What Is a Chemical? Definition and Examples

What is a chemical? In science, a chemical is any substance with a specific composition, whether it’s a single element or a compound of multiple elements. While people often think of “chemicals” as synthetic or harmful substances, the truth is that everything around you, including water, air, and even your own body, consists of chemicals. Understanding what a chemical is forms the foundation of chemistry and helps explain everything from cooking to climate change.

Key Takeaways: What Is a Chemical?

• A chemical is any substance with a definite composition and distinct properties.
• All matter is made of chemicals, regardless of whether it is natural or synthetic.
• Chemicals can be elements, compounds, or mixtures.
• The term “chemical” is often misunderstood and unfairly associated with danger.
• Both physical and chemical properties help identify chemicals.
• Chemistry involves transforming chemicals via chemical reactions.

Chemical Definition

In everyday usage, a “chemical” often refers to an undesirable additive or contaminant. For example, pesticides in water or artificial colorings in food are “chemicals.” But, chemistry sees chemicals somewhat differently.

A chemical is a substance with a specific composition. It is an element, an alloy, or a compound made up of two or more elements combined in a fixed ratio. For instance, water (H₂O) is a chemical because it consists of hydrogen and oxygen combined in a 2:1 ratio. All matter either is a chemical or else consists of chemicals.

Natural vs. Synthetic Chemicals

Some chemicals occur in nature, while others are synthesized. Some chemicals occur both from natural and manmade processes. For example, vitamin C (ascorbic acid) synthesized in a lab is chemically identical to vitamin C found in an orange. What differs is the source and not the chemical itself.

• Natural Chemicals: These are chemicals that occur in nature without human intervention. For example, fruits produce citric acid naturally.
• Synthetic Chemicals: Humans make synthetic chemicals via chemical reactions. A common example is plastic, which comes from petrochemicals.

It’s worth noting that the distinction between “natural” and “synthetic” doesn’t necessarily equate to “safe” and “dangerous.” Many natural chemicals are harmful, and many synthetic chemicals are perfectly safe. For example, arsenic is a natural element that is poisonous, while baking soda (sodium bicarbonate) is a synthetic chemical that we use in baking all the time.

Natural doesn’t always mean safe, and synthetic doesn’t always mean harmful.

Types of Chemicals

Chemicals come in various forms depending on their composition, structure, and how they interact with other substances. Understanding the main types of chemicals helps classify the substances we encounter in the lab, in industry, and in everyday life.

1. Elements

An element is a pure substance that consists of only one type of atom. Elements are the simplest substances that cannot be broken down by ordinary chemical means. Each element has a unique number of protons in its nucleus, called the atomic number. Examples include:

• Hydrogen (H) – the lightest and most abundant element.
• Iron (Fe) – a metal used in construction and tools.
• Oxygen (O) – essential for respiration.

2. Compounds

A compound is a chemical substance formed when two or more different elements chemically bond in a fixed ratio. The atoms in a compound are held together by chemical bonds (ionic, covalent, or metallic), and the compound has different properties than the individual elements. Examples include:

• Water (H₂O) – a compound of hydrogen and oxygen.
• Carbon dioxide (CO₂) – a compound of carbon and oxygen.
• Table salt (NaCl) – formed from sodium and chlorine.

3. Alloys

An alloy is a homogeneous mixture of two or more elements, usually metals. Although alloys are technically mixtures, they behave like single substances with consistent properties. Examples include:

• Brass – a mixture of copper and zinc.
• Steel – mostly iron, with carbon and other elements.

4. Polymers

Polymers are large molecules composed of repeating structural units called monomers. These can occur naturally or be synthetically produced. Examples include:

• DNA – the polymer that carries genetic information.
• Cellulose – found in plant cell walls.
• Polyethylene – a common plastic used in bags and containers.

