ECAT Chemistry Syllabus

State the Aufbau principle.

Electrons fill orbitals in order of increasing energy, lowest energy orbitals first.

What is the electronic configuration of chromium (Z = 24), and why is it anomalous?

[Ar] 3d^5 4s^1; the half-filled 3d subshell gives extra stability, so one 4s electron shifts to 3d.

What is the electronic configuration of copper (Z = 29)?

[Ar] 3d^10 4s^1; a fully filled 3d subshell provides extra stability.

What is the maximum number of electrons in a shell with principal quantum number n?

2n^2 electrons.

How many orbitals and electrons can the p, d, and f subshells hold?

p: 3 orbitals (6 electrons); d: 5 orbitals (10 electrons); f: 7 orbitals (14 electrons).

What is the shape of an s orbital and a p orbital?

s orbital is spherical; p orbital is dumbbell-shaped.

What is an atomic spectrum, and what type does hydrogen produce?

An atomic spectrum is the pattern of wavelengths emitted or absorbed by atoms; hydrogen produces a line (discontinuous) emission spectrum.

Name the spectral series of hydrogen in the visible region and the region of the Lyman series.

The Balmer series lies in the visible region (n -> 2); the Lyman series lies in the ultraviolet region (n -> 1).

State the postulates of the kinetic molecular theory of gases (key points).

Gas particles are in constant random motion, have negligible volume, exert no intermolecular forces, undergo elastic collisions, and their average kinetic energy is proportional to absolute temperature.

State Boyle's law and its equation.

At constant temperature, the volume of a fixed mass of gas is inversely proportional to its pressure: PV = constant (P1V1 = P2V2).

State Charles's law and its equation.

At constant pressure, the volume of a fixed mass of gas is directly proportional to its absolute temperature: V/T = constant (V1/T1 = V2/T2).

State the ideal gas equation and identify each term.

PV = nRT, where P = pressure, V = volume, n = moles, R = gas constant (0.0821 dm^3 atm/mol K), T = absolute temperature.

State Avogadro's law.

Equal volumes of all gases at the same temperature and pressure contain an equal number of molecules.

State Dalton's law of partial pressures.

The total pressure of a mixture of non-reacting gases equals the sum of the partial pressures of the individual gases: P_total = P1 + P2 + P3...

State Graham's law of diffusion.

At constant temperature and pressure, the rate of diffusion of a gas is inversely proportional to the square root of its density (or molar mass): rate proportional to 1/sqrt(M).

Why do real gases deviate from ideal behavior, and under what conditions?

Real gases deviate due to finite molecular volume and intermolecular attractions; deviations are greatest at high pressure and low temperature.

List the main types of intermolecular forces in order of increasing strength.

London dispersion forces < dipole-dipole forces < hydrogen bonding (all weaker than ionic/covalent bonds).

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

A 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.

Define vapor pressure and its relationship with temperature.

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

Define boiling point of a liquid.

The temperature at which the vapor pressure of a liquid equals the external (atmospheric) pressure.

What is surface tension, and how does it change with temperature?

Surface tension is the force acting along the surface of a liquid that minimizes surface area; it decreases as temperature increases.

Distinguish between crystalline and amorphous solids.

Crystalline solids have a regular, ordered, repeating arrangement of particles and sharp melting points; amorphous solids have a disordered arrangement and melt over a range of temperatures.

Name the four main types of crystalline solids and one example of each.

Ionic (NaCl), covalent/network (diamond), metallic (Cu), and molecular (ice).

What is a unit cell?

The smallest repeating structural unit of a crystal lattice that, when repeated in three dimensions, generates the entire crystal.

Define isomorphism and polymorphism.

Isomorphism: different substances having the same crystalline form; polymorphism: a single substance existing in more than one crystalline form.

Distinguish between ionic and covalent bonding.

Ionic bonding involves complete transfer of electrons forming oppositely charged ions held by electrostatic attraction; covalent bonding involves sharing of electron pairs between atoms.

Define electronegativity and its relation to bond polarity.

Electronegativity is the tendency of an atom to attract a shared electron pair; a larger electronegativity difference between bonded atoms creates a more polar bond.

What hybridization, shape, and bond angle correspond to sp, sp2, and sp3?

sp: linear, 180 degrees; sp2: trigonal planar, 120 degrees; sp3: tetrahedral, 109.5 degrees.

According to VSEPR theory, what shape and bond angle does a water molecule have, and why does it differ from tetrahedral?

Water is bent/angular with about 104.5 degrees; two lone pairs on oxygen repel more strongly, compressing the H-O-H angle below 109.5 degrees.

Define bond energy and explain how it relates to bond strength and length.

Bond energy is the energy required to break one mole of bonds in the gaseous state; higher bond energy means a stronger, shorter bond.