Chemistry

Chemistry is the study of matter — what it’s made of, how it behaves, and how it changes. It underlies cooking, medicine, materials, and life itself.

Atoms and Elements

All matter is made of atoms. An atom is the smallest unit of a chemical element.

Elements are pure substances made of only one type of atom. There are 118 known elements, organized in the periodic table. Common ones Chad will encounter:

Element	Symbol	Found In
Hydrogen	H	Water (H₂O), fuel
Carbon	C	All living things, diamonds, graphite
Nitrogen	N	Air (78%), proteins
Oxygen	O	Air (21%), water, breathing
Sodium	Na	Table salt (NaCl), nerve function
Iron	Fe	Steel, blood (hemoglobin)
Calcium	Ca	Bones, teeth, dairy
Gold	Au	Jewelry, currency, electronics

Molecules and Compounds

Atoms bond together to form molecules. When different elements bond, the result is a compound.

Examples:

H₂O (water) — 2 hydrogen + 1 oxygen
CO₂ (carbon dioxide) — 1 carbon + 2 oxygen (exhaled by humans, absorbed by plants)
NaCl (table salt) — sodium + chlorine
C₆H₁₂O₆ (glucose/sugar) — carbon, hydrogen, oxygen

Chemical Reactions

A chemical reaction is when atoms rearrange to form new compounds. This involves:

Reactants (what you start with) → Products (what you end up with)
Energy is absorbed or released

Everyday chemical reactions:

Cooking — heat causes chemical changes in food (proteins denature, sugars caramelize)
Burning — rapid oxidation releasing energy and light (fire)
Rusting — slow oxidation of iron
Digestion — breaking down food molecules (How Your Body Works)
Photosynthesis — plants convert CO₂ and water into glucose using sunlight

States of Matter (Chemical View)

See Physics Basics for states (solid, liquid, gas). Chemistry explains why — it’s about intermolecular forces:

In solids: molecules held tightly in place
In liquids: molecules slide past each other
In gases: molecules move freely with lots of space between them

pH Scale: Acids and Bases

The pH scale measures how acidic or basic (alkaline) a substance is:

0–6: Acidic (0 = most acidic)
7: Neutral
8–14: Basic/Alkaline (14 = most basic)

Substance	pH
Battery acid	~1
Lemon juice	~2
Coffee	~5
Pure water	7
Blood	~7.4
Baking soda	~9
Bleach	~13

Human blood is slightly alkaline. If it deviates much from 7.4, it’s a medical emergency.

Chemistry in Daily Life

You interact with chemistry constantly:

Cooking is applied chemistry
Medicines are chemical compounds
Cleaning products rely on chemical reactions
Plastics, fabrics, electronics are engineered materials
The air you breathe is a chemical mixture