5. Mixtures

While not single chemicals, mixtures consist of two or more chemicals that are physically combined but not chemically bonded. The components retain their individual properties and can often be separated by physical methods. Examples include:

• Air – a mixture of gases like nitrogen, oxygen, and carbon dioxide.
• Seawater – water with dissolved salts and minerals.
• Granite – a rock composed of quartz, feldspar, and mica.

6. Solutions

A solution is a homogeneous mixture in which one substance (solute) is uniformly dissolved in another (solvent). Though technically a mixture, a solution behaves like a single chemical phase. Examples:

• Saltwater – salt (solute) dissolved in water (solvent).
• Vinegar – acetic acid dissolved in water.

Understanding these different categories helps scientists and students alike recognize and classify the substances they work with, analyze, or encounter in daily life.

Pure Chemical vs. Mixture

Chemicals occur on their own or in combination with other chemicals:

• Pure Chemical: A pure chemical or pure substance has a constant composition and cannot be separated into its constituent elements by physical methods. For example, pure water, regardless of its source, always has two hydrogen atoms bonded to one oxygen atom. However, chemical and nuclear reactions change chemicals into other chemicals.
• Mixture: A mixture, on the other hand, consists of two or more substances that are physically combined but not chemically combined. This means each substance in a mixture retains its own chemical properties. Air is an example of a mixture, which consists of oxygen, nitrogen, carbon dioxide, and other gases mixed together without any specific ratio. A bag of candies is another mixture example.

Mixture vs. Chemical Reaction

Mixtures and chemical reactions often get confused, but they’re fundamentally different:

• When substances form a mixture, they don’t change their identities. For instance, when you mix sugar and water, you can still separate and retrieve the original sugar and water through processes like evaporation.
• In a chemical reaction, substances react to form new substances with different properties. This involves breaking and forming chemical bonds. For example, when hydrogen gas reacts with oxygen gas, it forms water. Once formed, the water does not return to its original gases without another chemical reaction. Baking a cake also involves a chemical reaction. Chemically, the composition of a cake differs from that of its ingredients.

Examples: Chemical or Not?

While all matter consists of chemicals, not everything is a chemical.

• Chemicals: Water, oxygen, glucose, sodium chloride, vinegar, sterling silver, helium, gold. Chocolate is a mixture of chemicals (cocoa, sugar, fat). Carbon dioxide is a compound (which is a type of chemical).
• Not Chemicals: Light, heat, sound. These are forms of energy, not matter. Fire is a chemical reaction that involves chemicals, but is not itself a chemical. Thoughts, emotions, and dreams emerge from chemical activity in the brain, but they are not chemicals themselves.

The Role of Chemicals in Everyday Life

Chemicals play a pivotal role in our daily lives:

1. Medicine: Many medicines are chemicals formulated to treat specific illnesses. For example, aspirin is a chemical that relieves pain.
2. Food: Chemical reactions are at the heart of cooking. For example, baking soda reacts with acids in vinegar or fruit juice to produce carbon dioxide, making cakes and bread rise.
3. Digestion: The body uses chemical reactions for turning food into chemical energy and raw resources for growth and repairing tissues.
4. Cleaning: Household cleaners contain chemicals that kill bacteria, remove stains, and clean surfaces.
5. Environment: Photosynthesis, a natural chemical reaction, is how plants convert carbon dioxide into oxygen, which is essential for life on Earth.
6. Energy: Combustion, another chemical reaction, releases energy from fuels. It provides heat, plus the energy aids in electricity production.
7. Technology: Semiconductors, battery chemicals, circuit board etchants.
8. Agriculture: Fertilizers, pesticides, soil pH regulators.
9. Construction: Concrete chemistry, paints, sealants.

Identifying Chemicals

Because a chemical has a consistent composition, it has characteristic properties that identify it. Both physical and chemical properties help identify chemicals.

