Problem 95 - Introductory Chemistry Atoms First

Question

Which one of the following is a compound: ozone, 18 -karat gold (made by melting gold and other metals together), \(\mathrm{NaCl}\), liquid nitrogen, iced tea?

Step-by-Step Solution

Answer

The compound among the given options is \(\mathrm{NaCl}\) (sodium chloride), as it is formed by the chemical bonding of two different elements, sodium and chlorine, in a 1:1 ratio. The other options are not compounds, as they consist of only one element or are mixtures without chemical bonding.

Step 1: Analyze ozone

Ozone is a molecule made up of three oxygen atoms bonded together, represented by the chemical formula \(\mathrm{O_3}\). This means ozone consists of only one element, oxygen, even though it has multiple atoms of the same element joined together. Therefore, ozone is not a compound but instead is a type of molecule called an allotrope (different forms of the same element).

Step 2: Analyze 18-karat gold

18-karat gold is made by melting gold and other metals together, such as silver and copper, to create an alloy. In an alloy, the individual atoms of the different metals mix together, but they do not form chemical bonds. Therefore, 18-karat gold is not a compound but a type of mixture called an alloy.

Step 3: Analyze \(\mathrm{NaCl}\)

\(\mathrm{NaCl}\), known as sodium chloride, is a compound formed by the combination of two elements, sodium (Na) and chlorine (Cl). These elements form a chemical bond in a 1:1 ratio, resulting in a new substance with unique properties compared to its constituent elements. Therefore, \(\mathrm{NaCl}\) is a compound.

Step 4: Analyze liquid nitrogen

Liquid nitrogen is a substance composed of nitrogen molecules (\(\mathrm{N_2}\)) in the liquid state. Nitrogen molecules consist of two nitrogen atoms bonded together. Since liquid nitrogen only consists of one element, nitrogen, it is not a compound. Liquid nitrogen is considered a diatomic molecule (a molecule consisting of two atoms of the same element) in the liquid state.

Step 5: Analyze iced tea

Iced tea is a mixture of various substances, including water, tea, sugar, and possibly other ingredients, such as flavorings or additives. These individual components do not form chemical bonds with each other, and therefore iced tea is not a compound but a type of mixture.

Step 6: Conclusion

Among the given options, only \(\mathrm{NaCl}\) (sodium chloride) is a compound, as it is formed by the chemical bonding of two different elements, sodium and chlorine, in a 1:1 ratio. The other options (ozone, 18-karat gold, liquid nitrogen, and iced tea) are not compounds, as they either consist of only one element (in different forms) or are mixtures of various substances without chemical bonding.

Key Concepts

Allotropes

Allotropes are fascinating forms of elements where the atoms of a single element arrange themselves differently to create distinct substances. A classic example is oxygen, which can take the form of

• oxygen gas (\(\mathrm{O_2}\)),
• ozone (\(\mathrm{O_3}\)).

These all share the same type of atom but have different structures and properties. This difference in atomic arrangement leads to variations in characteristics, such as physical appearance and chemical activity.

By understanding allotropes, we grasp that an element can exist in multiple states, each serving unique functions in science and nature. Embracing the diversity of allotropes can enhance our appreciation of the dynamic nature of chemistry.

Mixtures

Mixtures are combinations of two or more substances where each substance retains its own chemical identity and properties. When we think of mixtures, it's helpful to remember:

• They can be homogeneous, where the composition is uniform throughout, like iced tea.
• They can be heterogeneous, where the composition varies, such as a salad.

In mixtures, the substances are physically combined, meaning they can still be separated by physical methods like filtration or distillation.

A mixture does not involve any chemical bonding between its components, which differentiates it from compounds. Everyday examples like 18-karat gold, which is an alloy, illustrate how different substances can blend without losing their individual properties.

Chemical Bonds

Chemical bonds are the attractive forces that hold atoms together in molecules or compounds. They occur when atoms share or transfer electrons, aiming to achieve a more stable electron configuration. The main types of chemical bonds include:

• Ionic bonds, where electrons are transferred, seen in \(\mathrm{NaCl}\).
• Covalent bonds, where electrons are shared, like in water (\(\mathrm{H_2O}\)).
• Metallic bonds, characterized by a lattice of positive ions surrounded by free electrons, as found in metals.

Chemical bonds are crucial as they define the structure and properties of compounds. They determine how atoms combine and interact to form new substances with unique properties.

Elements and Atoms

Elements are pure substances consisting entirely of one type of atom. They are the building blocks of matter and are represented on the periodic table. Each element has a unique atomic structure that defines its chemical behavior.

For example, oxygen, designated as \(\mathrm{O}\), is an element made up of atoms, each with 8 protons in its nucleus.

• Atoms are the smallest units of an element, retaining all the chemical properties of that element.
• Atoms consist of protons, neutrons, and electrons.

Understanding elements and atoms is foundational to studying chemistry, as interactions between atoms lead to the formation of molecules and compounds, which are the core of chemical reactions and processes.