Principles of Chemistry I: Bond Strength and Molecular Structure

Bond Energy

Energy needed to break one mole of bonds.

Enthalpy (H)

Measurement of energy in a thermodynamic system.

Endothermic Process

Absorbs heat from surroundings during reaction.

Exothermic Reaction

Releases heat; ΔH is negative.

Lattice Energy (ΔH lattice)

Energy to separate one mole of ionic solid.

Born-Haber Cycle

Series of steps to form ionic solids.

Ionization Energy (IE)

Energy required to remove an electron from an atom.

Electron Affinity (EA)

Energy change when an electron is added to an atom.

Bond Dissociation Energy (D)

Energy needed to break a bond in a molecule.

Covalent Bond

Chemical bond formed by sharing electron pairs.

Single Bond

One pair of shared electrons between atoms.

Double Bond

Two pairs of shared electrons between atoms.

Triple Bond

Three pairs of shared electrons between atoms.

VSEPR Theory

Predicts molecular structure based on electron repulsion.

Bond Length

Distance between the nuclei of two bonded atoms.

Bond Angle

Angle between two bonds including a common atom.

Molecular Polarity

Distribution of electrical charge across a molecule.

Regions of Electron Density

Includes lone pairs and bonding pairs around atoms.

Repulsion Order

Lone pair-lone pair > lone pair-bonding > bonding-bonding.

Terminal Atom Locations

Positions of atoms in linear and planar geometries.

Trigonal Bipyramidal Geometry

Five regions of electron density around a central atom.

Octahedral Geometry

Six regions of electron density around a central atom.

Lewis Structure

Diagram showing bonds and lone pairs in a molecule.

Average Bond Energy

Mean energy required to break bonds in a molecule.

ΔH for Reactions

Sum of bond energies broken minus formed.

Molecular Structure Prediction

Determining shape based on electron pair arrangements.

Bond Strength

Energy required to break a bond; stronger bonds require more energy.

Crystal Type Constant (C)

Constant in lattice energy formula based on crystal structure.

Interionic Distance (Ro)

Distance between ions in a crystal lattice.

CO2

2 regions of electron density

BCl3

3 regions of electron density

H2O

4 regions of electron density

Electron-pair geometry for CO2

linear

Electron-pair geometry for BCl3

trigonal planar

Electron-pair geometry for H2O

tetrahedral

Number of Lone Pairs for CO2

4

Number of Lone Pairs for BCl3

0

Number of Lone Pairs for H2O

2

Molecular Structure for CO2

linear

Molecular Structure for BCl3

trigonal planar

Molecular Structure for H2O

Bent

Regions of electron density for N

4

Regions of electron density for CH2

4

Regions of electron density for CO2 (in multicenter molecules)

3

Regions of electron density for OH

4

Electron-pair geometry for N

Tetrahedral

Electron-pair geometry for CH2

Tetrahedral

Electron-pair geometry for CO2 (in multicenter molecules)

Trigonal Planar

Electron-pair geometry for OH

linear

Number of Lone Pairs for N2

2

Number of Lone Pairs for CH2

0

Number of Lone Pairs for CO2 (in multicenter molecules)

0

Number of Lone Pairs for OH

2

Molecular Structure for N2

linear

Molecular Structure for CH2

Tetrahedral

Molecular Structure for CO2 (in multicenter molecules)

Trigonal Planar

Molecular Structure for OH

Bent

Bond dipole moment formula

µ= bond dipole moment; Q= magnitude of the partial charges; r: distance between charges

Definition of a Polar molecule

A molecule with a separation of charge, depending on its molecular structure and the polarity of each of its bonds.

Definition of a Nonpolar molecule

A molecule without a separation of charge.

Dipole moment

Measures the extent of net charge separation in the molecule as a whole.

Avogadro's Number

6.02214179 × 10^23.

Definition of a mole

The amount of a substance containing the same number of discrete entities as the number of atoms in a sample of pure carbon-12 weighing exactly 12 g.

Molar mass

The mass in grams of 1 mole of that substance, expressed in units of grams per mole (g/mol).

Saccharin

Artificial sweetener with formula C7H5NO3S.

Molar Mass

Mass of one mole of a substance, measured in g/mol.

Percent Composition

Percentage by mass of each element in a compound.

Empirical Formula

Simplest whole-number ratio of elements in a compound.

Molecular Formula

Actual number of atoms of each element in a compound.

Molarity (M)

Moles of solute per liter of solution.

Dilution

Process of reducing solution concentration by adding solvent.

Solvent

Component of solution present in greater concentration.

Solute

Component of solution present in lower concentration.

Aqueous Solution

Solution where water is the solvent.

Concentration

Relative amount of a component in a solution.

Mass Percentage

Mass of component divided by total mass, expressed as %.

Volume Percentage

Volume of solute divided by total volume, expressed as %.

Mass-Volume Percentage

Ratio of solute mass to solution volume, expressed as %.

Parts per Million (ppm)

Mass of solute per million parts of solution.

Parts per Billion (ppb)

Mass of solute per billion parts of solution.

Molecular Mass

Mass of one molecule, measured in amu.

Formula Mass

Sum of atomic masses in a chemical formula.

Stoichiometry

Calculation of reactants and products in chemical reactions.

Gas Composition

Percentage of different gases in a mixture.

Concentration Units

Various ways to express solution concentration.

Dilution Equation

n1 = n2; relates concentrations before and after dilution.

Hydrochloric Acid

Aqueous solution of HCl, commonly used in labs.

Physiological Saline

0.9% (m/v) NaCl solution for medical use.

Ethanol Production

Bacterial fermentation process producing ethanol and gas.

Chemical Reagents

Substances used in chemical reactions for analysis.

Chemical Analysis

Determining the composition of substances.

Concentration Calculation

Computing concentration based on mass and volume.