Matter & Atoms

What you’ll learn

• Matter has mass and volume; the particle model explains solids, liquids, and gases through motion and attractions.
• Elements are one kind of atom; compounds combine different elements in fixed ratios; most phase changes are physical.
• Physical changes alter form or state; chemical changes produce new substances with new properties.
• Density ρ = m/V compares how much matter is packed into a space; sinking/floating follows density differences.
• Heating usually makes particles move faster and solids expand slightly; cooling contracts, linking hot vs cold metal to particle motion.