Physical Properties

Physical properties are apparent without changing the chemical identity of a substance. Here are some common physical properties:

• Color: The visual appearance of a substance. For example, copper has a reddish-brown color.
• Odor: The smell of a substance. For instance, ammonia has a pungent odor.
• Density: The mass of a substance per unit volume.
• Melting Point: The temperature at which a solid turns into a liquid.
• Boiling Point: The temperature at which a liquid turns into a gas.
• Solubility: The ability of a substance to dissolve in another substance. For example, sugar is soluble in water.
• Malleability: The ability of a substance to be hammered or rolled into sheets.
• Ductility: The ability of a substance to be drawn into wires.
• Conductivity: The ability of a substance to conduct electricity or heat.
• State of Matter: Whether a substance is solid, liquid, or gas at a given temperature and pressure.

Chemical Properties

Chemical properties describe how a substance interacts with other substances, i.e., its ability to undergo chemical changes. These properties only become apparent during a chemical reaction. Some examples include:

• Reactivity: How readily a substance reacts, often with respect to another substance. For example, sodium reacts violently with water.
• Flammability: The ability of a substance to ignite or burn.
• Oxidation: How a substance reacts with oxygen. Rusting of iron is an example of oxidation.
• Acidity/Basicity (pH): Determines if a substance is acidic, basic, or neutral.
• Toxicity: How harmful a substance is to organisms.

How Chemists Identify Chemicals

Identifying a chemical substance involves determining its composition and structure, often by using a combination of physical observations and analytical techniques. Chemists rely on both qualitative and quantitative methods to identify unknown substances or verify known ones.

1. Physical Properties

Physical properties help identify a chemical without changing its identity. Common techniques include:

• Melting and boiling point analysis – Pure substances have characteristic melting and boiling points.
• Density measurement – Calculated by mass divided by volume.
• Color and odor – These offer initial clues, though they are often subjective.
• Solubility tests – Determine if a substance dissolves in water or other solvents.

2. Chemical Properties

Testing chemical reactivity reveals how a substance behaves with others:

• Litmus or pH testing – Indicates if a substance is acidic, basic, or neutral.
• Reaction with known substances – For example, bubbling when adding acid may indicate a carbonate.
• Combustion or oxidation tests – Determines flammability and oxidation states.

3. Instrumental Techniques

Chemists use laboratory instruments to gather precise, often molecular-level information:

a. Spectroscopy

• Infrared (IR) spectroscopy – Identifies types of chemical bonds.
• UV-Visible spectroscopy – Reveals conjugated systems and concentration of solutions.
• Nuclear Magnetic Resonance (NMR) – Shows how atoms are arranged within a molecule.
• Mass spectrometry (MS) – Determines molecular mass and structure.

b. Chromatography

• Separates mixtures into individual components. Common types include:
  • Gas Chromatography (GC)
  • High-Performance Liquid Chromatography (HPLC)
  • Paper or Thin-Layer Chromatography (TLC)

c. X-ray Crystallography

• Reveals the exact three-dimensional arrangement of atoms in a crystalline compound.

d. Elemental Analysis

• Determines the percentage of each element in a compound.

4. Reference Tools

Chemists also use standardized databases and labeling systems for identifying and categorizing substances:

• CAS Numbers – Each chemical has a unique Chemical Abstracts Service number.
• Safety Data Sheets (SDS) – Contain standardized information about a chemical’s identity, hazards, and handling.
• IUPAC Nomenclature – Provides systematic names for chemical compounds.

Identifying chemicals correctly is essential in research, manufacturing, environmental science, medicine, and many other fields. Proper identification ensures safety, accuracy, and scientific reproducibility.

References

• IUPAC (1997). “Chemical Substance.” Compendium of Chemical Terminology (the “Gold Book”) (2nd ed.). Oxford: Blackwell Scientific Publications. doi:10.1351/goldbook.C01039
• Petrucci, Ralph H.; Herring, F. Geoffrey; Madura, Jeffry D.; Bissonnette, Carey (2011). General Chemistry: Principles and Modern Applications. Pearson Canada. ISBN 9780137032129.