Element vs Compound
An element is a pure substance made of only one type of atom; A compound is a substance made of two or more different elements chemically bonded together.
Quick Comparison
| Aspect | Element | Compound |
|---|---|---|
| Definition | Pure substance made of one type of atom | Substance made of two or more elements chemically bonded |
| Composition | Cannot be broken down into simpler substances by chemical means | Can be broken down into elements through chemical reactions |
| Examples | Oxygen (O₂), Carbon (C), Gold (Au), Hydrogen (H₂) | Water (H₂O), Salt (NaCl), Carbon dioxide (CO₂), Glucose (C₆H₁₂O₆) |
| Periodic table | All 118 elements listed on periodic table | Not listed on periodic table; formed by combining elements |
| Properties | Properties match the specific element | Properties differ completely from constituent elements |
| Chemical formula | Single symbol (C, O, Au) or diatomic (O₂, H₂) | Multiple symbols with subscripts (H₂O, CO₂, NaCl) |
Key Differences
1. Atomic Composition
Elements consist of only one type of atom. For example, a piece of pure gold contains only gold atoms (Au). A sample of oxygen gas contains only oxygen molecules (O₂), which are two oxygen atoms bonded together. Elements cannot be broken down into simpler substances by chemical means—only nuclear reactions can split atoms.
Compounds consist of two or more different types of atoms chemically bonded in fixed ratios. Water (H₂O) always contains 2 hydrogen atoms and 1 oxygen atom. Table salt (NaCl) always contains 1 sodium atom and 1 chlorine atom. Compounds can be broken down into their constituent elements through chemical reactions.
2. The Periodic Table
Elements are the building blocks of all matter and are organized in the periodic table. There are 118 known elements (as of 2024), including 94 naturally occurring elements and 24 synthetic elements created in laboratories. Each element has a unique atomic number representing the number of protons in its nucleus.
Compounds are not listed on the periodic table. Instead, they are formed by combining elements from the periodic table. There are millions of known compounds, and new ones are synthesized daily in laboratories worldwide.
3. Properties vs Constituent Parts
Elements have properties that directly reflect the nature of that specific atom. Gold is yellow, malleable, and conducts electricity because those are inherent properties of gold atoms. Carbon can be black (graphite) or clear (diamond) depending on how the carbon atoms are arranged.
Compounds have properties completely different from their constituent elements. Sodium (Na) is a soft, highly reactive metal that explodes in water. Chlorine (Cl) is a toxic yellow-green gas. But when bonded together as sodium chloride (NaCl), you get table salt—a white crystalline solid that's safe to eat and essential for life.
4. Chemical Bonding
Elements in their natural state may exist as single atoms (noble gases like helium, neon) or as diatomic molecules where two atoms of the same element bond together (O₂, H₂, N₂, Cl₂, Br₂, I₂, F₂). These are still elements because they contain only one type of atom.
Compounds form when atoms of different elements share or transfer electrons to achieve stable electron configurations. Ionic compounds (like NaCl) form when electrons transfer from one atom to another. Covalent compounds (like H₂O) form when atoms share electrons.
5. Separation Methods
Elements cannot be separated into simpler substances by chemical reactions. You can change the physical form of an element (melting gold, boiling water into steam) but you cannot break it down chemically. Only nuclear reactions (fusion, fission, radioactive decay) can transform one element into another.
Compounds can be decomposed into their constituent elements through chemical reactions. Electrolysis can split water (H₂O) into hydrogen gas (H₂) and oxygen gas (O₂). Heating can decompose some compounds—for example, heating calcium carbonate (CaCO₃) produces calcium oxide (CaO) and carbon dioxide (CO₂).
Examples and Identification
Elements
- Oxygen (O₂) - gas we breathe
- Carbon (C) - found in coal, diamonds, graphite
- Gold (Au) - precious metal
- Nitrogen (N₂) - makes up 78% of Earth's atmosphere
- Helium (He) - used in balloons
- Iron (Fe) - used in steel production
Compounds
- Water (H₂O) - 2 hydrogen + 1 oxygen
- Table salt (NaCl) - sodium + chlorine
- Carbon dioxide (CO₂) - carbon + 2 oxygen
- Methane (CH₄) - carbon + 4 hydrogen
- Ammonia (NH₃) - nitrogen + 3 hydrogen
- Glucose (C₆H₁₂O₆) - carbon + hydrogen + oxygen
How to Tell Them Apart
Chemical formula has one letter? → Element (e.g., C for carbon, O for oxygen)
Chemical formula has two+ different letters? → Compound (e.g., H₂O, CO₂, NaCl)
Exception: O₂, H₂, N₂ are still elements (same letter) even though they're diatomic molecules.
Properties and Behavior
Elements
Characteristics
- Pure substance with uniform properties throughout
- Listed on periodic table with unique atomic number
- Properties determined by electron configuration
- Cannot be simplified by chemical reactions
- Can exist as atoms or molecules (O₂, H₂)
Classification
- Metals (iron, copper, gold, sodium)
- Nonmetals (oxygen, nitrogen, carbon, sulfur)
- Metalloids (silicon, boron, arsenic)
- Noble gases (helium, neon, argon)
Compounds
Characteristics
- Fixed ratio of elements (H₂O is always 2:1 hydrogen to oxygen)
- Properties differ from constituent elements
- Can be decomposed by chemical reactions
- Formed through chemical bonding (ionic or covalent)
- Millions of possible combinations
Classification
- Ionic compounds (NaCl, MgO, CaCO₃)
- Covalent compounds (H₂O, CO₂, CH₄)
- Organic compounds (contain carbon: glucose, proteins)
- Inorganic compounds (don't contain carbon: salts, acids)