Gen Chem 1 Chapter 7

Flashcards on Chemical Bonding and Molecular Structure

Lattice energy

The energy change occurring when separated gaseous ions are packed together to form an ionic solid.

Ionic Bond in NaCl

The strong electrostatic attraction between Na+ and Cl– ions that holds them tightly together in solid.

Dissociation of NaCl(s)

It requires 769 kJ of energy to dissociate one mole of solid NaCl into separate gaseous Na+ and Cl– ions

Trend in Lattice Energy: Ion Size

As we move down a column, the lattice energy is less negative (increases)

Trends in Lattice Energy: Ion Charge

Lattice energy becomes more negative (decreases) with increasing magnitude of ionic charge (similar radii).

Lattice Energy and Ionic Compound Stability

Greater charged ions as well as smaller sized ions lead to more negative lattice energy values and more stable ionic compounds.

Physical Properties of Ionic Compounds

Ionic compounds have high melting points and boiling points due to the strong attraction between cations and anions in a crystalline structure.

Bond Energy

The energy required to break 1 mole of a covalent bond in the gas phase.

Trends in Average Bond Energies

Bond energy and bond strength increase as the number of bonding electrons increases.

Trends in Average Bond Energies

Bond energy and bond strength increase as the bond becomes shorter.

Calculating DHrxn from Bond Energies

The golden rule: Bond breaking is endothermic, absorb energy (+), Bond forming is exothermic, releases energy, (−)

Bond Length

The distance between the nuclei of two bonded atoms.

Bond Lengths and Number of Electrons Shared

The more electrons two atoms share, the shorter the covalent bond and the stronger the bond.

VSEPR Theory

Each group of valence electrons around the central atom is located as far away as possible (maximize separation) from the others in order to minimize repulsion.

Electron Group

Any number of electrons that occupy a localized region around an atom (single bond, double bond, triple bond, lone pair, or lone electron).

Electron Geometry

The arrangement of electron groups in a molecule.

Molecular Geometry

The arrangement of atoms in a molecule.

The Effect of Lone Pairs

Lone pairs distort bond angles due to stronger repulsion compared to bonding pairs.

Polar molecules

Molecules with positive and negative ends (net dipole moment).

Nonpolar molecules

Molecules without positive and negative ends (no net dipole moment).

Conditions for Polarity

For a molecule to be polar, it must have at least one polar bond (0.5 ≤ ∆EN ≤ 1.7) and an asymmetrical shape that polar bonds do not cancel out.