Describe the changes that have happened to the model of the atom over time. (6)
1. Thomson's Plum Pudding Model: In the late 1800s, J.J. Thomson proposed that atoms were made up of a positively charged "pudding" with negatively charged electrons scattered throughout. This model was based on his discovery of electrons.
2. Rutherford's Nuclear Model: In 1911, Ernest Rutherford conducted the gold foil experiment and discovered that atoms had a small, dense, positively charged nucleus at the center, surrounded by negatively charged electrons. This model formed the basis of modern atomic theory.
3. Bohr's Planetary Model: In 1913, Niels Bohr proposed that electrons moved in fixed orbits around the nucleus, similar to the way planets orbit the sun. He also suggested that electrons could only move between these orbits by absorbing or emitting energy.
4. Wave Mechanical Model: In the late 1920s, Erwin Schrödinger and Werner Heisenberg developed the wave mechanical model, which proposed that electrons do not follow fixed orbits but instead exist in a probability cloud around the nucleus. This model is based on the idea of wave-particle duality.
5. Quantum Field Theory: In the mid-20th century, physicists developed quantum field theory, which describes subatomic particles as different excitations of underlying quantum fields. This theory is more complex and abstract, but it is able to accurately predict the behavior of subatomic particles.
6. Modern Developments: Modern atomic theory includes advancements such as the discovery of more subatomic particles beyond electrons, protons, and neutrons, as well as exploration into the behavior of antimatter and dark matter. Scientists continue to refine the models of the atom in order to better understand the nature of matter and energy.
1. Dalton's Atomic Theory: In the early 19th century, John Dalton proposed the first atomic model known as Dalton's Atomic Theory. According to this theory, atoms were considered indivisible and indestructible particles that combined in fixed ratios to form compounds. Atoms were thought to be tiny, solid spheres with no internal structure.
2. Thomson's Plum Pudding Model: In 1897, J.J. Thomson discovered the existence of electrons through his experiments with cathode rays. He proposed a new atomic model known as the Plum Pudding Model. According to this model, the atom was a positively charged sphere with negatively charged electrons embedded within it like plums in a pudding.
3. Rutherford's Nuclear Model: In 1911, Ernest Rutherford conducted the famous gold foil experiment that led to the discovery of the atomic nucleus. He proposed a new atomic model known as the Nuclear Model. According to this model, the atom consists of a tiny, dense, positively charged nucleus at the center, surrounded by negatively charged electrons that orbit the nucleus like planets around the sun.
4. Bohr's Planetary Model: In 1913, Niels Bohr built upon Rutherford's model and proposed the Planetary Model of the atom. Bohr suggested that electrons exist in specific energy levels or shells around the nucleus. These electrons can move between energy levels by absorbing or emitting specific amounts of energy. This model explained the line spectra observed in atomic spectroscopy.
5. Quantum Mechanical Model: In the 1920s, the Quantum Mechanical Model replaced Bohr's model. This model incorporates the principles of quantum mechanics and suggests that electrons do not move in definite orbits but rather occupy certain regions of space called electron clouds or orbitals. These orbitals represent the probability of finding an electron at a particular point around the nucleus, rather than a specific path.
6. Modern Atomic Model: Currently, the most widely accepted atomic model is the Modern Atomic Model. It is based on the quantum mechanical model but includes more complex concepts such as electron spin, electron configuration, and the Pauli exclusion principle, which states that no two electrons in an atom can have the same set of quantum numbers. This model helps explain the behavior and properties of atoms and is used to understand chemical reactions and bonding.