Question

(a) Is the compound \(\mathrm{CH}_{3} \mathrm{CH}=\mathrm{CH}_{2}\) saturated or unsaturated? Explain. (b) What is wrong with the formula \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}=\mathrm{CH}_{3}\) ?

Short answer

(a) The compound \(\mathrm{CH}_{3} \mathrm{CH}=\mathrm{CH}_{2}\) is unsaturated because it has a double bond between the second and third carbon atoms. Unsaturated compounds have at least one double or triple bond between carbon atoms. (b) The issue with the formula \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}=\mathrm{CH}_{3}\) is that the third carbon atom exceeds its valency by forming 5 covalent bonds, which is not possible. Carbon atoms have a valency of 4, but the third carbon atom in this formula forms a total of 5 bonds (a single bond with the second carbon atom and a double bond with the fourth carbon atom).

Step-by-step solution

Identify the type of bonds

To determine if a compound is saturated or unsaturated, we need to look at the type of bonds between carbon atoms. Single bonds are considered saturated while double or triple bonds are considered unsaturated.

Analyze the given compound

The compound given is \(\mathrm{CH}_{3} \mathrm{CH}=\mathrm{CH}_{2}\). We can notice that there is a double bond between the second and third carbon atoms.

Determine saturation

Since there is a double bond present in the compound, it is considered to be an unsaturated compound.

Explain the result

Unsaturated compounds have at least one double or triple bond between carbon atoms. The presence of double bond between carbon atoms in the given compound \(\mathrm{CH}_{3} \mathrm{CH}=\mathrm{CH}_{2}\) makes it unsaturated. (b) Identify the problem with the formula

Examine the carbon atoms and their bonds

The given formula is \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}=\mathrm{CH}_{3}\). In this formula, there is an issue with the third carbon atom. It forms a double bond with the fourth carbon atom while also having a bond with the second carbon atom.

Determine the valency of the carbon atoms

Carbon atoms have a valency of 4 because they have 4 electrons in their outermost shell, and they can form 4 covalent bonds. In the given formula, the third carbon atom forms a total of 5 bonds (a single bond with the second carbon atom and a double bond with the fourth carbon atom). This exceeds the valency of carbon.

Identify the issue with the formula

The issue with the formula \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}=\mathrm{CH}_{3}\) is that the third carbon atom exceeds its valency by forming 5 covalent bonds, which is not possible.

Key concepts

Carbon Bonds

Carbon atoms can form different types of bonds depending on their structure, which leads to the classification of compounds as saturated or unsaturated.
When carbon atoms are connected by only single bonds, the compound is said to be saturated. These single bonds allow for maximum hydrogen atoms to attach to the carbon chain.
On the other hand, unsaturated compounds have carbon atoms connected by double or triple bonds. These multiple bonds leave fewer positions available for hydrogen atoms.

• Single bonds are represented by a single line between atoms, for example, \(-C-C-\).
• Double bonds use two lines, for example, \(-C=C-\), symbolizing that two pairs of electrons are shared.
• Triple bonds are shown with three lines, for example, \(-C≡C-\).

The presence of these multiple bonds not only affects the compound's saturation but also introduces flexibility and reactivity, especially in the case of double and triple bonds.

Valency of Carbon

Valency refers to the ability of an atom to form bonds with other atoms. Carbon is remarkable because it has a valency of 4. This is due to the presence of four electrons in its outer shell. Consequently, carbon can establish a total of four covalent bonds with other atoms, allowing for a vast array of compounds.

• A carbon atom may form four single bonds, such as in methane (\( ext{CH}_4 \)), where it connects with four hydrogen atoms.
• Alternatively, it can form a double bond with another carbon atom and two single bonds with hydrogen atoms, as seen in ethene (\( ext{C}_2 ext{H}_4 \)).
• Carbon can also participate in forming triple bonds, as with nitrogen in hydrogen cyanide (\( ext{HCN} \)), where it forms one single bond and one triple bond.

In forming compounds, each carbon atom must satisfy this rule, making it crucial to correctly balance molecular structures. If a carbon atom attempts to exceed this valency, such as forming five bonds, it violates chemical norms and would result in an impossible structure.

Chemical Formulas

Chemical formulas are a method of accurately representing compounds using symbols and numbers to convey the composition. Each element in a compound is signified by its chemical symbol, and the subscripts indicate the number of atoms of each element in the molecule.

• In the compound \( ext{CH}_3 ext{CH}= ext{CH}_2 \), the formula indicates the presence of three carbon atoms and six hydrogen atoms. The double bond between the second and third carbons signifies it's unsaturated.
• For the compound \( ext{CH}_3 ext{CH}_2 ext{CH}= ext{CH}_3 \), the issue arises as the carbon bonding does not adhere to established rules, causing an error in structural representation, as seen in our exercise solution.

Using chemical formulas provides clarity but requires careful attention to detail to ensure all connections correspond to the chemical and physical laws of bonding.