Bonding and Intermolecular Forces Flashcards
single bond
a bond formed from two electrons
how many electrons are involved in a double bond?
4
how many electrons are involved in a triple bond?
6
resonance hybrid
the “average” of possible resonance structures
bond dissociation energy (BDE)
the energy required to break a bond homolytically
homolytic bond cleavage
one electron of the bond being broken goes to each fragment of the molecule
heterolytic bond cleavage (dissociation)
both electrons of the electron pair that make up the bond end up the same atom
what does homolytic bond cleavage form?
radicals (has BDE)
what does heterolytic bond cleavage form?
ions
are the energies of heterolytic and homolytic bond breaking similar?
no, completely different energies
for similar bonds, the higher the bond order…
the shorter and stronger the bond
bond order
the number of bonds between adjacent atoms
comparisons of bond length and BDE should only be made for:
similar bonds
the greater the s-character in the hybrid orbitals:
the shorter the bond (s-orbitals are closer to the nucleus)
when comparing the same types of bonds, the longer the bond….
the weaker it is, the shorter the bond, the stronger it is
covalent bond
formed between atoms when each contributes one or more of its unpaired valence electrons so that the electrons are shared by both atoms to help complete both octets
polarity
when a molecule is partially negative on one end and partially positive on the other end
dipole moment
the polarity present in a polar molecule
what constitutes a polar bond?
if the electron density between the two nuclei is uneven
the greater the difference in electronegativity of the bonding atoms…
the more uneven the electron density and the greater the dipole moment
what constitutes a nonpolar bond?
the electron density between the two nuclei is even
coordinate covalent bond
when one atom donates both of the shared electrons in a bond
what are two other synonyms for Lewis base?
ligand or nucleophile
what’s another word for Lewis acid?
electrophile
what happens to the electrons in the breaking of a coordinate covalent bond?
the electrons that come from the ligand will leave with that ligand
ionic bond
cation and anions held together by electrostatic attraction
in ionic bonds, what is the strength of the bond proportional to?
the charges on the ions
in ionic bonds, what is the strength of the bond inversely proportional to?
the distance between ions, or the ionic radii
valence shell electron-pair repulsion theory (VSEPR)
since electrons repel one another, electron pairs, whether bonding or nonbonding, attempt to move as far apart as possible
molecular geometry
the shape of a molecule
how are sigma bonds formed?
formed by the end-to-end overlap of one hybridized orbital (or an s orbital in the case of hydrogen) from each of the two atoms participating in the bond
sigma bond
consists of two electrons that are localized between two nuclei
how are pi bonds formed?
formed by the proper, parallel, side-to-side alignment of two unhybridized p orbitals on adjacent atoms
pi bond
composed of two electrons that are localized to the region that lies on opposite sides of the plane formed by the two bonded nuclei and immediately adjacent atoms, not directly between the two nuclei
intermolecular forces
the relatively weak interactions that take place between neutral molecules
ion-dipole forces
polar molecules are attracted to ions
dipole-dipole forces
attraction between the positive end of one polar molecule and the negative end of another polar molecule
what is the strongest dipole-dipole force?
hydrogen-bonding
dipole-induced dipole force
a permanent dipole in one molecule induces a momentary dipole in a neighbouring nonpolar molecule
London dispersion forces
an instantaneous dipole in a nonpolar molecule may induce a dipole in a neighbouring nonpolar molecule: weak and transient interaction
how could LDF forces increase?
if size of molecule and its number of electrons increases-this increases partial charge of induced dipole
van der Waals forces
collectively refers to dipole forces, hydrogen bonding, and London forces
what is required for hydrogen bonding to occur?
1) a molecule must have a covalent bond between H and either N, O, or F
2) a molecule must have a lone pair of electrons on an N, O, or F atom
vapour pressure
the pressure exerted by the gaseous phase of a liquid that evaporated from the exposed surface of the liquid
what is the relationship between a substance’s intermolecular forces and vapour pressure?
weaker intermolecular forces=higher vapour pressure, more easily evaporated
volatile
easily vaporized liquids
aside from intermolecular forces, what influences vapour pressure?
temperature: increased temperature of substance=increased vapour pressure
ionic solid
held together by the electrostatic attraction between cations and anions in a lattice structure; the bonds that hold all the ions together in the crystal lattice are the same as the bonds that hold each pair of ions together
network solid
atoms are connected in a lattice of covalent bonds (all interactions between atoms are covalent bonds); the intermolecular forces are identical to the intramolecular forces
metallic solids
a covalently bound lattice of nuclei and their inner shell electrons surrounded by a “sea” of electrons
conduction electrons
freely roaming valence electrons in metallic solids that are not bound to any particular atom and is free to move throughout the lattice, allows for excellent conduction of electricity and heat
molecular solids
the particles at the lattice points of a crystal of a molecular solid are molecules held together by one of the three types of intermolecular interactions (H bond, dipole, LDF)
