Problem 39 - Introductory Chemistry Atoms First

Question

Which of the following are elemental substances and which are compounds: chlorine, \(\mathrm{Cl}_{2}\); octane, \(\mathrm{C}_{8} \mathrm{H}_{18} ;\) sulfur, \(\mathrm{S}_{8} ;\) neon, Ne?

Step-by-Step Solution

Answer

Chlorine (\(\mathrm{Cl}_{2}\)) and sulfur (\(\mathrm{S}_{8}\)) are elemental substances, while octane (\(\mathrm{C}_{8} \mathrm{H}_{18}\)) is a compound. Neon (Ne) is also an elemental substance.

Step 1: Substance 1: Chlorine (Cl2)

Chlorine is given the chemical formula \(\mathrm{Cl}_{2}\). This formula indicates that there are two chlorine atoms bonded together in a molecule. Since there is only one type of element (chlorine) present, it is considered an elemental substance.

Step 2: Substance 2: Octane (C8H18)

Octane has the chemical formula \(\mathrm{C}_{8} \mathrm{H}_{18}\). This formula shows that there are eight carbon atoms and eighteen hydrogen atoms in a molecule of octane. Since there are two different elements (carbon and hydrogen) present, octane is considered a compound.

Step 3: Substance 3: Sulfur (S8)

Sulfur is given the chemical formula \(\mathrm{S}_{8}\). This formula indicates that there are eight sulfur atoms bonded together in a molecule. Since there is only one type of element (sulfur) present, it is considered an elemental substance.

Step 4: Substance 4: Neon (Ne)

Neon is given the chemical symbol Ne. This symbol represents a single atom of neon, as there is only one type of element (neon) present. Therefore, neon is an elemental substance. To summarize: - Chlorine (\(\mathrm{Cl}_{2}\)) is an elemental substance. - Octane (\(\mathrm{C}_{8} \mathrm{H}_{18}\)) is a compound. - Sulfur (\(\mathrm{S}_{8}\)) is an elemental substance. - Neon (Ne) is an elemental substance.

Key Concepts

Chemical Formulas

Chemical formulas are like a language for representing the elements and compounds that make up substances. They provide a shorthand way of conveying important information about a molecule's composition. For example:

• In the chemical formula \( \mathrm{Cl}_{2} \), the subscript \(2\) shows that there are two chlorine atoms in the molecule.
• In \( \mathrm{C}_{8} \mathrm{H}_{18} \), the numbers \(8\) and \(18\) indicate the number of carbon and hydrogen atoms, respectively.
• Single elements like neon, which are represented by \( \mathrm{Ne} \), don't need a subscript unless they are part of a compound.

This system allows chemists to quickly explain what kinds of elements and how many atoms are involved in a substance, making it easier to understand their properties and reactions.

Elemental Substances

Elemental substances consist of molecules made up entirely of one type of element. In these cases, atoms of the element bond together to form the substance itself. Consider the following examples:

• \( \mathrm{Cl}_{2} \): Made of two chlorine atoms. Since only chlorine is present, it's an elemental substance.
• \( \mathrm{S}_{8} \): Made of eight sulfur atoms. This uniformity also qualifies it as elemental.
• \( \mathrm{Ne} \): Represented by a single atom of neon, it remains elemental as no other elements are involved.

All of these substances exhibit physical and chemical properties distinct to the element they consist of, like neon's inertness or chlorine's reactivity.

Compound Identification

Identifying compounds involves recognizing combinations of different elements. These elements join together in fixed ratios to form new substances with unique characteristics. For example:

• \( \mathrm{C}_{8} \mathrm{H}_{18} \): This formula for octane shows it contains carbon and hydrogen in a fixed ratio, forming a compound.
• Compounds consist of molecules that look different from their original elements. This means that octane behaves significantly differently from carbon or hydrogen alone.

By analyzing the elements present and their ratios, chemists can determine whether a substance is an elemental or a compound. Octane is identified as a compound due to its mixed elemental nature, which gives it properties unique from the components that form it.

Chemical Bonding

Chemical bonding is the process that holds atoms together within a molecule, whether they form an elemental substance or a compound. There are various types of chemical bonds, including covalent and ionic bonds, which dictate how atoms interact.

• In \( \mathrm{Cl}_{2} \), a covalent bond forms as two chlorine atoms equally share electrons. This makes chlorine stable as an elemental form.
• In a compound like octane, \( \mathrm{C}_{8} \mathrm{H}_{18} \), covalent bonds also exist, but involve different atoms (carbon and hydrogen), resulting in a network of bonds that give octane its properties.

Understanding these bonds is essential, as they determine the structural and chemical behavior of both elemental substances and compounds.