bonded to Hydrogens and Nitrogen, each Hydrogen will have a complete duet.

Determine the valence electrons for each atom in CFCl3

Carbon (C) has 4 valence electrons, Fluorine (F) has 7, and each Chlorine (Cl) has 7 (total of 21 for three Cl). Total valence electrons = 4 + 7 + 21 = 32.

Draw the skeletal structure for CFCl3

Place the Carbon in the center with Fluorine single bonded to it and the three Chlorine atoms single bonded to the Carbon.

Complete the octets for CFCl3

Fluorine and the Chlorines will have three lone pairs each, filling their octets, while Carbon will share electrons with each of them.

Key concepts

Valence Electrons

Valence electrons are the electrons located in the outermost shell of an atom, and they play a crucial role in chemical bonding. For instance, Carbon (C) has four valence electrons, Hydrogen (H) has one, Oxygen (O) has six, and Chlorine (Cl) has seven. The number of valence electrons helps in determining how an atom will bond with others. In constructing a Lewis structure, we tally these electrons to understand an atom's potential for forming bonds.

It's important to remember that the noble gases, sitting at each end of the periodic table, have a full valence shell and typically do not participate in bonding without special conditions. Learning the number of valence electrons in each element is a foundational step in predicting molecular structures and their properties. For homework exercises such as these, counting valence electrons sets the stage for the rest of the problem-solving process.

Octet Rule

The octet rule is a principle based on the observation that atoms tend to bond in such a way that they have eight electrons in their valence shell, resembling the electron configuration of a noble gas. The only exception is Hydrogen, which follows the 'duet rule', preferring to have just two electrons. In the provided exercise, we observe this rule when completing the octets for different molecules.

For example, in CH2O, Carbon and Oxygen share electrons so that each ends up with eight electrons in its valence shell. The octet rule guides us in placing single or double bonds and in allocating lone pairs in Lewis structures. However, there are exceptions to this rule, which usually involve elements in the third row of the periodic table and beyond, as they can have more than eight valence electrons due to their ability to utilize d-orbitals.

Chemical Bonding

Chemical bonding is the process by which atoms combine to form compounds. At the heart of this process is the idea that atoms bond in ways that minimize their potential energy, usually by achieving a stable valence electron configuration. Bonds can be ionic or covalent: Ionic bonds result from the attraction between oppositely charged ions, while covalent bonds involve the sharing of electron pairs between atoms.

In the Lewis structures for molecules like CH2O, C2Cl4, CH3NH2, and CFCl3, we focus on covalent bonding as electrons are shared between nonmetal atoms to fulfill the octet rule. The step-by-step solutions for these structures demonstrate how to determine the number of valence electrons, create the skeletal arrangement of atoms, and then complete the octets or duets, thus finalizing the Lewis structures. Correctly predicting chemical bonding patterns is crucial for understanding molecular geometry, polarity, and reactivity.