Pakistan Competitive Exam

Part I Concepts and Terms Related to Atomic Structure

Atom:

Nucleus:

Proton:

Neutron:

Electron

Element:

Atomic Number:

Atomic Mass

Isotope:

Electron Cloud:

Energy Level:

Subatomic Particle

Quantum Mechanics:

Shell:

representing

Subshell:

Part II Concepts and Terms Related to Atomic Structure

1. Orbital:

A region of space around the nucleus where an electron is likely to be found, based on its energy level and angular momentum.

2.Pauli Exclusion Principle:

The principle stating that no two electrons in an atom can have the same set of four quantum numbers, prohibiting the existence of identical quantum states in an atom.

3. Valence Electron

: An electron in the outermost energy level of an atom, responsible for the chemical properties and reactivity of the atom.

4. Principal Quantum Number:

A quantum number representing the energy level of an electron in an atom, determining the size and energy of the orbital.

5. Angular Momentum Quantum Number:

A quantum number representing the shape of the orbital in which an electron is found, determining the subshell and orbital shape.

6. Magnetic Quantum Number:

A quantum number representing the orientation of the orbital in space, determining the spatial orientation of the orbital.

7. Spin Quantum Number:

A quantum number representing the intrinsic angular momentum or spin of an electron, which can have two possible values, +1/2 or -1/2.

8,Aufbau Principle

The principle stating that electrons fill atomic orbitals of the lowest available energy levels before occupying higher levels.

9. Hund's Rule:

The rule stating that electrons occupy orbitals of the same energy in a way that maximizes the total spin, leading to the stability of the atom.

10.Ionization Energy:

The energy required to remove an electron from an atom or ion in the gaseous state.

11. Electron Configuration:

The distribution of electrons of an atom or molecule in atomic or molecular orbitals.

12. Atomic Spectrum:

12. Atomic Spectrum: The unique spectrum of light emitted or absorbed by an element, used to identify elements and study their atomic structure.

13. Excited State:

The state of an atom in which an electron has absorbed energy and moved to a higher energy level, temporarily destabilizing the atom.

14. Ground State:

The lowest energy state of an atom or molecule, with all electrons in the most stable orbitals.

15. Photon:

A quantum of light or other electromagnetic radiation, often emitted or absorbed during transitions between energy levels in atoms.

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The Famous Theories Related to Atomic Structure

1. Dalton's Atomic Theory (1808)

: John Dalton proposed that all elements are composed of indivisible and indestructible atoms, each having its own unique properties. This theory laid the foundation for modern atomic theory and marked the beginning of our understanding of the fundamental building blocks of matter.

2. Thomson's Discovery of the Electron (1897):

J.J. Thomson's experiments with cathode ray tubes led to the discovery of the electron, a subatomic particle with a negative charge. His findings provided evidence for the existence of subatomic particles within atoms and suggested that atoms are divisible into even smaller components.

3. Rutherford's Nuclear Model (1911):

Ernest Rutherford's gold foil experiment demonstrated that atoms have a small, dense, positively charged nucleus at their center, around which negatively charged electrons orbit. This discovery laid the groundwork for the development of the nuclear model of the atom, fundamentally altering the prevailing understanding of atomic structure.

4. Bohr's Model of the Hydrogen Atom (1913):

Niels Bohr proposed a model of the hydrogen atom based on quantum theory, suggesting that electrons orbit the nucleus in discrete, fixed energy levels. This model explained the spectral lines of hydrogen and provided a conceptual framework for understanding the behavior of electrons in atoms.

De Broglie's Matter Wave Hypothesis (1924)

5. : Louis de Broglie postulated that particles, including electrons, exhibit wave-like properties, known as matter waves. This hypothesis suggested that particles can display both particle-like and wave-like behaviors, contributing to the development of quantum mechanics and our understanding of atomic and subatomic phenomena.

6. Heisenberg's Uncertainty Principle (1927):

Werner Heisenberg's principle stated that the more precisely the position of a particle is known, the less precisely its momentum can be known, and vice versa. This principle highlighted the limitations of simultaneously measuring certain pairs of properties of a particle and emphasized the probabilistic nature of quantum mechanics.

7. Schrödinger's Wave Equation (1926):

Erwin Schrödinger formulated a wave equation that describes the behavior of electrons in atoms and molecules. This equation provided a mathematical framework for understanding the wave-like behavior of particles and has been instrumental in the development of quantum mechanics.

8.Pauli Exclusion Principle (1925):

Wolfgang Pauli proposed that no two electrons in an atom can have the same set of quantum numbers, leading to the concept of electron spin and the development of the theory of electron configurations and the periodic table.

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Scientists and Their Discoveries related to Atomic Structure

1.John Dalton (1766-1844)

1.John Dalton (1766-1844): Dalton proposed the atomic theory, which revolutionized chemistry by suggesting that all matter is composed of indivisible particles called atoms.

2.J.J. Thomson (1856-1940):

Thomson discovered the electron through his experiments with cathode rays, contributing to the understanding of atomic structure and the existence of subatomic particles.

3.Ernest Rutherford (1871-1937)

: Rutherford conducted the gold foil experiment and proposed the nuclear model of the atom, suggesting the existence of a small, positively charged nucleus within an atom.

4. Niels Bohr (1885-1962):

Bohr developed the Bohr model of the atom, which introduced the concept of discrete electron energy levels and helped explain the spectral lines of hydrogen.

5. Louis de Broglie (1892-1987): De Broglie proposed the wave-particle duality theory, suggesting that particles, including electrons, exhibit both particle-like and wave-like properties.

6. Werner Heisenberg (1901-1976):

Heisenberg formulated the uncertainty principle, highlighting the limitations of simultaneously measuring certain pairs of properties of a particle and emphasizing the probabilistic nature of quantum mechanics.

7. Erwin Schrödinger (1887-1961):

Schrödinger developed the wave equation that describes the behavior of electrons in atoms and molecules, contributing to the development of quantum mechanics.

8.Max Planck (1858-1947):

Planck introduced the concept of quantized energy, suggesting that energy is not emitted or absorbed continuously but in discrete packets or quanta.

9.Wolfgang Pauli (1900-1958)

Pauli formulated the exclusion principle, which states that no two electrons in an atom can have the same set of quantum numbers, leading to the development of the theory of electron configurations.

10. Linus Pauling (1901-1994):

Pauling made significant contributions to the understanding of the chemical bond, introducing the concept of electronegativity and elucidating the nature of chemical bonding in complex molecules.

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Pakistan Competitive Exam

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