BDS Admission Test Chemistry Syllabus

What is percentage yield and how is it calculated?

Percentage yield = (actual yield / theoretical yield) x 100; it measures the efficiency of a reaction.

Name the three subatomic particles and their charges.

Proton (+1), neutron (0, neutral), and electron (-1).

Compare the masses of subatomic particles.

Proton and neutron each have a mass of about 1 amu; the electron's mass is about 1/1836 amu (negligible).

What is the atomic number of an element?

The number of protons in the nucleus of an atom, which determines the identity of the element.

What is the mass number of an atom?

The sum of the number of protons and neutrons in the nucleus.

What are isotopes?

Atoms of the same element with the same number of protons but different numbers of neutrons (same atomic number, different mass number).

Who discovered the electron and the proton?

J.J. Thomson discovered the electron; Ernest Rutherford (Goldstein with canal rays) is credited with the proton; the neutron was discovered by James Chadwick.

What are the main postulates of Bohr's atomic model?

Electrons revolve in fixed circular orbits (energy levels) without radiating energy; each orbit has a fixed energy; electrons absorb or emit energy only when jumping between orbits.

In Bohr's model, what happens when an electron jumps from a higher to a lower energy level?

Energy is emitted (released) as a photon of a specific wavelength equal to the energy difference between the levels.

What is the formula for the energy emitted/absorbed during an electron transition?

E = hf (or DeltaE = E_final - E_initial), where h is Planck's constant and f is the frequency of radiation.

What is a major limitation of Bohr's atomic model?

It successfully explains only the hydrogen atom (single-electron systems) and fails to explain spectra of multi-electron atoms, fine spectral lines, and the dual nature of electrons.

What does the principal quantum number (n) describe?

The main energy level or shell of an electron and its average distance from the nucleus; n = 1, 2, 3, ...

What does the azimuthal (angular momentum) quantum number (l) describe?

The subshell and shape of the orbital; l ranges from 0 to (n-1), where l = 0,1,2,3 correspond to s, p, d, f orbitals.

What does the magnetic quantum number (m_l) describe?

The orientation of the orbital in space; it ranges from -l to +l, including zero.

What does the spin quantum number (m_s) describe?

The direction of electron spin; its values are +1/2 and -1/2.

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

s: 1 orbital, 2 electrons; p: 3 orbitals, 6 electrons; d: 5 orbitals, 10 electrons; f: 7 orbitals, 14 electrons.

What are the shapes of s and p orbitals?

The s orbital is spherical; the p orbitals are dumbbell-shaped (oriented along the x, y, and z axes).

State the Aufbau principle.

Electrons fill orbitals in order of increasing energy, starting with the lowest available energy level first.

State the Pauli exclusion principle.

No two electrons in an atom can have the same set of all four quantum numbers; an orbital holds a maximum of two electrons with opposite spins.

State Hund's rule.

Electrons occupy degenerate (equal-energy) orbitals singly with parallel spins before pairing up.

Write the electronic configuration of sodium (Z = 11).

1s2 2s2 2p6 3s1.

What is the maximum number of electrons in a shell (formula)?

2n^2, where n is the principal quantum number.

State Boyle's law.

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

State Charles's law.

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

State Avogadro's law.

At the same temperature and pressure, equal volumes of all gases contain an equal number of molecules (V proportional to n).

What is the ideal gas equation?

PV = nRT, where P = pressure, V = volume, n = number of moles, R = gas constant, and T = absolute temperature.

What is the value of the universal gas constant R?

R = 0.0821 L atm mol^-1 K^-1 (or 8.314 J mol^-1 K^-1).

State the main postulates of the kinetic molecular theory of gases.

Gas molecules are in constant random motion; their volume is negligible compared to the container; there are no intermolecular forces; collisions are perfectly elastic; and average kinetic energy is directly proportional to absolute temperature.

What is a reversible reaction?

A reaction in which the products can react to re-form the reactants, proceeding in both forward and backward directions simultaneously (denoted by a double arrow).

What characterizes the state of chemical equilibrium?

A dynamic state in which the rate of the forward reaction equals the rate of the backward reaction, so the concentrations of reactants and products remain constant over time.