Chemistry Foundations: Matter, Substances, States, Changes, and Energy

What is Chemistry?

Chemistry is a branch of science focused on identifying the substances that make up matter.
It also involves understanding the properties of these substances, how they are composed, how matter changes under different conditions, and how matter interacts with energy.
This course will connect chemistry concepts to real-world examples and other sciences.

What is Matter?

Matter is anything that has mass and takes up space.
Everyday examples include glasses, butterflies, computers, coffee, coffee mugs, and even the sun, clouds, and atmosphere molecules.
The behavior and function of matter in space are determined by the properties of atoms and molecules.

Atoms vs. Molecules

Atoms are the smallest units of matter that retain the properties of the type of matter.
Molecules are two or more atoms bound together.
Example: a pure gold bar is made up of gold atoms; billions of atoms form a single bar.
Analogy: atoms are like LEGO bricks—the smallest unit that remains functional when building larger structures.
- If you cut a Lego brick in half, it won’t function as intended.
- The way LEGO bricks fit together determines the properties of the resulting structure (the molecule).
Water as a molecule: water is made of two hydrogen atoms and one oxygen atom, held together by a chemical bond.
- Each water molecule has a specific shape and arrangement that gives water its properties.
Small changes in atom arrangement can drastically change a molecule’s properties.
- Example:
- Water: $ext{H}_2 ext{O}$ (two H, one O).
- Hydrogen peroxide: $ext{H}2 ext{O}2$ (an extra oxygen atom compared to water) → at certain concentrations, hydrogen peroxide is toxic; used in bleaching agents and as a disinfectant at low concentrations.
Pure water is drinkable; water makes up about $70\%$ of the human body, highlighting the importance of water in chemical reactions and life.
Carbon allotropes: same element (carbon) can form different structures with very different properties.
- Diamond: carbon atoms arranged in a 3D network under high heat/pressure → very hard.
- Graphite: carbon atoms arranged in sheets → softer and lubricious.

Classification of Matter

A substance is a specific instance of matter (e.g., air, water, rock).
State of matter refers to physical form: solid, liquid, or gas.
Composition describes what the substance is made of.

States of Matter

Solid
- Fixed volume and rigid shape.
- Examples: rock, diamond.
- Crystalline solids have atoms/molecules bound in a repeating pattern (e.g., table salt, diamonds).
- Amorphous solids have less order (e.g., glass, plastics).
- Even without external pressure, shapes are retained (e.g., a diamond in a jar retains shape).
Liquid
- Fixed volume but no fixed shape; takes the shape of its container (e.g., water, gasoline, alcohol).
- Particles are less tightly packed than in a solid and can flow.
Gas
- No fixed volume or shape; fills the container.
- Highly energetic and move freely; compressible (e.g., air).
- If you press on a lid, the gas volume can decrease; solids resist compression.
- Gases expand to fill spaces (e.g., balloon expansion).
Temperature drives state changes: increasing temperature tends to disrupt order and increase molecular motion, promoting transitions (solid ↔ liquid ↔ gas).

Pure Substances vs Mixtures

Pure substances contain only one component.
- Examples: pure gold, pure water, table salt (NaCl).
- Elements vs compounds:
- Element: cannot be broken down chemically into simpler substances; composed of one type of atom (e.g., helium, carbon).
- Compound: two or more elements bound in fixed proportions; can be chemically broken down (e.g., water $ext{H}_2 ext{O}$ can be broken into hydrogen and oxygen).
Mixtures contain two or more components in variable proportions.
- Examples: sweet tea (water, tea, sugar); the amounts can vary.
- Not all mixtures have fixed ratios; they can vary by sample.
- Classifications:
- Homogeneous mixture: uniform composition throughout (e.g., iced tea, lemonade, fully mixed pumpkin spice latte). Every sip has the same composition.
- Heterogeneous mixture: non-uniform composition (e.g., wet sand with water; portions differ in concentration).

How to Classify Matter (Practical Guidance)

Look for variability in composition.
- Pure substances: one type of atom or molecule (no variability).
- Mixtures: variability in composition across the sample.
In the lab, pure vs mixture can be confirmed by experiments, not just appearance.
Pure substances can be broken down further:
- Compounds are breakable into elements chemically (e.g., $ext{H}2 ext{O} ightarrow 2 ext{H} + ext{O}2$ in reactions).
- Elements cannot be broken down into simpler substances by chemical means.

