CSET Science: Chemistry cheat sheet

Chemistry Content Domain

• Atomic number Z = protons; mass number A = protons + neutrons; isotopes differ in neutrons only, so they share chemical behavior but differ in mass and nuclear stability.

• Electron configuration follows Aufbau (lowest energy first), Pauli (max two electrons per orbital, opposite spins), and Hund's rule (maximize unpaired spins within a subshell); Cr and Cu are exceptions with half-filled/fully filled d subshells.

• Periodic trends: atomic radius decreases left-to-right across a period and increases down a group; ionization energy and electronegativity increase across a period and decrease down a group; electron affinity follows the same general direction as ionization energy.

• Bond type follows electronegativity difference: <0.4 nonpolar covalent, 0.4-1.7 polar covalent, >1.7 largely ionic; metallic bonding arises from delocalized valence electrons in a lattice.

• VSEPR electron-domain geometry: 2 linear, 3 trigonal planar, 4 tetrahedral, 5 trigonal bipyramidal, 6 octahedral; lone pairs compress bond angles (e.g., water ~104.5 degrees vs methane 109.5 degrees).

• Mole relationships: 1 mol = 6.022e23 particles = molar mass in grams; molarity M = mol solute / L solution; dilution M1V1 = M2V2; percent yield = actual/theoretical x 100.

• Stoichiometry uses mole ratios from the balanced equation; identify the limiting reactant by dividing each reactant's moles by its coefficient, and the smallest quotient limits the reaction.

• Gas laws: PV = nRT with R = 0.08206 L atm/(mol K) or 8.314 J/(mol K); combined gas law P1V1/T1 = P2V2/T2; STP (0 C, 1 atm) gives 22.4 L/mol for an ideal gas.

• Solution and colligative behavior: like dissolves like; electrolytes dissociate into ions; boiling point elevation and freezing point depression scale with total particle molality (van't Hoff factor i).