Chemistry Basics: Elements and Compounds

Substances

Elements

• A substance that consists of only one type of atom
• Cannot be broken down into simpler substances by chemical means
• Examples: Hydrogen (H), Carbon (C), Oxygen (O)
• Represented by a one- or two-letter symbol (e.g. H, C, O)
• Around 118 known elements, listed in the periodic table

Compounds

• A substance that consists of two or more different elements
• Formed by chemical reaction between elements
• Properties different from its constituent elements
• Examples: Water (H2O), Carbon Dioxide (CO2), Ammonia (NH3)
• Can be broken down into simpler substances by chemical means
• Formula represents the ratio of atoms of each element in the compound

Mixtures

• A physical blend of two or more substances
• Can be elements, compounds, or both
• No chemical reaction occurs between components
• Properties vary depending on the proportion of each component
• Examples: Air (oxygen, nitrogen, others), Soil (dirt, water, air), Blood (water, proteins, cells)
• Can be separated by physical means (filtration, sedimentation, etc.)

Substances

Elements

• Consist of only one type of atom
• Cannot be broken down into simpler substances by chemical means
• Examples include Hydrogen (H), Carbon (C), and Oxygen (O)
• Represented by a one- or two-letter symbol
• There are around 118 known elements, listed in the periodic table

Compounds

• Consist of two or more different elements
• Formed by chemical reaction between elements
• Have properties different from their constituent elements
• Examples include Water (H2O), Carbon Dioxide (CO2), and Ammonia (NH3)
• Can be broken down into simpler substances by chemical means
• Formula represents the ratio of atoms of each element in the compound

Mixtures

• A physical blend of two or more substances
• Can be elements, compounds, or both
• No chemical reaction occurs between components
• Properties vary depending on the proportion of each component
• Examples include Air (oxygen, nitrogen, others), Soil (dirt, water, air), and Blood (water, proteins, cells)
• Can be separated by physical means (filtration, sedimentation, etc.)

Elements

• Consist of only one type of atom
• Cannot be broken down into simpler substances by chemical means
• Examples: hydrogen (H), oxygen (O), carbon (C)
• Can exist in various forms (allotropes) with different physical properties, but same chemical properties
• 118 known elements, with 92 occurring naturally and 26 being synthetic

Compounds

• Formed by the chemical combination of two or more different elements
• Have properties different from their constituent elements
• Composition always remains the same, with a fixed ratio of elements
• Examples: water (H2O), carbon dioxide (CO2), sodium chloride (NaCl)
• Can be broken down into simpler substances by chemical means

Mixtures

• Physical blends of two or more substances, maintaining their chemical properties
• Composition can vary, with no fixed ratio of substances
• Examples: air (oxygen, nitrogen, etc.), alloys (brass, steel, etc.), sand
• Can be separated by physical means, such as filtration, evaporation, or magnetism