Properties of Elements, Compounds, and Mixtures
Elements: The Building Blocks of Matter
Element
An element is the simplest form of matter that cannot be broken down into simpler substances by physical or chemical means.
- Each element is made up of atoms, which are identical in their number of protons.
- Think of elements as the "purest ingredients" in chemistry.
- Hydrogen (H) is an element that exists as diatomic molecules ($H_2$) in nature.
- Iron (Fe) is an element found in the Earth's crust and is used to make steel.
Key Properties of Elements:
- They consist of only one type of atom.
- They are represented by chemical symbols (e.g., H for hydrogen, O for oxygen).
- They cannot be physically or chemically split into simpler substances.
Use the periodic table to identify elements and their properties, such as atomic number and mass.
Compounds: Chemical Combinations of Elements
Compound
A compound is a substance formed when two or more different elements chemically bond together in fixed proportions.
Unlike mixtures, the components of a compound lose their individual properties and form a new substance with unique characteristics.
Example- Water ($H_2O$) is a compound made of hydrogen and oxygen atoms in a 2:1 ratio.
- It has properties distinct from its constituent elements: hydrogen is explosive, and oxygen supports combustion, but water extinguishes fire.
- Sodium chloride (NaCl), or table salt, is a compound formed by the bonding of sodium (a reactive metal) and chlorine (a toxic gas).
Key Properties of Compounds:
- They have a fixed chemical formula (e.g., $H_2O$, NaCl).
- Their properties differ from the elements they are made of.
- They can only be separated into their elements through chemical reactions.
- Don't confuse mixtures with compounds.
- A mixture of hydrogen and oxygen is not water; it’s just a mixture!
Mixtures: Physical Combinations of Substances
Mixture
A mixture contains two or more elements, compounds, or both that are physically combined but not chemically bonded.
- Each component retains its original properties, and the composition can vary.
- Mixtures can be classified into two types:
- Homogeneous mixtures: Uniform composition throughout (e.g., saltwater, air).
- Heterogeneous mixtures: Non-uniform composition (e.g., oil and water, sand and iron filings).
Key Properties of Mixtures:
- Components are not chemically bonded.
- They can be separated by physical methods (e.g., filtration, distillation).
- The composition can vary (e.g., different concentrations of sugar in tea).
Alloys, such as steel (iron and carbon), are mixtures, not compounds, because their components are not chemically bonded.
Pure Substances vs. Mixtures
Elements and Compounds as Pure Substances
Pure substance
A pure substance consists of only one type of particle with a fixed composition and uniform properties throughout.
- Elements: Made of only one type of atom. Examples: oxygen ($O_2$), iron (Fe).
- Compounds: Made of two or more elements chemically bonded in a fixed ratio. Examples: water ($H_2O$), sodium chloride (NaCl).
Compounds can only be separated into elements by chemical reactions, not physical methods.
Mixtures: Not Pure Substances
- Homogeneous Mixtures: Uniform throughout (e.g., saltwater, air).
- Heterogeneous Mixtures: Non-uniform with distinguishable components (e.g., sand and iron filings).
Separation Techniques: Isolating Components of Mixtures
- Because mixtures are physically combined, their components can be separated using physical methods.
- Let’s explore some common techniques:
Filtration: Separating Solids from Liquids
Filtration
Filtration is used to separate insoluble solids from liquids. For example, sand can be separated from water using filter paper.
How it works:
- Pour the mixture through a funnel lined with filter paper.
- The liquid (filtrate) passes through, leaving the solid (residue) behind.
