Atom and Atomic Theory
An atom is the fundamental unit of matter, consisting three sub-atomic particles proton, neutron and electron. Two of the sub-atomic particle (proton and electron) of the atom is electrically charge and one sub-atomic particle (neutron) has no charge.
Atom consist a nucleus made up of two sub-atomic particle protons and neutrons, which form a dense and positively charged core, while negatively charged third sub-atomic particle electrons form an electron cloud around the nucleus.
- The chemical properties of an atom are determined by the negatively charged electrons masking the nucleus.
- The physical properties of an atom are determined by the number of protons and neutrons in the nucleus of an atom.
Electrical Charge on three sub-atomic particles:
- Protons carry a positive (+1) electrical charge
- Neutrons have no electrical charge (0)
- Electrons carry a negative (-1) electrical charge
Atomic Nucleus/Nuclei
Atomic nuclei is a dense core of an atom comprised of electrically positive charged proton and electrically neutral neutron held together with a strong force. The nucleus accounts for less than 0.01% of the atom’s volume but more than 99.9% of its mass.
The number of protons in nucleus of an atom is the atomic number, and the number of protons plus neutrons is the atomic mass.
In 1911, Ernest Rutherford discovered that at the core of every atom is a nucleus.
Ernest Rutherford, the discovery of the proton is credited to Ernest Rutherford. Rutherford is also credited with the discovery of the atomic nucleus.
Sir James Chadwick, Sir James Chadwick (1891–1974) was a British physicist who is best known for his discovery of the neutron. For his revolutionary discovery of the neutron in 1932, he was granted the 1935 Nobel Prize in Physics.
J.J. Thomson, is a British physicist discovered electron in 1897.
George Johnstone Stoney, an Irish physicist, is credited with introducing the term “electron”.
Atomic Models
Atomic models are conceptual frameworks used to understand the structure and behavior of atoms. From the early plum pudding model to modern quantum mechanical models, these representations have evolved, revealing the complex nature of atomic particles and their interactions and shaping our understanding of the universe. Here are some of these models:
John Dalton’s Atomic Theory (1803): Dalton suggested that:
- All matter is made up of atoms.
- All matter is composed of indivisible and indestructible atoms.
- Atoms of the same element are identical, but atoms of different elements vary in size and mass.
- Chemical reactions involve rearrangement of atoms to form products.
J.J. Thomson’s Model (1897): Thomson discovered the electron and proposed the “plum pudding” model.
- He proposed that atoms contain a positively charged sphere with embedded electrons.
- Electrons are distributed throughout the atom.
Ernest Rutherford’s Model (1911): Rutherford conducted the famous gold foil experiment:
- Discovered the nucleus.
- He proposed that most of an atom’s mass is concentrated in the nucleus. The nucleus is positively charged and electrons orbit around the nucleus.
- Protons and neutrons are collectively called nucleons.
Niels Bohr’s Model (1913): Bohr introduced the concept of quantized energy levels. He proposed that electrons move in specific orbits or energy shells and can jump between energy levels by absorbing or emitting energy. Energy is absorbed when an electron jumps from a lower orbit to a higher one and energy is emitted when an electron falls from a higher orbit to a lower orbit.
Quantum Model or Quantum-Wave Model or Quantum Mechanical Model (1926): Proposed by Erwin Schrodinger, in 1926.This model blends physics and mathematics. The Quantum Mechanical Model describes the behaviour of electrons in atoms as both particles and waves.
