compound definition in chemistry

2 min read 13-03-2025

What is a Compound?

A compound is a substance formed when two or more chemical elements are chemically bonded together. This bonding results in a new substance with properties different from its constituent elements. Crucially, these elements are combined in a fixed ratio, and this ratio can be expressed using a chemical formula. For example, water (H₂O) is a compound consisting of two hydrogen atoms and one oxygen atom.

Key Characteristics of Compounds

Fixed Ratio of Elements: Compounds always contain the same elements in the same proportions. This is a defining characteristic that distinguishes them from mixtures.
Chemical Bonding: Elements in a compound are held together by chemical bonds – either ionic, covalent, or metallic bonds – creating a stable structure.
New Properties: The properties of a compound are different from the properties of the elements that make it up. For example, sodium (Na) is a highly reactive metal, and chlorine (Cl) is a poisonous gas. However, their combination forms sodium chloride (NaCl), or table salt, a harmless crystalline solid.
Chemical Formulas: Compounds are represented by chemical formulas which show the type and number of atoms of each element present. The formula for water, H₂O, shows it contains two hydrogen atoms and one oxygen atom.
Decomposition: Compounds can be broken down into simpler substances (elements or other compounds) through chemical reactions. This process is called decomposition.

Types of Chemical Bonds in Compounds

The type of bond holding atoms together in a compound dictates its properties.

1. Ionic Bonds

Ionic bonds are formed through the electrostatic attraction between oppositely charged ions. One atom loses electrons (becoming a positively charged cation) and another atom gains those electrons (becoming a negatively charged anion). Table salt (NaCl) is a classic example, with sodium losing an electron to chlorine.

2. Covalent Bonds

Covalent bonds involve the sharing of electrons between atoms. This creates a strong bond, resulting in molecules. Water (H₂O) is a prime example of a covalent compound, with oxygen sharing electrons with two hydrogen atoms.

3. Metallic Bonds

Metallic bonds occur in metals, where electrons are delocalized and shared among many atoms. This accounts for the properties of metals like conductivity and malleability. While less common in compounds, alloys are examples of materials with metallic bonding between different metal elements.

Distinguishing Compounds from Mixtures

It's important to distinguish compounds from mixtures. Mixtures are simply physical combinations of substances, where the components retain their individual properties. They do not have fixed ratios and can be separated using physical methods (like filtration or distillation). For instance, saltwater is a mixture of water and salt, easily separated through evaporation. In contrast, the properties of salt (NaCl) are distinct from sodium and chlorine, and it cannot be easily separated into its constituent elements physically.

Examples of Compounds

Many everyday substances are compounds:

Water (H₂O): Essential for life.
Carbon Dioxide (CO₂): A greenhouse gas.
Sodium Chloride (NaCl): Table salt.
Glucose (C₆H₁₂O₆): A simple sugar.
Ammonia (NH₃): Used in fertilizers.
Sulfuric Acid (H₂SO₄): A strong acid used in industry.

Further Exploration: Molecular and Ionic Compounds

Compounds can be further classified as molecular or ionic. Molecular compounds consist of discrete molecules held together by covalent bonds. Ionic compounds are composed of ions held together by electrostatic forces. This distinction often impacts their physical properties like melting and boiling points.

Understanding the definition of a compound is fundamental to grasping the basics of chemistry. It lays the groundwork for exploring the vast world of chemical reactions and the properties of matter.