Problem 7 - Chemistry The Central Science In Si Units

Question

Indicate whether each statement is true or false. (a) All carbon atoms in propene are \(s p^{2}\) hybridized. (b) Acetone is another name for propanone. (c) The phenyl group contains six \(s p^{2}\) -hybridized carbons. (d) A hydrocarbon containing only \(s p^{3}\) carbons must be an alkane.

Step-by-Step Solution

Answer

(a) False, (b) True, (c) True, (d) True.

Step 1: Analyze Statement (a)

In propene (C₃H₆), examine the hybridization of each carbon atom. The structure is important here: it has a double bond between two carbons. The carbon atoms in a double bond are usually sp² hybridized. The third carbon, attached by a single bond, is sp³ hybridized. So, not all carbon atoms in propene are sp² hybridized.

Step 2: Analyze Statement (b)

Examine chemical naming conventions. Acetone is the common name for propanone. Both names refer to the same substance with the chemical formula (CH₃)₂CO. Therefore, acetone is indeed another name for propanone.

Step 3: Analyze Statement (c)

Consider benzene, which forms the phenyl group when a hydrogen is removed. Benzene has a hexagonal ring where each carbon is bonded with a double bond, making them all sp² hybridized. Therefore, the phenyl group contains six sp² hybridized carbons.

Step 4: Analyze Statement (d)

Understand the structure of hydrocarbons. A hydrocarbon where all the carbon atoms have sp³ hybridization can only contain single bonds. Therefore, such a hydrocarbon is classified as an alkane.

Key Concepts

Carbon Hybridization

In organic chemistry, carbon hybridization refers to the process by which atomic orbitals of carbon mix to form new hybrid orbitals. These hybrid orbitals influence the geometry and shape of organic molecules.
Carbon, although usually depicted with four bonds in organic molecules, can form different hybridized states:

• sp³: This hybridization involves one "s" orbital and three "p" orbitals combining to form four equivalent sp³ hybrid orbitals, leading to a tetrahedral shape. This is observed in methane (CH₄).
• sp²: In this state, one "s" orbital and two "p" orbitals mix, forming three sp² hybrid orbitals that lie on a plane, giving a trigonal planar shape. "Benzene" or propene are prime examples.
• sp: In sp hybridization, one "s" and one "p" orbital mix, forming two linear shaped orbitals. This is seen in acetylene (C₂H₂).

Hybridization helps predict the shape, bond angle, and reactivity of molecules.

sp2 vs sp3 Hybridization

The difference between sp² and sp³ hybridization is fundamental in determining the geometry and properties of organic compounds.
In sp² hybridization, there are three hybrid orbitals formed from the mixing of one s and two p orbitals.

• These orbitals lie flat on a plane with a 120-degree angle between each, contributing to structures with double bonds like ethene or aromatic systems like benzene.
• The remaining unhybridized "p" orbital is involved in extending the pi bond formation, which adds significant rigidity and limits rotation around the bond.

Conversely, sp³ hybridization creates four equivalent orbitals positioned in a tetrahedral arrangement.

• This results usually in a 109.5-degree angle between each bond, characteristic of single-bonded molecules like alkanes.
• sp³ hybridized systems have greater flexibility and allow free rotation around single bonds.

Recognizing these differences aids in predicting molecular behavior and how they interact chemically.

Organic Chemistry Nomenclature

Understanding organic chemistry nomenclature is vital to identifying and differentiating compounds. Organic compounds often have systematic names determined by specific rules:

• The root name is based on the longest carbon chain present in the compound. For example, "prop" in propanone indicates a three-carbon chain.
• Functional groups are indicated by suffixes and prefixes. For instance, the "-one" in propanone highlights the ketone functional group.
• Common names are often used for well-known compounds, such as "acetone" for propanone.

Simplifying these rules helps in translating complex chemical formulas into easily understandable names, allowing chemists to accurately convey and recognize substances.

Hydrocarbon Classification

Hydrocarbons, compounds composed only of carbon and hydrogen, are classified based on bond type and saturation.

• Alkanes are saturated hydrocarbons with single bonds, all carbons being sp³ hybridized. Examples include methane (CH₄) and ethane (C₂H₆).
• Alkenes have at least one double bond and exhibit sp² hybridization in the carbon atoms involved in the double bond. Propene (C₃H₆) is a simple alkene.
• Alkynes contain at least one triple bond with the involved carbons undergoing sp hybridization, seen in acetylene (C₂H₂).
• Aromatics, a special class with a resonating ring structure, exhibit sp² hybridization and are found in compounds like benzene.

Each class has distinct properties and reactivity, influencing their role in chemical reactions and industrial applications.