Chemistry Key Terms: Formulas, Reactions, and Solutions

Chemical Formula

A representation showing the types and numbers of atoms in a compound.

Mole

A counting unit equal to 6.022 × 10^23 particles.

Avogadro's Number

6.022 × 10^23 particles per mole.

Molar Mass

The mass of 1 mole of a substance in g/mol.

Molar Volume

22.4 L/mol at STP.

Mass Percent Composition

(percent by mass) = (mass of element / total mass of compound) × 100

Empirical Formula

The simplest whole number ratio of elements in a compound.

Molecular Formula

The actual number of atoms of each element in a molecule.

Diatomic Elements

H2, N2, O2, F2, Cl2, Br2, I2

Solution

A homogeneous mixture of solute dissolved in solvent.

Solvent

The substance doing the dissolving.

Solute

The substance being dissolved.

Soluble

Capable of dissolving in a solvent.

Insoluble

Unable to dissolve in a solvent.

Aqueous Solution

A solution where water is the solvent.

Dissociation

Breaking apart into ions when dissolved in water.

Electrolyte

A substance that conducts electricity in solution by producing ions.

Nonelectrolyte

A substance that does not conduct electricity in solution.

Solubility

The amount of solute that dissolves in a given solvent.

Saturated Solution

A solution containing the maximum dissolved solute.

Unsaturated Solution

A solution that can dissolve more solute.

Supersaturated Solution

A solution containing more dissolved solute than normally possible.

Precipitation

The formation of an insoluble solid from solution.

Concentrated Solution

A solution with relatively large amount of solute.

Dilute Solution

A solution with relatively small amount of solute.

Molarity

M = moles solute / liters solution

Dilution Formula

M1V1 = M2V2

Chemical Reaction

Process where substances change into new substances.

Evidence of Chemical Reaction

Color change, gas formation, precipitate, temperature change, odor/light change.

Reactants

Starting substances in a reaction.

Products

Ending substances formed in a reaction.

Balanced Equation

Equation with equal atoms on both sides.

Precipitation Reaction

A reaction that forms an insoluble solid.

Molecular Equation

Shows compounds as complete formulas.

Complete Ionic Equation

Shows dissolved ionic compounds as ions.

Net Ionic Equation

Shows only species that actually react.

Spectator Ion

Ions unchanged during a reaction.

Acid-Base Reaction

Reaction between acid and base producing water and salt.

Redox Reaction

A reaction involving transfer of electrons.

Oxidation

Loss of electrons.

Reduction

Gain of electrons.

Combustion Reaction

Reaction with oxygen producing CO2 and H2O (for hydrocarbons).

Synthesis Reaction

Two or more substances combine into one product.

Decomposition Reaction

One compound breaks into simpler substances.

Single Displacement

One element replaces another in a compound.

Double Displacement

Exchange of ions between compounds.

Activity Series

Ranking of metals by reactivity.

Stoichiometry

Calculations based on balanced chemical equations.

Mole Ratio

Ratio from coefficients in balanced equation.

Limiting Reactant

Reactant used up first, limiting product amount.

Excess Reactant

Reactant left over after reaction.

Theoretical Yield

Maximum possible product amount.

Percent Yield

(actual yield / theoretical yield) × 100

Enthalpy

Heat energy change in a reaction.

Exothermic

Releases heat; ΔH is negative.

Endothermic

Absorbs heat; ΔH is positive.

Lewis Model

Model showing valence electrons as dots.

Lewis Structure

Diagram showing bonding and lone pairs.

Ionic Bond

Electron transfer between metal and nonmetal.

Covalent Bond

Sharing electrons between nonmetals.

Octet Rule

Atoms tend to gain 8 valence electrons.

Octet Exceptions

Incomplete octet, expanded octet, odd electron molecules.

Single Bond

1 shared pair of electrons.

Double Bond

2 shared pairs of electrons.

Triple Bond

3 shared pairs of electrons.

HONC Rule

H forms 1 bond, O 2, N 3, C 4.

Polyatomic Ion

A charged group of covalently bonded atoms.

Resonance

Multiple valid Lewis structures.

VSEPR Theory

Electron pairs repel to maximize distance.

Electron Geometry

Arrangement of electron groups.

Molecular Geometry

Arrangement of atoms only.

Linear

180° bond angle.

Trigonal Planar

120° bond angle.

Tetrahedral

109.5° bond angle.

Sigma Bond

First bond formed by direct overlap.

Pi Bond

Additional bond from sideways overlap.

Hybridization

Mixing orbitals to form new bonding orbitals.

sp

2 electron groups, linear.

sp2

3 electron groups, trigonal planar.

sp3

4 electron groups, tetrahedral.

Electronegativity

Ability of atom to attract electrons.

Nonpolar Covalent

Equal sharing of electrons.

Polar Covalent

Unequal sharing of electrons.

Ionic Bonding

Transfer of electrons due to large EN difference.

Polar Molecule

Molecule with uneven charge distribution.

Kinetic Molecular Theory

Gas particles are tiny, move randomly, elastic collisions, negligible volume, no IMFs.

Pressure

Force exerted per unit area.

Atmospheric Pressure

Pressure from Earth's atmosphere.

Barometer

Instrument measuring atmospheric pressure.

STP

1 atm and 273 K (0°C).

Boyle's Law

P1V1 = P2V2

Charles's Law

V1/T1 = V2/T2

Gay-Lussac's Law

P1/T1 = P2/T2

Combined Gas Law

P1V1/T1 = P2V2/T2

Avogadro's Law

V1/n1 = V2/n2

Ideal Gas Law

PV = nRT

Dalton's Law

Ptotal = P1 + P2 + P3...

Graham's Law

Lighter gases effuse faster.

Diffusion

Movement of particles from high to low concentration.

Effusion

Gas escaping through tiny opening.