Class Two Flashcards
how to calculate formal charge
FC = V - ½ B - L
what is bond length
the distance between 2 nuclei that are bonded to one another
what is bond dissociation energy
the energy required to break the bond homolytically (one electron of the bond being broken goes to each fragment of the molecule)
heterolytic bond cleavage aka dissociation
both electrons of the electron pair that make up the bond end up on the same atom → forms an anion and a cation
the higher the bond order..
the shorter and stronger the bond
the longer the bond..
the weaker it is
the shorter the bond..
the stronger it is
what is a covalent bond
formed between twos when each contributes one or more of its unpaired valence electrons
electrons are shared by both atoms to complete octets
when is a bond polar
when the electron density between two nuclei are uneven
when is a bond non polar
when the electron density between the two nuclei is even (little to no difference in electronegativity)
what is a coordinate covalent bond
when one atom donates both of the shared electrons in a bond
when an atom gives the electrons in a coordinate covalent bond, it acts as a..
lewis base (nucleophile)
a lewis base must have..
a pair of nonbonding electrons
what is an ionic bond
gaining/losing of electrons
held together by the electrostatic attraction between a cation and an anion
basis of VSEPR theory
electrons repel each other therefore they try to move as far apart as possible
what is a sigma bond
a bond with 2 electrons that are localized between 2 nuclei
what is a pi bond
composed of 2 electrons that are localized to the region that lies on opposite sides of the plane
if a molecule contains no polar bonds..
it cannot be polar
what are intermolecular forces
the relatively weak interactions that take place between neutral molecules
ion dipole forces
polar molecules attracted to ions
dipole dipole forces
attractions 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 inducing a dipole in a neighbour non polar molecule for a moment
London dispersion force
instantaneous dipole in a non polar molecule can induce a dipole in a neighbour non polar molecule
characteristics of London dispersion forces
very weak
substances with higher intermolecular forces have..
higher melting/boiling points, greater viscosities and low vapour pressures
what are van Der Waals forces
dipole forces, hydrogen bonding and London forces
criteria for a hydrogen bond to form
molecule have covalent bond between H and either N, O or F
another molecule must have a lone pair of electrons on an N, O or F atom
what is vapour pressure
the pressure exerted by the gaseous phase of a liquid that is exported from the exposed surface of the liquid
intermolecular forces and vapour pressure relationship
the weaker the intermolecular forces, the high its vapour pressure (easily evaporates)
volatile liwuids
easily vaporized liquids (high vapour pressures)
the vapour pressure of a substance is indirectly related to..
boiling point
what is an ionic solid
a solid held together by the electrostatic attraction between cations and anions in a lattice structure
what is a network solid
atoms are connected in a lattice of covalent bonds
intermolecular forces are identical to intramolecular forces (like an ionic solid)
very strong and hard solids at room temp (e.g. diamond)
what is a metallic solid
covalently bond lattice of nuclei and their inner shell electrons, surrounded by conduction electrons (free to move throughout the lattice)
why are metals good conductors of heat
due to their conduction electrons - free to move around
what is a molecular solid
held together by hydrogen bonds, dipole-dipole forces or London forces (intermolecular forces)
weaker → lower melting and boiling points
often liquids or gases
what is a chelate
ligand that donates multiple lone pairs
strongest intermolecular force
ion-dipole force
dipole induced dipole interactions occur between..
a polar and non polar molecule
which intermolecular force is seen with all molecules
London forces
what is thermodynamics
the transformation of energy from one from to another
zeroth law of thermodynamics
if two systems are both in thermal equilibrium with a third system, then the two initial systems are in thermal equilibrium with one another
thermal equilibrium and temperature
if two systems are in thermal equilibrium, they have the same temperature
first law of thermodynamics
the total energy of the universe is constant - energy cannot be created or destroyed
when energy flows into a system from the surroundings..
the energy of the system increase and the energy of the surroundings decreases
when energy flows out of a system into the surroundings..
the energy of the system decreases and the energy of the surroundings increase
what is enthalpy
measure of the heat energy that is released or absorbed when bonds are broken/formed during a reaction (constant P)
when a bond is formed..
energy is released → enthalpy is negative
enthalpy of a reaction =
Hproducts - Hreactants
another name for the enthalpy change of a reaction
heat of reaction
what are standard conditions
298 K (25 C)
pressure = 1 atm
solutions = conc of 1 M
what is the standard heat of formation
the amount of energy required to make one mole of a compound from its constituent elements in their natural form
standard heat of formation of elements in their natural form
zero
what does a positive standard heat of formation mean
input of heat is required to make that compound from its constituent elements
what does a negative standard heat of formation mean
making that compound from its elements gives off energy
Hess’s law of heat summation
if a reaction occurs in many steps, the sum of the energies absorbed/given off in all the steps will be the same for the overall reaction
Hess’s law: if a reaction is reversed..
the sign for enthalpy is reversed too
Hess’s law: if an equation is multiplied by a coefficient..
then the enthalpy must be multiplied by the same number
to break a bond..
3energy is needed
in making a bond..
energy is released
second law of thermodynamics
disorder of the universe increases in a spontaneous process
change of entropy equation =
Sproducts - Sreactants
if randomness increases, or order decreases..
then entropy is positive
if randomness decreases, or order increases
then entropy is negative
third law of thermodynamics
absolute zero = zero entropy
entropy of a pure substance at zero temperature = zero
Gibbs free energy
energy that’s available to do useful work from a chemical reaction
Gibbs free energy formula
change in G = change in H - (T)(change in S)
if G is less than O..
reaction is spontaneous in the forward direction
if G = 0..
reaction is at equilibrium
if G is greater than 0..
the reaction is non spontaneous in the forward direction
