Question

Complete these structural formulas by adding enough hydrogens to complete the tetravalence of each carbon. Then write the molecular formula of each compound.

Short answer

Question: Complete the structural formula and write the molecular formula of the following compound: ``` CH3-CH2-CH ``` Answer: The completed structural formula of the compound is: ``` H H H | | | CH3-CH2-CH3 | | | H H H ``` The compound has 3 carbon atoms and 8 hydrogen atoms, so the molecular formula for this compound is C3H8.

Step-by-step solution

Complete the structural formula

Identify the number of carbon atoms in the given compound and the bonds they have already formed. Add enough hydrogen atoms to satisfy the tetravalence of each carbon atom, making sure that the total number of bonds formed by each carbon atom equals four. Draw the completed structural formula for the compound.

Write the molecular formula

Count the total number of carbon (C) and hydrogen (H) atoms present in the completed structural formula. Then, write the molecular formula of the compound using the format CH_x_y_, where x represents the number of carbon atoms and y represents the number of hydrogen atoms.

Example: Completing the structural formula and finding the molecular formula of a compound

Let's say that we have a compound with this structural formula: ``` CH3-CH2-CH2 ``` Step 1: Find the number of carbon atoms and the bonds they have formed. The compound has three carbon atoms. To complete the tetravalence, we need to add a hydrogen atom to the terminal carbon atoms, like this: ``` H H H | | | CH3-CH2-CH2-H | | | H H H ``` Step 2: Count the number of carbon and hydrogen atoms in the completed formula. There are 3 carbon and 8 hydrogen atoms. The molecular formula for this compound would be C3H8. You would apply this same process to complete the structural formulas and determine the molecular formulas of all other given compounds.

Key concepts

Tetravalence of Carbon

In organic chemistry, tetravalence of carbon is a critical concept that refers to the ability of carbon atoms to form four covalent bonds with other atoms. This property is due to the four valence electrons in carbon's outer shell, which it can share with other atoms to achieve a stable electron configuration.

When visualizing the structure of organic molecules, it's essential to ensure that each carbon atom forms exactly four bonds. This may include single, double, or triple bonds and even bonds to other carbon atoms or different elements like hydrogen, oxygen, and nitrogen. For example, if a carbon atom is already bonded to two other carbons, then it will only need two hydrogens to fulfill its tetravalence. Understanding this concept is essential when analyzing and creating structural formulas for organic compounds.

For instance, in a hydrocarbon chain, if a carbon atom is bonded to two neighboring carbon atoms, we need to add two hydrogen atoms to that carbon to satisfy its tetravalence, as seen in chemical structures where carbons are connected in a chain or ring formation. It's this feature that allows carbon to form a vast array of compounds, the basis of organic chemistry.

Molecular Formula

A molecular formula is a way of expressing the number and type of atoms in a molecule but does not detail the bonds or structure of the atom. It serves as a shorthand notation that conveys essential information about the composition of the organic compound. For example, the molecular formula \( CH_4 \) represents methane, indicating that there is one carbon atom and four hydrogen atoms in the molecule.

The molecular formula is particularly useful for summarizing the overall composition of large molecules. It tells us how many atoms of each element are present in the compound but does not give any indication of the molecule's structure. To write the molecular formula, as shown in the exercise, one counts the total number of each type of atom in the completed structural formula of the compound. This count is then represented in the format \( C_xH_y \), where \( x \) is the number of carbon atoms and \( y \) is the number of hydrogen atoms.

Organic Compound Representation

The representation of organic compounds can be done in several ways, with structural formulas being one of the most informative methods. Structural formulas provide a two-dimensional depiction of the molecule, showing the arrangement of atoms and the covalent bonds between them. This approach can highlight the tetravalence of carbon and different functional groups in the compound.

Structural formulas can vary in complexity; they can be displayed as simple lines indicating bonds between the atoms, or as detailed drawings showing the position of every atom. For instance, a line drawing may represent a carbon-to-carbon bond as a single line (—), and carbon-to-hydrogen bonds are implied when not explicitly drawn out. However, these simplified structures should always be interpreted with the understanding that each carbon atom forms four bonds.

When analyzing or creating structural formulas, it’s crucial to know that carbon atoms can connect in chains or rings, which can contain single, double, or triple bonds, and understanding these various representations is fundamental in organic chemistry. This visual language allows chemists to convey complex structural information in an efficient and understandable manner.