Draw dot diagrams for the reactants and products in each equation, and indicate which bonds are broken and which bonds are formed: (a) \(\mathrm{CH}_{4}+\mathrm{I}_{2} \rightarrow \mathrm{CH}_{3} \mathrm{I}+\mathrm{HI}\) (b) \(\mathrm{C}_{2} \mathrm{H}_{4}+\mathrm{F}_{2} \rightarrow \mathrm{FCH}_{2} \mathrm{CH}_{2} \mathrm{~F}\)

Chemical bonding is the force that holds atoms together in compounds. Atoms can bond together in various forms, such as ionic, covalent, and metallic bonds. The Lewis dot structure is a visual representation of the valence electrons in an element, indicating the potential for bonding.

In a Lewis dot structure, the chemical symbol of an element is surrounded by dots that represent its valence electrons. These electrons are the ones involved in bonding and chemical reactions. When drawing Lewis dot structures for molecules in a reaction, as seen with methane (CH4) and iodine (I2), we aim to illustrate how atoms share or transfer electrons to achieve stability, often resembling the nearest noble gas configuration.

For example, in the reaction between methane and iodine, the Lewis structure highlights the breaking of a C-H bond and an I-I bond, leading to the formation of new C-I and H-I bonds. This exchange demonstrates the interaction of valence electrons that leads to the formation of a new chemical product with different properties.

Molecular geometry refers to the three-dimensional arrangement of atoms within a molecule. Understanding the shape of a molecule is crucial as it influences both physical and chemical properties such as boiling point, polarity, and reactivity. Lewis dot structures serve as a foundation for predicting molecular geometry.

The VSEPR (Valence Shell Electron Pair Repulsion) theory is commonly used to predict the geometry of a molecule. According to VSEPR theory, electron pairs around a central atom will arrange themselves to be as far apart as possible to minimize repulsion. For instance, methane (CH4) adopts a tetrahedral geometry to appropriately space out the hydrogen atoms around the central carbon.

Similarly, in the reaction converting ethene (C2H4) to 1,2-difluoroethane (FCH2CH2F), the geometry changes from planar due to the double bond to a staggered tetrahedral arrangement when single bonds are formed. This change in geometry is not only a consequence of the broken and formed bonds but also reflects the electron pair repulsions in the new molecule.

Chemical reactions involve the reorganization of atoms and their respective bonds, converting reactants to products. These processes are governed by the breaking of bonds in the reactants and the formation of new bonds in the products, conservatively following the law of conservation of mass. Translating a chemical reaction into a Lewis dot framework further clarifies these intricate transformations.

In the reactions given as examples, we have a substitution reaction where methane reacts with iodine to form methyl iodide and hydrogen iodide, and an addition reaction where ethene reacts with fluorine to form 1,2-difluoroethane. The Lewis structures demonstrate that in each case, specific bonds are broken (C-H, I-I, C=C, and F-F) and new ones are formed (C-I, H-I, and C-F).

Identifying the bonds that participate directly can help in predicting the outcome of a chemical reaction, in understanding energy changes associated with bond breaking and making, and in recognizing the shift in molecular structure from reactants to products that characterizes chemical transformation. The Lewis dot structures thus provide a simplified yet valuable tool for visualizing and understanding these dynamic changes.