ATOMIC MODELS

Dalton’s Atomic Theory:

1. Matter is made up of tiny, indivisible particles called atoms.
2. All atoms of a given element are identical.
3. Atoms combine in simple, whole-number ratios to form compounds.

Thomson’s Model of Atom:

1. Also known as the “plum pudding model,” shows that atoms are composed of positively charged material with electrons embedded within it.
2. Electrons are spread throughout the atom, like plums in a pudding.

Rutherford’s Model of Atom:

1. Based on the gold foil experiment, where a beam of alpha particles was fired at a thin sheet of gold foil.
2. Results showed that most alpha particles passed through the foil, but a small number was deflected at large angles, indicating the presence of a small, dense, positively charged nucleus.

Bohr’s Model of Atom:

1. Proposed that electrons move in fixed circular orbits around the nucleus.
2. Each orbit has a specific energy, and electrons can move from one orbit to another by absorbing or releasing energy.

Quantum Mechanical Model of Atom:

1. Electrons do not move in fixed circular orbits, but rather in three-dimensional orbitals around the nucleus.
2. Orbitals are defined by the quantum numbers that describe the electron’s energy, shape, and orientation.

Dual Nature of Matter:

1. Electrons and photons have both particle and wave properties.
2. Louis de Broglie proposed the wave-particle duality of matter, which states that all matter has both wave and particle characteristics.

Heisenberg’s Uncertainty Principle:

1. States that it is impossible to simultaneously know both the exact momentum and position of a subatomic particle.
2. The more precisely one property is known, the less precisely the other can be known.

Quantum Numbers:

1. Describe the properties of electrons in an atom.
2. Include the principal quantum number (n), angular momentum quantum number (l), magnetic quantum number (ml), and spin quantum number (ms).

Electronic Configuration:

1. The arrangement of electrons in orbitals within an atom.
2. Determined by the Aufbau principle, Pauli’s exclusion principle, and Hund’s rule.

Aufbau Principle:

1. States that electrons fill orbitals in order of increasing energy.
2. Lower energy orbitals are filled before higher energy orbitals.

Pauli’s Exclusion Principle:

1. States that no two electrons in an atom can have the same set of four quantum numbers.
2. Each electron must be unique.

Hund’s Rule:

1. States that electrons in orbitals of the same energy tend to occupy different orbitals with the same spin before pairing up.
2. This maximizes the total spin of the atom.