Key Concepts in Chemistry: Reactions, Bonds, and Theories

VSEPR Theory

Valence Shell Electron Pair Repulsion theory is used to predict the shape of molecules based on repulsion between electron pairs.

Key Shapes of VSEPR

Linear: 2 bonding pairs, 0 lone pairs (e.g., CO2); Trigonal Planar: 3 bonding pairs, 0 lone pairs; Tetrahedral: 4 bonding pairs; Trigonal Pyramidal: 3 bonding pairs, 1 lone pair (e.g., NH3); Bent: 2 bonding, 1 or 2 lone pairs (e.g., H2O).

Signs of a Chemical Reaction

Color change, temperature change, gas production, formation of a precipitate.

Types of Chemical Reactions

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.

Aufbau Principle

Electrons fill the lowest energy orbitals first.

Hund's Rule

Electrons fill degenerate orbitals singly before pairing.

Pauli Exclusion Principle

No two electrons can have the same set of 4 quantum numbers.

Heat Flow

Heat flows from high temperature to low temperature.

Endothermic Reaction

Absorbs heat (melting, boiling).

Exothermic Reaction

Releases heat (freezing, condensation).

Stoichiometric Mole Ratios

Ratios from balanced equations used to convert between moles of reactants/products.

Dalton's Atomic Theory

All matter is made of atoms; Atoms are indivisible (historical); Atoms of a given element are identical; Atoms combine in whole-number ratios.

Electron Configuration Order

1s, 2s, 2p, 3s, 3p, 4s, 3d...

Electron Capacity of Orbitals

s orbital: 2 e-; p orbital: 6 e-; d orbital: 10 e-.

Example of Electron Configuration

Fluorine = 1s2 2s2 2p5.

Limiting Reactant

The reactant that gets used up first and limits the amount of product formed.

Ionic Bonding

Transfer of electrons between metal and nonmetal, producing cations and anions.

Proton

Positive, nucleus.

Neutron

Neutral, nucleus.

Electron

Negative, orbitals.

Metallic Bonding

Bonding between metal atoms with delocalized electrons ('sea of electrons').

Valence Electrons

Electrons in the outermost shell that determine reactivity.

Resonance

Occurs when multiple valid Lewis structures exist for a molecule.

Bohr Model

Electrons move in fixed circular orbits around nucleus.

Wavelength vs Frequency

λ = wavelength, ν = frequency; Related by c = λν, where c is speed of light.

Covalent Bonds

Sharing of electrons between two nonmetals.

Lewis Structure

Diagram showing bonding between atoms and lone pairs of electrons. Shows how valence electrons are arranged. Used to determine molecule shape and resonance.

Atomic Structure

Consists of protons, neutrons, and electrons. Nucleus = dense center with p+ and n0. Electrons occupy defined energy levels around nucleus.

Intermolecular Forces

London Dispersion < Dipole-Dipole < Hydrogen Bonding. Affect boiling points, solubility, and state of matter.

Titration

Lab method to determine unknown concentration via neutralization. Uses an indicator to find equivalence point.

Bronsted-Lowry Theory

Acids = H+ donors. Bases = H+ acceptors.

Kinetic Molecular Theory (KMT)

Gases in constant, random motion. Collisions are elastic. Explains pressure, temperature, and volume relationships.

Solids

Definite shape and volume. Particles tightly packed. Crystalline vs. Amorphous solids.

STP (Standard Temperature and Pressure)

0°C (273 K) and 1 atm pressure. 1 mol gas = 22.4 L at STP.

Alloys

Mixtures of two or more metals. Example: bronze = copper + tin. Often stronger and more durable.

Ideal vs Real Gases

Ideal = no attraction/volume; real = slight attractions/volume. Real gases behave ideally at high temp, low pressure.

Rate of Solvation

Factors: temperature, agitation, particle size. Affects how fast a solute dissolves in a solvent.

Amphoterism

Ability to act as acid or base (e.g., H2O, HCO3-). Amphoteric substances respond to environment pH.

Saturated Solutions

Contain max solute at given temp. Any added solute won't dissolve.

Unsaturated Solutions

Can dissolve more solute at that temp.

Supersaturated Solutions

Contain more solute than stable; crystallizes easily. Formed by dissolving solute at high temp and slowly cooling.

Colligative Properties

Depend on number of particles. Include: Boiling point elevation, Freezing point depression, Vapor pressure lowering. Example: Salt lowers freezing point of water.

Gas Laws

Boyle's Law: P1V1 = P2V2 (inverse). Charles's Law: V1/T1 = V2/T2 (direct). Avogadro's Law: V ∝ n (direct).

Arrhenius Definition

Acid: Increases [H+]. Base: Increases [OH-].

Heating Curve

Shows temperature changes during phase changes. Flat regions = phase change (melting, boiling). Sloped = temperature change within a phase.

Percent Solution (% sol'n)

% by mass = (mass solute / mass solution) × 100. % by volume = (volume solute / volume solution) × 100. Used for expressing concentration in everyday terms.