Chem #3 Exam

a chemical bond formed by the electrostatic attraction between positive and negative ions

Involves the transfer of one or more electrons from the valence shell of one atom to the valence shell of another

Especially prevalent in compounds formed between Group 1A and 2A elements with Group 6A and 7A elements

the energy required to completely separate one mole of a solid ionic compound inot gaseous ions

• They can be calculated from Coulomb's law or measured indirectly by the Born-Haber cycle
• **cannot be measured directly**

Allows the indirected determination of the lattice energy of an ionic solid

a chemical bond formed by the sharing of a pair of electrons between atoms

• Single Bond: a single pair of electrons is shared by two atoms
• Double Bond: two pairs of electrons are shared by two atoms (often C, N, O and S)
• Triple Bond: three pairs of electrons are shared by two atoms (often C and N)

The distance between the nuclei of two covalent atoms in a molecule

the attractive forces that holds the atoms together within a molecule

• the forces that operate between molecules
• *relatively weak in covalent compounds
• **very strong in ionic compounds

a covalent bond in which the bonding electrons spend more time near one atom that the other

• Pure covalent bond: neutral atoms held together by equally shared electrons
• Polar covalent bond: partially charged atoms held toegher by unequally shared electrons
• Pure ionic bond: oppositely charged ions held together by electrostatic attraction

a measure of the ability of an atom in a molecule to draw bonding electrons to itself

• came up with the Mulliken scale which calculates average ionization potential and electron affinity.
• (no longer use the Mulliken scale)

• Created the Pauling Scale - derived from bond energies and is very widely used.
• 
• X increases left to right, decreases top to bottom

• F : 4.0
• O : 3.5
• N~Cl : 3.0
• Br : 2.8

• Electron Affinity: how much an isolated atom wants someone else's electrons
• Electronegativity: how much an atom wants the shared electrons in a chemical bond

Polarity of a bond depends upon the difference in electronegativity of the two bonded atoms

• -if Delta X is < 0.5 the bond is purely covalent (nonpolar)
• -if 0.5 is < Delta X and < 2.0 the bond is polar covalent
• -if Delta X is greater than or equal to 2.0 the bond is ionic

the hypothetical charge of an atom

all possible Lewis Structures for a single molecule that cannot be represented accurately by only one Lewis structure

a type of bonding in which a pair of bonding electrons is spread over a number of atoms rather than localized between two

• -molecules having an odd number of electrons
• -molecules with an atom from Group IIA or IIIA having < 8 valence electrons around that atom
• -molecules with an atom having unfilled nd orbitals may have > 8 valence electrons around that atom

the enthalpy charge Delta H required to break a particular bond in one mole of gaseous molecules

the average enthalpy change for the breaking of an A-B bond in the gas phase

• the number of pairs of electrons in a bond
• Trends:
• -Bond enthalpy- increases with bond order
• -Bond length- decreases with bond order

the three-dimensional arrangements of atoms in a molecule

*Importance: a molecule's geometry affects its physical and chemical properties

-Predicts the shape of molecules and ions

Basis: Valence-shell electron-pairs (bonding and nonbonding) are kept as far away from one another as possible

- a lone pair of electrons or a chemical bond

**Note: Double and Triple bonds are treated like Single bonds and count as one electron domain

• Arrangement of electron domains: determined by total number of electron domains (i.e., # of bonds AND non-bonding pairs)
• Molecular geometry: determined by number of bonds