What is an atom?
The smallest unit of an element that can participate in a chemical reaction.
What is a molecule?
The smallest particle of a substance that can exist independently and retain the chemical properties of that substance.
What does atomicity refer to?
The number of atoms in a molecule of an element.
Give examples of monatomic, diatomic, and triatomic elements.
Monatomic: He; Diatomic: O₂, H₂; Triatomic: O₃.
What is an ion?
An atom or group of atoms carrying a positive or negative charge.
What are radicals?
Charged groups of atoms that retain their identity during reactions.
What are cations?
Positively charged ions, e.g. Na⁺, Ca²⁺, NH₄⁺.
What are anions?
Negatively charged ions, e.g. Cl⁻, SO₄²⁻, CO₃²⁻.
What did Dalton propose in his atomic theory (1808)?
Matter is made up of indivisible atoms that combine in simple ratios to form compounds.
One limitation of Dalton’s theory?
Atoms are divisible into subatomic particles (protons, neutrons, electrons).
What did Thomson’s model describe?
The atom as a uniform sphere of positive charge with embedded electrons — “plum pudding model.”
What was Thomson’s major discovery?
The charge-to-mass ratio (e/m) of electrons is constant for all cathode rays.
What did Rutherford’s model propose?
The atom has a dense, positively charged nucleus with electrons orbiting around it.
What were the limitations of Rutherford’s model?
It could not explain line spectra and predicted atoms should be unstable.
What did Bohr’s atomic model introduce?
Electrons move in fixed orbits called energy levels, with quantized energy.
What does quantization of energy mean?
Electrons can only occupy specific discrete energy levels.
What happens when an electron jumps between energy levels?
It absorbs or emits energy as photons.
What did Bohr’s model successfully explain?
Line spectra of hydrogen and atomic stability.
What are the three subatomic particles?
Proton, neutron, and electron.
Where are protons and neutrons located?
In the nucleus.
What is the relative charge and mass of a proton?
Charge: +1; Mass: 1 unit.
What is the relative charge and mass of a neutron?
Charge: 0; Mass: 1 unit.
What is the relative charge and mass of an electron?
Charge: −1; Mass: 1/1840 unit.
What are shells or energy levels?
Fixed paths where electrons move around the nucleus.
What symbol and number correspond to the K shell?
K = 1st shell, n = 1.
What is the formula for the maximum number of electrons in a shell?
2n²
How many electrons can the M shell (n=3) hold?
2(3)² = 18 electrons.
What are sub-energy levels labeled as?
s, p, d, and f.
How many orbitals are in each sublevel?
s=1, p=3, d=5, f=7.
What is the formula for the total number of orbitals in a shell?
n²
How many orbitals are in the N shell (n=4)?
4² = 16 orbitals.
How many electrons can each orbital hold?
Two electrons with opposite spins.
What does the Aufbau Principle state?
Electrons fill orbitals in order of increasing energy — lowest first.
What does Pauli’s Exclusion Principle state?
No two electrons can have the same set of quantum numbers.
What does Hund’s Rule state?
Degenerate orbitals are occupied singly before pairing occurs, with parallel spins.
What is meant by a ground state configuration?
The most stable electron arrangement when orbitals are filled following these rules.
What does the principal quantum number (n) represent?
The main energy level of an electron; values are 1, 2, 3, …
What does the azimuthal (angular momentum) quantum number (l) describe?
The shape of the orbital; values range from 0 to n − 1.
What does the magnetic quantum number (m) indicate?
The orientation of an orbital in space; values range from −l to +l.
What does the spin quantum number (s) describe?
The spin direction of an electron, +½ or −½.
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