Question

A dictionary defines the word "compound" as a "combination of two or more parts." What are the "parts" of a chemical compound? Identify three pure (or nearly pure) compounds you have encountered today. What is the difference between a compound and a mixture?

Short answer

The parts of a compound are chemically bonded elements. Common compounds encountered today are water (H₂O), salt (NaCl), and carbon dioxide (CO₂). A compound has a fixed composition, unlike a mixture.

Step-by-step solution

Understanding a Chemical Compound

A chemical compound consists of atoms of two or more different elements that are chemically bonded together. The 'parts' of a chemical compound refer to these different elements that make up the compound. For example, in water (H₂O), the parts are hydrogen and oxygen.

Examples of Pure Compounds

Identify common pure compounds you might encounter daily: 1. Water ( H_2O ), which is used for drinking and cleaning. 2. Sodium chloride (NaCl), commonly known as table salt, used in cooking. 3. Carbon dioxide (CO₂), exhaled in breathing and dissolved in carbonated drinks.

Distinguishing Compounds from Mixtures

A compound is a substance formed when two or more elements are chemically bonded together and has distinct properties and a fixed composition. In contrast, a mixture is a combination of two or more substances that are not chemically bonded, can vary in composition, and retain their original properties. Examples of mixtures include saltwater or air, where components are physically combined.

Key concepts

Elements

Elements are the building blocks of matter, and they are pure substances that cannot be broken down into simpler substances by chemical means. Each element is made up of atoms that share the same number of protons in their nuclei. For instance, the element hydrogen ( H ) consists solely of hydrogen atoms. Elements are fundamental because they combine in various ways to form the vast array of substances we encounter daily.
Every element is represented by a unique symbol in the periodic table, like O for oxygen or He for helium. The elements are organized in the table based on their atomic number, which is the number of protons each has.
Elements exhibit unique chemical properties:

• Metals, like iron and copper, are typically solid at room temperature and conduct electricity.
• Nonmetals, such as oxygen and nitrogen, can be gases, liquids, or solids, and do not conduct electricity well.
• Metalloids, like silicon, have properties that are intermediate between metals and nonmetals.

Understanding elements helps explain the nature and structure of the compounds they form.

Chemical Bonds

Chemical bonds are the forces that hold atoms together to form compounds. There are several types of chemical bonds, and each type affects the properties of the resulting compound. Two primary types of bonds include ionic and covalent bonds.

Ionic Bonds: These bonds occur when electrons are transferred from one atom to another, leading to the formation of ions. An example is sodium chloride ( NaCl ), where a sodium atom donates an electron to a chlorine atom, resulting in a positive sodium ion and a negative chloride ion. The attraction between these oppositely charged ions constitutes the ionic bond.

Covalent Bonds: In covalent bonds, atoms share pairs of electrons. A common example is the water molecule ( H_2O ), where each hydrogen atom shares an electron with the oxygen atom, resulting in a stable molecule. Covalent bonding typically occurs between nonmetals.
Chemical bonds govern many of the fundamental properties of compounds, such as melting point, electrical conductivity, and solubility.

Mixtures vs Compounds

Mixtures and compounds are two ways in which elements and compounds can physically and chemically interact. Understanding the difference between them is crucial in studying chemistry.
Mixtures: In a mixture, two or more substances are combined physically, not chemically. They retain their individual properties, and the combination can be easily separated through physical means like filtration or distillation. For example, air is a mixture of gases like nitrogen and oxygen, where each retains its original character.

• Mixtures can be homogeneous, like saltwater, where the composition is uniform, or
• heterogeneous, like a salad, where different components are visible.

Compounds: On the other hand, compounds involve chemical bonds. When elements form a compound, they do so through a chemical reaction creating a substance with new properties distinct from the individual elements. This means the individual components cannot be separated by physical methods.
In essence, while mixtures are physical blends, compounds are chemical creations with specific formulas, like water ( H_2O ) or carbon dioxide ( CO_2 ). Understanding these differences not only helps in chemistry but also in practical applications like cooking or pharmaceuticals.