Matter and Its Interactions
Discover the building blocks of our universe and how they interact to form everything around us.
In This Section
Introduction to Matter
Matter is anything that has mass and takes up space. It's all around us—the water we drink, the air we breathe, and the ground we walk on. Matter makes up everything in our physical world, from the tiniest atoms to the largest galaxies.
In middle school physics, we focus on understanding the fundamental properties of matter, how different types of matter interact, and how matter can change form while still following the laws of conservation.
Did You Know?
Despite how solid objects appear, matter is mostly empty space! The atoms that make up matter consist primarily of empty space between the nucleus and electrons.
Atomic Structure
Atoms are the basic building blocks of matter. They're incredibly small—so small that millions of them could fit on the head of a pin! Each atom has a central nucleus made up of protons (positively charged particles) and neutrons (neutral particles), with electrons (negatively charged particles) orbiting around it.
The number of protons in an atom determines which element it is. For example, all hydrogen atoms have 1 proton, all carbon atoms have 6 protons, and all oxygen atoms have 8 protons. The periodic table organizes all elements based on their atomic structure.
Try This!
Build different atoms by adding protons, neutrons, and electrons in our interactive "Build an Atom" simulation. See how changing the number of particles affects the element and its properties.
Try the simulation →States of Matter
Matter exists in different states, primarily solid, liquid, and gas. The state of matter depends on the arrangement and energy of its particles.
Solid
In solids, particles are tightly packed in a regular pattern. They vibrate but don't change position, giving solids a fixed shape and volume.
Liquid
In liquids, particles are close together but can move past each other. Liquids have a fixed volume but take the shape of their container.
Gas
In gases, particles are far apart and move freely in all directions. Gases have neither a fixed shape nor a fixed volume.
Matter can change from one state to another when energy is added or removed. For example, adding heat to ice (solid water) causes it to melt into liquid water. Adding more heat causes the liquid water to evaporate into water vapor (gas).
Properties of Matter
Matter has both physical and chemical properties that help us identify and classify different substances.
Physical Properties
- Mass and weight
- Density
- Color and appearance
- Melting and boiling points
- Hardness and malleability
- Conductivity (thermal and electrical)
- Solubility
Physical properties can be observed or measured without changing the substance's composition.
Chemical Properties
- Reactivity with other substances
- Flammability
- Heat of combustion
- Toxicity
- pH (for solutions)
- Oxidation states
- Electronegativity
Chemical properties describe how a substance interacts with other substances to form new substances.
Real-World Connection
Engineers and scientists use their knowledge of material properties to design everything from bridges and buildings to smartphones and sports equipment. For example, airplane frames use aluminum because it's strong yet lightweight, while cooking pots often use copper because it conducts heat well.
Chemical Reactions
Chemical reactions occur when substances combine or break apart to form new substances with different properties. During a chemical reaction, atoms rearrange, but they are never created or destroyed—this is the law of conservation of mass.
Signs of a Chemical Reaction
Color Change
A change in color often indicates a chemical reaction has occurred.
Gas Formation
Bubbles or fizzing can indicate that a gas is being produced.
Precipitate Formation
A solid forming in a liquid solution is called a precipitate.
Temperature Change
Reactions can release heat (exothermic) or absorb heat (endothermic).
Light Production
Some reactions produce light, like glow sticks or combustion.
Odor Change
New smells can indicate that new substances have formed.
Chemical reactions can be represented by chemical equations, where the substances that react (reactants) are shown on the left side of an arrow, and the substances that form (products) are shown on the right side.
2 H2 + O2 → 2 H2O
This equation shows that two hydrogen molecules combine with one oxygen molecule to form two water molecules.
Thermal Energy Effects
Thermal energy (heat) affects matter in various ways. When matter is heated or cooled, it can undergo physical changes like expansion, contraction, or changes in state.
Phase Changes
| Phase Change | Process | Energy | Example |
|---|---|---|---|
| Melting | Solid → Liquid | Absorbs heat | Ice melting into water |
| Freezing | Liquid → Solid | Releases heat | Water freezing into ice |
| Vaporization | Liquid → Gas | Absorbs heat | Water boiling into steam |
| Condensation | Gas → Liquid | Releases heat | Steam condensing on a cold surface |
| Sublimation | Solid → Gas | Absorbs heat | Dry ice (solid CO₂) turning to gas |
At the molecular level, adding thermal energy increases the motion of particles. In solids, particles vibrate more; in liquids and gases, they move faster. This increased motion can overcome the attractive forces between particles, causing phase changes.
Try This Experiment!
Place an ice cube in a heat-resistant glass and heat it gently. Observe and record the temperature changes as the ice melts and the water eventually boils. Notice that during phase changes (melting and boiling), the temperature remains constant even though heat is being added!
Check Your Understanding
1. What determines which element an atom is?
Answer: The number of protons in the nucleus determines the element.
2. Name the three common states of matter and describe how particles behave in each state.
Answer: Solid (particles are tightly packed in fixed positions), liquid (particles are close but can move past each other), and gas (particles are far apart and move freely).
3. What happens to the temperature of water while it's boiling?
Answer: The temperature remains constant at 100°C (at standard pressure) while water is boiling, even though heat is being added.