Essential Chemistry Formulas and Concepts

Temperature 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)

Quantum Mechanics

• Planck's Constant (h): 6.6260755 x 10^-34 J*s
• Energy of a Photon: E = hv or E = hc / wavelength

Electronic Transitions

• Absorption: When energy is absorbed by an atom, an electron is excited to a higher energy level or orbital.
• Emission: When an 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 electrons 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.

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 electrons.

Bond Types Comparison

Lattice Energy

Amount of energy required to convert a mole of ionic solid to its constituent ions in the gas phase.

Electronegativity

Increases moving up and across the periodic table (upper right is highest).

Polar Covalent Bonds

Unequal sharing of bonding pair of electrons between atoms.

Electronegativity values: <0.5 is covalent/nonpolar, 0.5-2.0 is polar covalent, >2.0 is ionic.

Formal Charge

(# valence electrons) - (# unshared electrons) - 1/2 (# electrons 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, determine proportions.

Empirical to Molecular Formula

Look at molar mass of whole molecule and multiply to proportionally match that.

Limiting Reactant

Substance that is completely consumed in a reaction.

Percent Yield

(Actual yield / Theoretical yield) * 100

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 are proton donors, bases are 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 electrons).
• Reduction: Reaction involving loss of O₂ (gain of electrons).