Pharm-D Admission Test Chemistry Syllabus

Define electronegativity and identify the most electronegative element.

Electronegativity is the tendency of an atom to attract a shared (bonding) pair of electrons toward itself. Fluorine is the most electronegative element.

What is the difference between an ionic bond and a covalent bond?

An ionic bond forms by complete transfer of electrons between atoms (creating cations and anions held by electrostatic attraction); a covalent bond forms by sharing of electron pairs between atoms.

State the octet rule in chemical bonding.

Atoms tend to gain, lose, or share electrons to achieve a stable noble-gas configuration of eight electrons in their outermost shell.

What conditions favor the formation of an ionic bond?

Low ionization energy of the metal, high electron affinity of the non-metal, high lattice energy, and a large electronegativity difference (typically > 1.7) between the atoms.

Distinguish between a sigma bond and a pi bond.

A sigma bond forms by head-on (axial) overlap of orbitals and is stronger; a pi bond forms by sideways (lateral) overlap of p-orbitals and is weaker. Single bonds are sigma; double/triple bonds contain one sigma plus pi bond(s).

What is a coordinate (dative) covalent bond? Give an example.

A covalent bond in which both shared electrons are donated by one atom. Example: the bond between N and H in the ammonium ion NH4+ (or H3N -> BF3).

What is hybridization?

The intermixing of atomic orbitals of slightly different energy to form an equal number of new, equivalent hybrid orbitals with definite directional geometry.

What is the hybridization, geometry, and bond angle of a molecule like methane (CH4)?

sp3 hybridization, tetrahedral geometry, bond angle 109.5 degrees.

What is the hybridization, geometry, and bond angle of a molecule like BF3 or ethene's carbon?

sp2 hybridization, trigonal planar geometry, bond angle 120 degrees.

What is the hybridization, geometry, and bond angle of a molecule like BeCl2 or ethyne's carbon?

sp hybridization, linear geometry, bond angle 180 degrees.

Why is the bond angle in water (104.5 degrees) and ammonia (107 degrees) less than the ideal tetrahedral angle of 109.5 degrees?

Lone pairs on the central atom exert greater repulsion than bonding pairs, compressing the bond angle. Water has two lone pairs and ammonia has one.

What is hydrogen bonding, and between which atoms does it occur?

A relatively strong dipole-dipole attraction between a hydrogen atom bonded to a highly electronegative atom (F, O, or N) and a lone pair on another electronegative atom (F, O, or N).

Why does water have an unusually high boiling point compared to H2S?

Water molecules form extensive intermolecular hydrogen bonds (O-H...O), which require extra energy to break; H2S has only weak dipole-dipole/London forces.

List the intermolecular (van der Waals) forces in increasing order of strength.

London (dispersion) forces < dipole-dipole forces < hydrogen bonding (hydrogen bonding is the strongest of these).

What are London dispersion forces and which type of molecules show them most strongly?

Weak attractive forces arising from temporary/instantaneous dipoles due to fluctuating electron clouds; they are present in all molecules and are strongest in large, easily polarizable (high molecular mass) molecules.

Define bond energy.

The average amount of energy required to break one mole of a particular bond in the gaseous state, or the energy released when that bond forms; it indicates bond strength.

How does bond energy relate to bond order and bond length?

Higher bond order means greater bond energy and shorter bond length; e.g., triple bonds are stronger and shorter than double bonds, which are stronger and shorter than single bonds.

What makes a covalent bond polar, and what is a dipole moment?

A bond is polar when the bonded atoms differ in electronegativity, causing unequal sharing of electrons. The dipole moment (mu = q x d) measures bond polarity in debye units.

Why is CO2 nonpolar despite having two polar C=O bonds?

CO2 is linear and symmetrical, so the two equal bond dipoles point in opposite directions and cancel, giving a net dipole moment of zero.

State the ideal gas equation and define each term.

PV = nRT, where P = pressure, V = volume, n = number of moles, R = universal gas constant (0.0821 L atm K^-1 mol^-1 or 8.314 J K^-1 mol^-1), and T = absolute temperature.

State Boyle's law and Charles's law.

Boyle's law: at constant T and n, V is inversely proportional to P (PV = constant). Charles's law: at constant P and n, V is directly proportional to absolute T (V/T = constant).

State Avogadro's law and Dalton's law of partial pressures.

Avogadro's law: at constant T and P, equal volumes of gases contain equal numbers of molecules. Dalton's law: total pressure of a gas mixture equals the sum of the partial pressures of its components (P_total = P1 + P2 + ...).

Under what conditions do real gases deviate most from ideal behavior, and why?

At high pressure and low temperature, because under these conditions intermolecular forces become significant and the molecular volume is no longer negligible compared to the container volume.

