Fun Fact Intro: Imagine a tiny world, too small to be seen, where everything we know starts to make sense! That's the world of atoms and molecules. Even the smell of your barbecue gets its start there. 😊

• Democritus (400 BCE): Thought about the existence of atoms, but it took ages for people to catch on!
• 19th Century - John Dalton: Noticed elements mixed in specific patterns. Suggested atoms might be behind this mystery.

Real-World Example: Think of making a cake! The recipe asks for exact amounts of each ingredient, just like elements combine in fixed ratios.

• We still can't snap a pic of a gas molecule doing its thing.
• But, effects like diffusion and Brownian motion give us hints!

Real-World Example: BBQ smells! When you cook, the smell travels everywhere even without wind - thanks to diffusion. Air molecules shuffle around the yummy food vapours.

• Bromine gas and air in separate jars.
• Remove the divider, and bromine gas goes up. Why? Air molecules play bumper cars with bromine molecules and push some upwards.

• Robert Brown (1827): Spotted small particles in water bouncing around like crazy.
• Experiment: Smoke particles in a cell are seen zigzagging unpredictably. Invisible air molecules hit these smoke particles, transferring momentum.

Real-World Example: It's like a dance floor! The air molecules are energetic dancers bumping into the smoke particles, making them change their dance moves.