If chemistry is the study of matter, then the first step is understanding what matter actually is and how it behaves. Matter makes up everything, from the air you breathe to the screen you’re reading this on. But it isn’t as simple as it seems. Matter exists in different forms, changes in different ways, and follows patterns that shape the world around us.

What Is Matter?

In chemistry, matter is anything that has mass and takes up space.

• Your shoes? Matter.
• A cloud? Matter.
• The invisible air around you? Still matter.

Energy (like heat, sound, or light) isn’t matter, but it interacts with matter constantly. Studying those interactions is what makes chemistry so fascinating.

The States of Matter

You may have learned about solids, liquids, and gases. But there’s also a fourth state: plasma.

1. Solid
   • Definite shape and volume
   • Particles tightly packed, only vibrating in place
   • Examples: ice, wood, metal
2. Liquid
   • Definite volume, but no definite shape (takes the shape of its container)
   • Particles loosely packed, sliding past each other
   • Examples: water, oil, milk
3. Gas
   • No definite shape or volume
   • Particles moving quickly and far apart
   • Examples: oxygen, carbon dioxide
4. Plasma
   • Like gas, but with charged particles
   • Found in stars, lightning, neon signs
   • Fun fact: plasma is the most common state of matter in the universe, though rare on Earth

Properties of Matter

A property is a characteristic that describes a substance. Some are visible at a glance, while others show up only when the substance is changed.

Physical Properties (observed without changing the substance):

• Color
• Texture
• Melting or boiling point
• Density
• Conductivity
  Example: Ice melts into water at 0°C. It’s still H₂O before and after.

Chemical Properties (observed when a substance changes into something new):

• Flammability (does it burn?)
• Reactivity (does it react with water or acid?)
• Corrosiveness (does it rust or break down?)
  Example: Iron rusts when exposed to oxygen and water. That’s a chemical property.

Physical vs. Chemical Changes

Understanding the difference between physical and chemical changes helps chemists know whether something new has been created.

• Physical Change: no new substance forms; usually reversible.
  
  • Examples: freezing water, breaking glass, dissolving salt.

• Chemical Change: a new substance forms; usually not reversible.
  
  • Clues include unexpected color change, bubbles or gas release, heat or light, a new smell, or a solid forming from two liquids.
  • Example: burning paper turns into ash and smoke, which are new substances.

Classifying Matter

Matter can also be classified based on the types of particles it contains.

1. Pure Substances
   
   • Element: one type of atom (helium, iron).
   • Compound: two or more atoms chemically bonded in a fixed ratio (H₂O, CO₂). Compounds have properties different from the elements that make them.
2. Mixtures
   
   • Homogeneous (uniform throughout): also called solutions (salt water, air, brass).
   • Heterogeneous (not uniform): visible different parts (salad, granite, trail mix).

Recap and Real-Life Connections

• Boiling pasta water = physical change. Burning toast = chemical change.
• Clothes are made of compounds like cellulose (cotton) or polymers (polyester).
• The air you breathe is a mixture of gases, mostly nitrogen and oxygen.

Understanding matter means understanding the stuff that makes up your world: its behavior, its changes, and its possibilities.

“Matter is neither created nor destroyed, it just changes form.”

That’s the Law of Conservation of Matter, one of the most important principles in chemistry. And it’s the idea that will keep showing up as you keep learning.