Chemistry

The science of matter — atoms, molecules, and transformations

What Is Chemistry?

Chemistry studies the composition, properties, and behavior of matter — how substances combine, change, and interact with energy. It sits at the bridge between physics and biology.

Fundamental Concepts

• Atoms — the smallest unit of an element; made of protons, neutrons, and electrons
• Elements & the Periodic Table — 118 known elements organized by atomic number and properties
• Chemical Bonds — ionic, covalent, and metallic bonds hold atoms together
• Moles & Stoichiometry — counting atoms by weighing them (1 mole = 6.022 × 10²³ particles)
• States of Matter — solid, liquid, gas, plasma

Types of Reactions

• Synthesis — A + B → AB
• Decomposition — AB → A + B
• Single Replacement — A + BC → AC + B
• Double Replacement — AB + CD → AD + CB
• Combustion — fuel + O₂ → CO₂ + H₂O + energy

The Periodic Table

Organized by atomic number (proton count), the table groups elements with similar properties into columns (groups) and rows (periods). Key trends: electronegativity, atomic radius, and ionization energy increase or decrease predictably across the table.

Branches of Chemistry

• Organic Chemistry — carbon-based compounds (fuels, plastics, drugs)
• Inorganic Chemistry — metals, minerals, salts
• Physical Chemistry — thermodynamics, quantum chemistry, kinetics
• Biochemistry — chemistry of living systems
• Analytical Chemistry — identifying and quantifying substances