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Chemistry — Essential Concepts

Periodic trends, bonding, stoichiometry, gas laws, and acid/base chemistry — every Chemistry CBE essential on one page.

10 minTEKS 5A,7A,8A,9A,10AChemistry

Chemistry CBE quick-reference — periodic trends, bonding, mole math, gas laws, and acid-base chemistry.

Periodic Trends

  • Atomic radius: increases down a group, decreases across a period
  • Ionization energy: opposite (decreases down, increases across)
  • Electronegativity: increases up + right (fluorine highest)
  • Metallic character: increases down + left
Atom — nucleus (protons + neutrons) with electron shellsp⁺n⁰e⁻ (electrons)

Bonding

  • Ionic: metal + nonmetal; electron transfer (NaCl)
  • Covalent: nonmetal + nonmetal; electron sharing (H₂O)
  • Metallic: sea of electrons (Fe)
  • Polarity: electronegativity difference > 0.4 → polar covalent

Naming & Formulas

  • Ionic: name cation first, then anion (-ide for monatomic)
  • Polyatomics: NO₃⁻ nitrate, SO₄²⁻ sulfate, PO₄³⁻ phosphate, NH₄⁺ ammonium, OH⁻ hydroxide
  • Acids: HCl hydrochloric, H₂SO₄ sulfuric, HNO₃ nitric, CH₃COOH acetic

The Mole

  • 1 mole = 6.022 × 10²³ particles (Avogadro's number)
  • Molar mass: from periodic table (g/mol)
  • Moles = mass / molar mass
  • STP: 1 mol gas = 22.4 L

Stoichiometry

  1. Balance equation
  2. Convert mass → moles using molar mass
  3. Use mole ratio from balanced equation
  4. Convert moles → desired unit (mass, volume, particles)

Limiting reactant: whichever runs out first based on ratios.

Periodic table — metals (blue), metalloids (orange staircase), nonmetals (red)1234567891011121314151617181234567Metals (Li, Fe, Cu, Au, ...)Metalloids (B, Si, Ge, As, Sb, Te)Nonmetals (H, C, N, O, halogens, noble gases)Metalloids form the "staircase" separating metals from nonmetals(Lanthanides & actinides omitted for clarity — sit in period 6 and 7)

Gas Laws

  • Ideal gas: PV = nRT (R = 0.0821 L·atm/mol·K)
  • Combined: P₁V₁/T₁ = P₂V₂/T₂
  • Boyle (constant T): PV = constant
  • Charles (constant P): V/T = constant
  • Always use Kelvin (K = °C + 273)

Acid-Base

  • pH = −log[H⁺]; pH + pOH = 14
  • Acid: pH < 7, donates H⁺; Base: pH > 7, accepts H⁺ or donates OH⁻
  • Strong acids fully dissociate (HCl, H₂SO₄, HNO₃); weak acids partially
  • Neutralization: acid + base → salt + water

Thermochemistry & Kinetics

  • Exothermic: releases heat (ΔH < 0)
  • Endothermic: absorbs heat (ΔH > 0)
  • Activation energy: minimum energy to start reaction; catalysts lower it
  • Reaction rate ↑ with temperature, concentration, surface area

Common Test Mistakes

  • Forgetting to balance the equation before stoichiometry
  • Using °C instead of K in gas laws
  • Mixing up ionization energy and electronegativity trends
  • Confusing moles and molarity (mol vs mol/L)

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