Introduction to Atomic Theory

Grade 10 Science Understanding the Building Blocks of Matter

What is an Atom?

The smallest unit of matter that retains element properties Made up of subatomic particles So small that billions could fit on the period at the end of this sentence Everything around us is made of atoms

Timeline of Atomic Theory Development

Dalton's Atomic Theory (1803)

{"left":"All matter is made of tiny, indivisible particles called atoms\nAtoms of the same element are identical in mass and properties\nAtoms of different elements have different masses and properties","right":"Atoms cannot be created or destroyed in chemical reactions\nCompounds form when atoms combine in simple whole-number ratios\nThis theory explained the law of conservation of mass"}

Thomson's Plum Pudding Model (1897)

Discovered electrons using cathode ray experiments Proposed atoms are spheres of positive charge Electrons embedded throughout like raisins in pudding First model to include subatomic particles

Model Building Challenge

Work in pairs to create physical models Use clay and small objects to represent: • Dalton's solid sphere model • Thomson's plum pudding model Compare and discuss differences Present your models to the class

Think-Pair-Share

If atoms are mostly empty space (as we'll learn next), why does matter feel solid? Discuss with your partner for 2 minutes Be ready to share your ideas with the class

Key Takeaways

Atomic theory has evolved over time through scientific discovery Dalton established atoms as building blocks of matter Thomson discovered atoms contain smaller particles (electrons) Scientific models help us understand invisible phenomena Next: We'll explore Rutherford's surprising discoveries about atomic structure