Changes of Matter

Matter is constantly changing states and compositions in everyday life (ice melting, iron rusting, gasoline burning, fruit ripening/rotting).
Physical changes: alter appearance or state but not composition.
- Examples:
- Boiling water: $ext{H}2 ext{O(l)} ightarrow ext{H}2 ext{O(g)}$
- Breaking a piece of wood (physical fragmentation): still the same substance.
- Dissolving sugar into water: sugar and water remain present; composition of each component remains the same.
- Sublimation: solid to gas without passing through a liquid phase (e.g., dry ice, $ext{CO}2 ext(s) ightarrow ext{CO}2 ext{(g)}$ ).
Chemical changes: change the composition of matter; new substances form.
- Examples:
- Rust: iron reacts with oxygen (and often water) to form iron oxide.
 - Simple representation: $4 ext{Fe} + 3 ext{O}2 + 6 ext{H}2 ext{O} ightarrow 4 ext{Fe(OH)}_3$ (later dehydrates to magnetite/hematite forms).
- Propane burning: chemical reaction producing CO₂ and H₂O.
 - Balanced equation: $ext{C}3 ext{H}8 + 5 ext{O}2 ightarrow 3 ext{CO}2 + 4 ext{H}_2 ext{O}$
Physical vs chemical changes depend on whether the composition changes; some changes involve energy exchange.

Physical Properties vs Chemical Properties

Physical property: observed without changing the substance’s composition (e.g., smell, temperature, taste, color, melting point, boiling point, density).
Chemical property: observed only when the substance undergoes a chemical change (e.g., reactivity, toxicity, flammability).
- Example: flammability is tested by burning the substance to see if it forms new products.

Energy, Work, and Thermodynamics

Energy: the capacity to do work or transfer heat.
Work: energy transfer due to a force acting through a distance.
- Formula: W = oldsymbol{F} \nolinebreak[4] ext{cdot}
  olinebreak[4] oldsymbol{d} = F d \, \cos\theta
- Example: pushing a box across a floor transfers energy to move the box.
Two main types of mechanical energy:
- Kinetic energy (energy of motion): $KE = \tfrac{1}{2} m v^2$
- Potential energy (stored energy): $PE = m g h$
Total energy is the sum of kinetic and potential energies: $E_{ ext{total}} = KE + PE$
Conservation of energy (First Law of Thermodynamics): energy is never created or destroyed; it is always transferred or transformed, not lost or gained overall.
- A common compact expression: $\Delta E = q + w$ where q is heat transfer and w is work done on/by the system.
Systems tend to move from higher potential energy (unstable) to lower potential energy (stable).
- Example: a high-energy gas molecule participating in a combustion reaction releases energy to power motion or work.
- In fuels like gasoline, chemical energy stored in molecules is released during combustion to perform useful work (e.g., powering vehicles).
Chemical energy is the energy stored in chemical bonds; this class emphasizes chemical energy as a key type of energy to study in reactions.
Practical takeaways:
- Energy changes accompany physical and chemical changes; energy is conserved overall.
- Systems with high potential energy tend to become more stable by releasing energy to the surroundings.
- Energy transfers can take forms such as heat, work, or changes in kinetic/potential energy of substances.

Connections to Real-World Relevance

Water as a life-supporting substance: water makes up a majority of body mass and participates in many reactions and transport processes.
Energy and fuels: understanding chemical energy in molecules explains how fuels power engines.
Material properties: crystal vs amorphous structures explain why some materials are hard (diamond) while others are glass or plastic.
Energy conservation and efficiency: the first law underpins engineering, heating/cooling systems, and environmental considerations.

Quick Takeaways

Chemistry studies matter: what it is, what it’s made of, and how it changes with energy.
Matter exists as solids, liquids, or gases; substances can be pure (elements or compounds) or mixtures (homogeneous or heterogeneous).
Changes can be physical (no composition change) or chemical (composition changes).
Energy relates to work and transformations; the total energy is conserved; systems tend to move toward lower potential energy and greater stability.
Real-world examples anchor concepts: water, hydrogen peroxide, carbon allotropes, sublime dry ice, combustion of propane, rust, and dissolving sugar.

Examples and Equations to Remember

Water and hydrogen peroxide:
- $ext{H}2 ext{O}$ vs $ext{H}2 ext{O}_2$ to illustrate how an extra oxygen atom changes properties.
Water as a major body component:
- $70\%$ of the body is water.
Balanced combustion of propane:
- $ext{C}3 ext{H}8 + 5 ext{O}2 ightarrow 3 ext{CO}2 + 4 ext{H}_2 ext{O}$
Basic energy formulas:
- $KE = \tfrac{1}{2} m v^2$
- $PE = m g h$
- $E_{ ext{total}} = KE + PE$
Work and energy transfer:
- $W = \boldsymbol{F} \cdot \boldsymbol{d} = F d \cos \theta$
First Law of Thermodynamics (conceptual): $\Delta E = q + w$

If you have any specific topic you’d like me to expand or add worked examples for, tell me and I’ll tailor the notes further.