Question

Write a Lewis formula for each of the following: (a) \(\mathrm{NH}_{2} \mathrm{OH}\) (c) \(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{Cl}\) (e) \(\mathrm{HOCl}\) (b) \(\mathrm{CCl}_{4}\) (d) \(\mathrm{C}_{2} \mathrm{Br}_{2}\)

Short answer

Lewis structures for: \n (a) \(\mathrm{NH}_{2} \mathrm{OH}\): Nitrogen bonded with two Hydrogens and one Oxygen, which is further bonded with one hydrogen \n (b) \(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{Cl}\): Two central carbon atoms bonded to one Hydrogen and two more each, and one of them bonded with one Chlorine. \n (c) \(\mathrm{HOCl}\): Oxygen is central atom; bonded with one hydrogen and one Chlorine. \n (d) \(\mathrm{CCl}_{4}\): Carbon atom in the center, bonded with four Chlorine atoms. \n (e) \(\mathrm{C}_{2} \mathrm{Br}_{2}\): Two central carbon atoms, each bonded with one Bromine.

Step-by-step solution

Lewis Structure of \(\mathrm{NH}_{2} \mathrm{OH}\)

There are 14 valence electrons from atoms. The central atom is nitrogen, which is less electronegative than oxygen. Connect each hydrogen atom to nitrogen, and then connect oxygen to nitrogen. Add remaining electrons to all atoms complete their octets.

Lewis Structure of \(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{Cl}\)

There are 18 valence electrons from atoms. The central atoms are carbon as they are less electronegative than chlorine. Connect functionally important atoms (H to C and Cl to C). Distribute remaining valence electrons, aiming to fill the octets for all atoms.

Lewis Structure of \(\mathrm{HOCl}\)

There are 18 valence electrons from atoms. The central atom for this molecule is oxygen, which is less electronegative than Chlorine. Draw lines to connect O-H and O-Cl. Distribute remaining valence electrons, filling the octets around chlorine and oxygen.

Lewis Structure of \(\mathrm{CCl}_{4}\)

There are 32 valence electrons from atoms. The central atom is the carbon. Draw lines to connect carbon with four chlorine atoms. Distribute remaining valence electrons, filling the octets around each chlorine atom.

Lewis Structure of \(\mathrm{C}_{2} \mathrm{Br}_{2}\)

There are 24 valence electrons from atoms. The central atoms are the two carbon atoms. Draw lines to connect carbons together and to Bromine. Distribute remaining valence electrons, completing the octets around the carbon and bromine atoms.

Key concepts

Valence Electrons

Valence electrons are the outermost electrons of an atom and play a crucial role in chemical bonding. They are the electrons involved in forming bonds between atoms. To determine the number of valence electrons in an atom, locate its group number in the periodic table. For example, nitrogen, as used in \(\text{NH}_{2}\text{OH}\), is in group 15 and therefore has five valence electrons.

Understanding valence electrons allows us to predict how atoms will interact with each other. In Lewis structures, each "dot" represents a valence electron; these structures help visualize the bonding between atoms.

To find the total number of valence electrons for a molecule, sum up the valence electrons from each atom. For example, in the molecule \(\text{CCl}_4\), each carbon atom contributes four electrons, and each chlorine atom provides seven valence electrons, totaling 32 valence electrons.

Electronegativity

Electronegativity is an atom's tendency to attract and bond with electrons. It is a crucial concept in determining which atom becomes central in a molecule and how electrons are distributed in bonds. Typically, atoms with lower electronegativity values, like carbon and nitrogen, are centrally placed in molecules.

For instance, in the molecule \(\text{C}_2\text{Br}_2\), carbon is chosen as the central atom due to its lower electronegativity compared to bromine. When drawing Lewis structures, knowing the trend in electronegativity helps ensure the correct placement of atoms.

This concept also aids in predicting molecular properties such as bond polarity. Differences in electronegativity between two bonded atoms result in polar bonds, which are significant in determining molecular behavior and interactions.

Octet Rule

The octet rule is a principle stating that atoms tend to bond in ways that satisfy an outer shell configuration of eight electrons, akin to a noble gas. This rule helps explain the formation of stable molecules in chemical reactions.

For example, in \(\text{HOCl}\), the octet rule guides how electrons are distributed, ensuring that the oxygen and chlorine atoms each complete their outer shell with eight electrons. This distribution is shown in Lewis structures, where complete octets around the atoms often indicate stability.

However, it's essential to note that there are exceptions to the octet rule. Elements like hydrogen are satisfied with two electrons, and other elements like phosphorus or sulfur might expand their octet under specific conditions.

Molecular Geometry

Molecular geometry refers to the three-dimensional arrangement of atoms within a molecule. It provides insight into the molecule's shape, size, and polarity, which impact physical and chemical properties.

To predict molecular geometry, start with the Lewis structure to determine the arrangement of electron pairs around the central atom. Each pair influences the shape - be they bonding pairs or lone pairs. For instance, in \(\text{CCl}_4\), the molecule exhibits a tetrahedral geometry since four chlorine atoms are symmetrically arranged around the central carbon atom.

Understanding molecular geometry is vital as it helps predict how molecules will interact with each other in terms of reactivity, biological activity, and physical attributes like boiling and melting points. Techniques like VSEPR (Valence Shell Electron Pair Repulsion) theory assist in visualizing the likely 3D shape based on electron pair interactions.