What is a Compound?
In chemistry, a compound is a substance formed when two or more different chemical elements are chemically bonded together in a fixed ratio. Unlike mixtures, compounds have distinct properties from the elements that compose them and can only be broken down into simpler substances by chemical reactions.
Key Characteristics of Compounds:
- Fixed Ratio: The elements in a compound are always present in fixed, definite proportions by mass. For example, water (H₂O) always has two hydrogen atoms for every one oxygen atom.
- New Properties: When elements form a compound, they lose their individual properties and the compound acquires entirely new properties. Think of sodium (a reactive metal) and chlorine (a toxic gas) combining to form table salt (NaCl), a safe, edible solid.
- Chemical Separation: Compounds cannot be separated into their constituent elements by simple physical means (like filtering or evaporation). They require chemical reactions to break the bonds holding them together.
Click to reveal: What is a chemical element?
A chemical element is a pure substance consisting only of atoms that all have the same numbers of protons in their atomic nuclei. Examples include hydrogen (H), oxygen (O), carbon (C), and gold (Au).
Click to reveal: What is a chemical bond?
A chemical bond is a lasting attraction between atoms, ions or molecules that enables the formation of chemical compounds. These bonds can be ionic (transfer of electrons) or covalent (sharing of electrons).
Visualizing a Compound
Imagine two different types of atoms joining together to form a new, stable unit:
In this simplified diagram, 'Atom A' and 'Atom B' represent two different elements. The line connecting them symbolizes a chemical bond, forming a new substance: 'Compound AB'.
Can table salt (Sodium Chloride, NaCl) be separated back into sodium and chlorine by dissolving it in water and then filtering the water out?
Click for Answer
No, you cannot. While dissolving it in water is a physical process, separating the sodium (Na) and chlorine (Cl) from each other within the salt requires a chemical reaction (like electrolysis). Dissolving merely separates the ions in solution; it doesn't break the chemical bond between Na and Cl to return them to their elemental forms.
Common Examples of Compounds:
- Water (H₂O): Hydrogen and Oxygen
- Carbon Dioxide (CO₂): Carbon and Oxygen
- Sodium Chloride (NaCl): Sodium and Chlorine (Table Salt)
- Glucose (C₆H₁₂O₆): Carbon, Hydrogen, and Oxygen