Question

Which class of hydrocarbon has double bonds?

Short answer

Alkenes have double bonds.

Step-by-step solution

Identify Hydrocarbon Classes

Hydrocarbons are organic compounds composed entirely of hydrogen and carbon. The main classes of hydrocarbons include alkanes, alkenes, alkynes, and aromatic hydrocarbons.

Recognize Saturated vs Unsaturated Hydrocarbons

Alkanes are known as saturated hydrocarbons because they contain only single bonds between carbon atoms. Unsaturated hydrocarbons, such as alkenes and alkynes, contain one or more double or triple bonds, respectively.

Determine the Class with Double Bonds

Among the unsaturated hydrocarbons, alkenes are characterized by having at least one carbon-to-carbon double bond. In contrast, alkynes have at least one carbon-to-carbon triple bond.

Key concepts

Organic Compounds

Organic compounds are the foundation of chemistry and life itself. These compounds are primarily made from carbon, a remarkably versatile element that can form stable bonds with many other elements, most commonly hydrogen. This ability allows carbon to create a vast array of complex structures, from very simple molecules to incredibly complex polymers.

Organic chemistry, the study of organic compounds, is centered on carbon's ability to form chains and rings. This creates an infinitive variety of compounds and is why carbon-based life, such as humans, exists. These compounds are crucial in forming and maintaining life, providing everything from energy to structural components. The primary element of organic compounds, carbon, can form up to four covalent bonds, leading to a wide diversity of molecular shapes and sizes.

In the context of hydrocarbons, the simplest type of organic compounds, the variety is further narrowed to structures only containing hydrogen and carbon atoms. Despite this simplicity, hydrocarbons form the basis for more complex molecules and thus hold significant importance in chemistry. These compounds can be classified into several categories, including alkanes, alkenes, alkynes, and aromatic hydrocarbons.

Alkenes

Alkenes play a unique role among the classes of hydrocarbons. They are defined by having at least one carbon-to-carbon double bond in their molecular structure. This double bond is what makes alkenes unsaturated hydrocarbons, distinguishing them from alkanes, which only have single bonds between carbon atoms.

The presence of a double bond in alkenes introduces a special set of properties:

• They are more reactive than alkanes because the double bond is a region of high electron density.
• They can participate in addition reactions where molecules add across the double bond, changing it to a single bond.
• Alkenes have geometric isomers due to the restricted rotation around the double-bond, often leading to cis-trans isomerism.

The simplest alkene is ethene (or ethylene), which has just two carbon atoms and one double bond. Alkenes are not just theoretical constructs; they play a significant role in the production of plastics, like polyethylene, and other important chemicals.

Chemical Bonding

Chemical bonding is the process that holds atoms together in compounds, making it fundamental to the structure and function of organic compounds. In general, bonding happens in several forms. Among hydrocarbons, the primary type of chemical bonding is covalent bonding.

Covalent bonds involve the sharing of electron pairs between atoms. In hydrocarbons, this typically involves the sharing of electrons between carbon atoms or between carbon and hydrogen atoms. With single, double, or triple bonds possible between carbon atoms, the type of bonding defines the molecule's properties:

• Single bonds, as found in alkanes, are called sigma (C3) bonds, providing maximum rotation between bonded atoms.
• Double bonds, seen in alkenes, consist of one sigma bond and one pi (C0) bond. The pi bond restricts rotation, giving rise to different geometric shapes (isomerism).
• Triple bonds, which are in alkynes, contain one sigma bond and two pi bonds, resulting in a linear shape and making alkynes even more reactive than alkenes.

Understanding these bond types is crucial, as they determine how hydrocarbons interact with other substances and their environmental behaviors. This insight is vital when exploring reactions in organic chemistry, helping scientists predict the physical and chemical attributes of organic compounds.