Define vapor pressure of a liquid and state how it changes with temperature.

Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid at a given temperature; it increases as temperature increases.

Define the boiling point of a liquid in terms of vapor pressure.

The boiling point is the temperature at which the vapor pressure of the liquid becomes equal to the external (atmospheric) pressure.

What is the difference between evaporation and boiling?

Evaporation is a surface phenomenon occurring at any temperature below the boiling point; boiling occurs throughout the bulk of the liquid at a specific temperature where vapor pressure equals external pressure.

Distinguish between crystalline and amorphous solids.

Crystalline solids have a regular, repeating long-range ordered arrangement of particles, sharp melting points, and are anisotropic; amorphous solids have irregular short-range order, melt over a range, and are isotropic.

Define a unit cell and a crystal lattice.

A crystal lattice is the regular three-dimensional arrangement of points (particles) in space; a unit cell is the smallest repeating unit that, when repeated, generates the entire crystal lattice.

How many atoms per unit cell are in simple cubic, body-centered cubic (BCC), and face-centered cubic (FCC) lattices?

Simple cubic: 1 atom; BCC: 2 atoms; FCC: 4 atoms per unit cell.

Define enthalpy (H) and enthalpy change of reaction (delta H).

Enthalpy is the total heat content of a system at constant pressure (H = U + PV). Delta H is the heat absorbed or released during a reaction at constant pressure (delta H = H_products - H_reactants).

What is the difference between an exothermic and an endothermic reaction in terms of delta H?

Exothermic reactions release heat and have a negative delta H (delta H < 0); endothermic reactions absorb heat and have a positive delta H (delta H > 0).

State Hess's law of constant heat summation.

The total enthalpy change of a reaction is the same whether it occurs in one step or several steps, depending only on the initial and final states, not the path taken.

State the first law of thermodynamics and its mathematical expression.

Energy can neither be created nor destroyed, only converted from one form to another. Mathematically: delta U = q + w, where delta U is change in internal energy, q is heat added to the system, and w is work done on the system.

Define internal energy (U) of a system.

Internal energy is the total of all kinetic and potential energies of the particles in a system; its absolute value cannot be measured, only the change (delta U) is determined.

State the law of mass action.

At constant temperature, the rate of a chemical reaction is directly proportional to the product of the molar concentrations of the reactants, each raised to a power equal to its coefficient in the balanced equation.

For the reaction aA + bB <-> cC + dD, write the equilibrium constant expression Kc.

Kc = ([C]^c [D]^d) / ([A]^a [B]^b), where the brackets denote equilibrium molar concentrations.

State Le Chatelier's principle.

If a system at equilibrium is subjected to a change in concentration, temperature, or pressure, the equilibrium shifts in the direction that tends to counteract (relieve) the imposed change.

According to Le Chatelier's principle, how does increasing pressure affect a gaseous equilibrium?

Increasing pressure shifts the equilibrium toward the side with fewer moles of gas; if both sides have equal moles of gas, pressure has no effect on the position of equilibrium.

How does increasing temperature affect the equilibrium of an exothermic reaction?

For an exothermic reaction (heat is a product), increasing temperature shifts the equilibrium backward (toward reactants), decreasing the value of Kc.

Why does a catalyst not change the position of equilibrium?

A catalyst speeds up the forward and reverse reactions equally, so it lets equilibrium be reached faster but does not change Kc or the equilibrium concentrations.

Define solubility product (Ksp) for a sparingly soluble salt.

Ksp is the equilibrium constant for the dissolution of a sparingly soluble ionic solid; it equals the product of the molar concentrations of its ions, each raised to the power of its stoichiometric coefficient, in a saturated solution.

Write the Ksp expression for a salt of type AB2 (e.g., CaF2) that dissociates into A2+ and 2B-.

For CaF2 <-> Ca2+ + 2F-, Ksp = [Ca2+][F-]^2. If solubility is s, then Ksp = (s)(2s)^2 = 4s^3.

How is the ionic product used to predict precipitation relative to Ksp?

If the ionic product > Ksp, precipitation occurs (solution is supersaturated); if ionic product = Ksp, the solution is just saturated; if ionic product < Ksp, no precipitate forms (unsaturated).

What is the common ion effect?

The suppression of the ionization (or solubility) of a weak electrolyte or sparingly soluble salt caused by adding a strong electrolyte that provides an ion common to the equilibrium, shifting it backward per Le Chatelier's principle.

Explain how the common ion effect decreases the solubility of AgCl when NaCl is added.

Added NaCl increases the Cl- concentration; to keep Ksp = [Ag+][Cl-] constant, the equilibrium AgCl <-> Ag+ + Cl- shifts left, precipitating AgCl and reducing its solubility.