Key Chemistry Concepts and Formulas

Posted on Mar 31, 2025 in Chemistry

Conversions

  • Celsius to Fahrenheit: F = (9/5) * C + 32
  • Celsius to Kelvin: K = C + 273

Atomic Structure

  • Atomic Mass: Protons + Neutrons (upper left symbol)
  • Atomic Number: Protons (bottom left symbol)

Constants

  • Planck’s Constant (h): 6.6260755 x 10-34 J*s

Photons

  • Energy of a Photon: E = hv or E = hc / wavelength

Electronic Transitions

  • Absorption: When energy is absorbed by the hydrogen atom, the electron is excited to a higher energy level or orbital.
  • Emission: When the electron relaxes from a higher energy orbital to a lower one, it emits a photon.

Filling Orbitals

  • s = 2, p = 6, d = 10, f = 14
  • 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f

Periodic Trends

  • Atomic Radius: Increases down a group and decreases across a row.
  • Ionization Energy: Amount of energy needed to remove 1 mole of e- from 1 mole of ground-state atoms or ions in the gas phase.
  • Electron Affinity: Energy change that occurs when 1 mole of electrons combine with 1 mole of atoms or ions in the gas phase.
  • Electronegativity: Increases moving up and across (upper right is highest).

Chemical Bonds

  • Ionic Bond: Chemical bond resulting from electrostatic attraction of a cation for an anion.
  • Covalent Bond: Bond resulting from a sharing of outermost electrons.
  • Metallic Bond: Chemical bond consisting of nuclei of metal atoms surrounded by a “sea” of shared e-.

Bond Types Comparison

IonicCovalentMetallic
Elements InvolvedMetal + NonmetalNonmetal(s) and/or Metalloid(s)Metals
Electron DistributionTransferredSharedPooled

Other Key Concepts

  • Lattice Energy: Amount of energy required to convert a mole of ionic solid to its constituent ions in the gas phase.
  • Polar Covalent Bond: Unequal sharing of bonding pair of e- between atoms.
  • Electronegativity Values: <0.5 is covalent/nonpolar, 0.5-2.0 is polar covalent, >2.0 is ionic.
  • Formal Charge: (# valence e-) – (# unshared e-) – (1/2)(# e- in bonding pairs)
  • Free Radicals: Molecules having an odd number of electrons.
  • Steric Number (SN): (# atoms bonded to central atom) + (# lone pairs on central atom)
  • SN2 = linear, SN3 = trigonal planar, SN4 = tetrahedral, SN5 = trigonal bipyramidal
  • Percent Composition: (mass of element in compound / mass of compound) * 100
  • Empirical Formula: Assume 100g sample, get moles using molar mass, then determine proportions.
  • Empirical to Molecular Formula: Look at molar mass of whole molecule and multiply to make it proportionally match that.
  • Limiting Reactant: Substance that is completely consumed in a reaction.
  • Percent Yield: (actual yield / theoretical yield) * 100

Solutions

  • Molarity (M): Moles of solute / Liter of solution (n/V)
  • Mass of Solute: Volume * Molarity * Molar Mass
  • Dissociation: An ionic compound upon dissolution breaks apart into its constituent ions.
  • Ionization: Process by which a molecular compound forms ions when it dissolves.
  • Nonelectrolytes: Substances in which no ionization occurs.

Acids and Bases

  • Acids: Proton donors, Bases: Proton acceptors
  • Neutralization: Reaction that takes place when an acid reacts with a base, producing a solution of a salt in water.

Redox Reactions

  • Oxidation: Reaction that increases oxygen content (loss of e-)
  • Reduction: Reaction involving loss of O2 (gain of e-)