6.1 Classification of Matter
Matter can be classified into elements and compounds based on its chemical composition.
Atoms and Molecules
- Atom: The smallest particle of an element that can take part in a chemical reaction. An atom consists of subatomic particles:
- Protons: Positively charged particles ($+$) located in the nucleus.
- Neutrons: Neutral particles (no charge) located in the nucleus.
- Electrons: Negatively charged particles ($-$) orbiting the nucleus in shells.
- Molecule: A neutral group of two or more atoms chemically bonded together (e.g., $O_2$, $H_2O$).
Elements and Compounds
- Element: The simplest form of matter consisting of only one type of atom. It cannot be broken down into simpler substances by physical or chemical methods (e.g., Gold, Oxygen, Copper).
- Compound: A substance consisting of two or more different elements chemically combined together in a fixed ratio (e.g., Water $H_2O$, Carbon Dioxide $CO_2$, Table Salt $NaCl$).
6.2 The Periodic Table
The Periodic Table is an organized arrangement of elements in order of increasing proton number.
Structure of the Periodic Table
- Periods: The horizontal rows in the Periodic Table (numbered 1 to 7). Elements in the same period have the same number of electron shells.
- Groups: The vertical columns in the Periodic Table (numbered 1 to 18). Elements in the same group have similar chemical properties because they have the same number of valence electrons.
Classification of Elements
Elements in the Periodic Table are broadly classified into three categories:
- Metals: Located on the left and middle of the Periodic Table (e.g., Sodium, Magnesium, Iron, Gold).
- Shiny surface appearance.
- Good conductors of heat and electricity.
- High melting and boiling points.
- Malleable (can be hammered into sheets) and ductile (can be drawn into wires).
- Non-metals: Located on the right side of the Periodic Table (e.g., Oxygen, Carbon, Chlorine, Helium).
- Dull surface appearance.
- Poor conductors of heat and electricity (insulators), except carbon in the form of graphite.
- Low melting and boiling points.
- Brittle in solid state.
- Metalloids: Located along the zigzag line separating metals and non-metals (e.g., Silicon, Germanium). Possess intermediate properties of both metals and non-metals (often act as semiconductors).
6.3 Mixtures and Compounds
Mixtures
A mixture consists of two or more substances (elements or compounds) physically mixed together without any chemical bond. Examples include air, soil, seawater, and brass.
Separation Techniques for Mixtures
Since components in a mixture are physically combined, they can be separated using physical methods:
- Filtration: Separates an insoluble solid from a liquid (e.g., sand from water).
- Evaporation: Obtains a dissolved solid solute from a solution by heating away the liquid solvent (e.g., salt from salt solution).
- Distillation: Separates liquids with different boiling points or recovers a pure solvent from a solution.
- Magnetic Separation: Separates magnetic materials (e.g., iron filings) from non-magnetic substances.
- Chromatography: Separates small quantities of soluble substances based on their differing solubilities in a solvent (e.g., dye pigments in ink).
- Sedimentation / Decantation: Allows heavy insoluble particles to settle at the bottom before pouring off the liquid.
Comparison Between Mixtures and Compounds
- Formation: Mixtures form via physical process; Compounds form via chemical reaction.
- Chemical Bonding: No chemical bonds in mixtures; Strong chemical bonds in compounds.
- Properties: A mixture retains the properties of its original components; A compound has completely new physical and chemical properties different from its constituent elements.
- Separation: Mixtures can be separated by physical methods; Compounds can only be broken down by chemical methods (e.g., electrolysis).