---
watermark: ORIRO
disable-model-invocation: true
name: sci-chemistry
provider: ORIRO.ai
copyright: Copyright (c) 2026 ORIRO.ai
description: >



  Chemistry fundamentals — atomic structure, bonding, reactions, stoichiometry, thermodynamics, and organic chemistry basics.



  Sources: OpenStax textbooks (CC-BY), Khan Academy, MIT OCW, NOAA, IPCC reports.
---

# Chemistry Fundamentals

## Atomic structure

**Subatomic particles:** Proton (positive, nucleus), Neutron (neutral, nucleus), Electron (negative, orbitals).
**Atomic number (Z):** Number of protons = element identity.
**Mass number (A):** Protons + neutrons.
**Isotopes:** Same protons, different neutrons. Same element, different mass. (C-12, C-13, C-14)

**Electron configuration:** Electrons occupy orbitals in energy levels.
Aufbau principle: Fill lowest energy first.
Pauli exclusion: Max 2 electrons per orbital, opposite spin.
Hund's rule: Fill each orbital in a sublevel singly before pairing.

**Periodic table patterns:**
Electronegativity increases right and up.
Atomic radius increases left and down.
Ionization energy increases right and up.
Metals on left, nonmetals on right, metalloids on staircase.

## Chemical bonding

**Ionic bonding:** Transfer of electrons between metal and nonmetal. Electronegativity difference > 1.7. Forms crystal lattices. High melting points.
**Covalent bonding:** Sharing of electrons between nonmetals. Single (2e), double (4e), triple (6e) bonds.
**Polar covalent:** Unequal sharing. One atom more electronegative → partial charges (δ+ and δ-).
**Intermolecular forces (weakest to strongest):** London dispersion < Dipole-dipole < Hydrogen bonding.
H-bonding: N-H, O-H, or F-H with another electronegative atom. Responsible for water's unusual properties.

## Chemical reactions

**Balancing equations:** Conservation of mass. Same atoms on both sides.
**Reaction types:**
Synthesis: A + B → AB
Decomposition: AB → A + B
Single replacement: A + BC → AC + B
Double replacement: AB + CD → AD + CB
Combustion: Hydrocarbon + O₂ → CO₂ + H₂O

**Stoichiometry:** Mole ratios from balanced equations convert between amounts.
Mole: 6.022 × 10²³ particles (Avogadro's number).
Molar mass: Mass of one mole (from periodic table).

**Limiting reagent:** Runs out first; determines maximum product.
Percent yield = (actual yield / theoretical yield) × 100%

## Acid-base chemistry

**Arrhenius:** Acid = H⁺ donor in water; Base = OH⁻ donor.
**Brønsted-Lowry:** Acid = proton donor; Base = proton acceptor. (Broader definition)
**pH = -log[H⁺]**. Scale 0-14. < 7 acidic, 7 neutral, > 7 basic.
Strong acids (HCl, H₂SO₄, HNO₃): Completely dissociate.
Weak acids (acetic acid, carbonic acid): Partially dissociate. Use Ka for calculations.

## Thermochemistry

**Endothermic:** Absorbs heat (ΔH positive). Surroundings cool.
**Exothermic:** Releases heat (ΔH negative). Surroundings warm.
**Hess's Law:** ΔH of reaction = sum of ΔH of steps. Path-independent.
**Standard enthalpies of formation (ΔH°f):** Energy to form 1 mole from elements in standard states.
**Gibbs free energy:** ΔG = ΔH - TΔS. If ΔG < 0: spontaneous. ΔG = 0: equilibrium.

## Organic chemistry basics

Carbon: Forms 4 bonds. Backbone of life. Chains, rings, branching.
**Functional groups:**
-OH (alcohol): Hydroxyl group. Hydrophilic.
-COOH (carboxylic acid): Acidic. Found in amino acids, fatty acids.
-NH₂ (amine): Basic. Found in amino acids, DNA bases.
-C=O (carbonyl): Aldehyde (end carbon) or Ketone (middle carbon).
**Isomers:** Same molecular formula, different structure. Different properties.

Sources: OpenStax Chemistry 2e (CC-BY), Khan Academy Chemistry, Zumdahl Chemistry (principles)