Democritus to John Dalton's Atomic Theory
Over 2400 years ago, Greek philosopher Democritus proposed that all matter is made of tiny particles called "atomos" (indivisible). In 1805, English chemist John Dalton formalized this into the modern Atomic Theory! Modern Scanning Tunnelling Electron Microscopes (STM) now provide direct visual evidence for Dalton's model.
2400 Years Ago: Democritus
Coined the word "atomos" (indivisible). He explained that different materials had different properties based on particle shape and texture.
1805: John Dalton & Modern Evidence (STM)
Dalton published his mathematical atomic model. Today, Scanning Tunnelling Electron Microscopes (STM) produce actual sub-nanometer images of individual atoms!
Dalton's 5 Core Postulates (1805)
Tiny Indivisible Atoms
All matter is made up of tiny particles called atoms that cannot be broken down further.
Identical Element Atoms
The atoms in an element are all identical, but each element has its own distinct type of atom.
Conservation of Atoms
Atoms are indestructible and cannot be created or destroyed in any chemical process.
Fixed Compound Ratios
In compounds, each atom of an element is always joined to a fixed number of atoms of other elements.
Reactions Rearrange Atoms (No Mass Change)
During chemical reactions (such as fireworks burning), atoms rearrange to make new substances. Because no atoms are gained or lost, there is no change in mass!
Metal vs. Non-Metal Physical Properties
Compare physical properties of key elements used in fireworks (Magnesium, Copper, Sulfur, Bromine).
Magnesium Metal
Used for white sparkler flares- Appearance: Silvery solid
- Melting Point: 650°C (High)
- Mechanical: Malleable & Ductile
- Conductivity: Good Conductor
Copper Metal
Used for blue fireworks flames- Appearance: Browny / Reddish solid
- Melting Point: 1083°C (Very High)
- Mechanical: Malleable & Ductile
- Conductivity: Good Conductor
Sulfur Non-Metal
Key fuel in gunpowder mixtures- Appearance: Yellow solid
- Melting Point: 115°C (Low)
- Mechanical: Brittle (breaks easily)
- Conductivity: Insulator (poor conductor)
Bromine Non-Metal
Used in flame retardants & colored smoke- Appearance: Red-brown liquid
- Melting Point: -7.2°C (Very Low)
- Mechanical: Brittle when solid
- Conductivity: Insulator (poor conductor)
Summary: How Students Can Distinguish Metals vs. Non-Metals
| Property | Metals (e.g., Mg, Cu) | Non-Metals (e.g., S, Br) |
|---|---|---|
| State & Appearance | Shiny solids (silvery / reddish brown) | Dull solids or liquids (yellow, red-brown) |
| Melting Point | High (e.g., 650°C to 1083°C) | Low (e.g., 115°C down to -7.2°C) |
| Malleable & Ductile | Yes (can bend/shape without breaking) | No (Brittle - breaks easily) |
| Electrical & Heat Conductivity | Good Conductors | Insulators (poor conductors) |
IUPAC Global Symbols
Dalton drew circles with patterns, but today scientists use standard 1 or 2 letter IUPAC symbols (First letter CAPITAL). This allows scientists from all countries to communicate regardless of language!
Physical Properties & Changes
Physical Properties: Unique traits of a substance on its own (Colour, Melting point, Boiling point, Density, Electrical/Heat conduction, Malleability, Ductility).
Physical Changes: Changes of state (e.g. Ice $\rightarrow$ Water $\rightarrow$ Steam). No new substances are formed, mass remains constant, and it is easily reversible!