It was in 1897 that J. J. Thomson discovered the first subatomic particle, called the electron while studying cathode radiation. In order to explain neutrality in atoms Thomson suggested a model for the atom, in which negatively charged electrons scatter around an atom that is charged with positive energy. Thomson named his model of the atom the plum pudding.
Thomson believed that atoms were homogeneous spheres of positively charged matter, in which electrons are contained. The Plum Pudding model needed to be discarded (1911) in both theoretic and scientific grounds to make way for the adoption of the Rutherford Atomic Model,
Here are the most important aspects of Thomson’s Atomic Model:
1. Due to its style, this model is also known as the plum pudding model.
2. Every atom is a globe filled with positively charged fluid.
3. Corpuscles (later known as electrons) are the negatively charged particles that are suspended in this fluid. It is similar to the plums found in the pudding.
4. He was not able to predict the direction of these electrons.
Thomson conducted his research. Thomson conducted the current through a cathode tube that was similar to the one in the figure below. A cathode tube is an unbreakable glass tube that has almost all air has been taken away. It is made up of metal known as an electrode at each of its ends. One electrode is negative charged and is referred to as an cathode. The opposite electrode has a positive charge and is referred to as an Anode. When a high-voltage electric voltage is applied to ends of plates, the cathode beam is able to travel from the cathode towards the anode.
Cathode tubes are sealed glass tubes, from which the majority of the air is eliminated. They are powered with a voltage that is high to two electrodes on one side of the tube. This creates particles to move through the cathode (the positively charged electrode) to the anode (the positively charged electrode).
Thomson utilized the cathode ray tube using a magnet and observed that the beam of green that it generated consisted of negatively charged materials. Thomson conducted numerous tests and discovered that the weight of one the particles was 22,000 times heavier than the hydrogen atom. Based on this, he concluded that the particles had to have been created somewhere within the atom, and Dalton was
Incorrect in saying that atoms are not able to be divided into pieces smaller than.
Thomson also assessed the mass of particles he discovered. He measured this by determining the extent to which the cathode’s rays bent as he altered the voltage. He discovered that the weight of particles was about 2000 times smaller than that of atom with the smallest mass which is which is the hydrogen atom. It is clear that Thomson was able to identify particles that are smaller than the atoms. Thomson’s discovery disproved Dalton’s assertion that atoms are the most tiny particles in the universe.
Thomson took a step further, and concluded that electrons charged negatively required an element that was positive in order to balance them. Thomson determined that they were in a space surrounded by positively charged matter. This is now known as the “plum pudding” concept of the Atom. The plums that were negatively charged were covered with positively charged dessert.
Limitations of Thomson’s Atomic Model
- Thomson’s atomic model was unable to clarify how the positive charge binds to the electrons in the atom. It also didn’t explain the stability of an atom.
- The theory didn’t mention something about the nucleus an atom.
- It was not able to explain the scattering experiment conducted by Rutherford.
The Bohr model of the atomic structure illustrates the structure of the atom. However, while Bohr was considered to be the first model of atomic structure that included quantum theory and was a fundamental conceptual model for electron orbits wasn’t an accurate representation of the nature of electrons orbiting.
Thomson’s Postulates Atomic Model
Postulate 1: The atom is made up of an positively charged sphere that has electrons embedded within it
Postulate 2: The atom in its entirety is electrically neutral since both positive and negative charges are the same in size
Thomson Atomic Model is compared with watermelon. In his research, Thomson thought about:
- Seeds of watermelon as negatively charged particles
- The red portion of the watermelon that is positively charged
Rutherford Atomic Model
Based on the observations above and conclusion, Rutherford proposed the atomic structure of elements. In accordance with the Rutherford model of the atomic structure:
- The positive charge and the majority part of the weight of the atom is concentrated in a tiny size. He referred to this area of the atom the nucleus.
- Rutherford’s model suggested that negatively charged electrons surround nucleus of the atom. He also suggested that the electrons that surround the nucleus spin around it at a very fast speed , in circular pathways. He referred to the circular paths orbits.
- Electrons, being negatively charged, and the nucleus a concentrated collection made up of positively charged particles are held with a powerful electric force that attracts.
Rutherford model also known as Rutherford nuclear model, atomic model atom, or the planetary model for the atom explanation of the structure and function of atoms suggested (1911) by native of New Zealand, Ernest Rutherford. Models of the atom described it as having a tiny and dense positively charged nucleus (or core) in which the vast majority of the mass is concentrated around which are the positive, light constituents known as electrons,
Rutherford’s concept was to aim powerful alpha particles towards the surface of a thin metal foil to observe the extent to which beams of alpha particles are scattered when it hits an extremely thin metal foil. A narrow collimated beam made of alpha particles was directed towards an aluminum foil with about 1 millimeter thick (about 10,000 atoms). Alpha particles are powerful nuclei of the helium (usually around six MeV). The Alpha particle, around 7300 times bigger than electrons, possess an electric charge of +2e.
The Observations of Rutherford’s Alpha Scattering Experiment
- A significant portion of A-particles that were hurled towards the gold sheet travelled through the sheet without deflection. Therefore, the majority of the space inside an atom is unoccupied.
- The majority of the a-particles were deflected, that is why only a handful of a-particles with a nearly 180o angles of deflection. Therefore, the volume that is occupied by those positively charged particle inside an atom is tiny when compared to the total amount of the atom.
- A-particles are dispersed due to the gold sheets at tiny angles, and consequently the positive charge inside an atom isn’t evenly dispersed. The positive charge within one atom can be concentrated within the smallest amount.
Limitations of Rutherford Atomic Model
- Rutherford’s theory was not able to describe the stability and dependability of an atom. According to Rutherford’s theory, electrons move at a fast speed around the nucleus in an orbit that is fixed.
- Electromagnetic radiation is likely to carry energy due to the electronic motion because from which orbits slowly shrink. The orbits will shrink and then collapse inside the nucleus of the atom. Rutherford the atomic model was not in line with Maxwell’s theory , and could not explain the stability of an atom.
- Rutherford’s theory was insufficient because it didn’t include any details concerning the order of the electrons inside the orbit.
Key Aspects of the Bohr Model
- Electrons orbit around the nucleus in orbits with a specific dimensions and levels of energy.
- The energy of an orbit is determined by the size of its orbit. The lowest energy is located in the orbit with the lowest energy.
- Radiation is absorbed or released as an electron goes between orbits.
The most significant contribution of Bohr to the field of modern physics was his Atomic model. The Bohr model depicts the atom as a tiny positively charged nucleus that is that is surrounded by electrons in orbit.
Bohr is the one person to discover that electrons move in distinct circular orbits about the nucleus, and that the amount of electrons that are in an outer orbit is a factor that determines characteristics of an element.
But it was false in many ways and eventually, it was destined to fail. The growing field of quantum mechanics showed the inability to determine the electron’s velocity and position simultaneously. The well-defined Bohr orbits have been replaced by probabilities “clouds” that show where electrons are likely to be.
Dalton Atomic Model
Dalton Atomic Model Dalton Atomic Model is a model of the atom, which was designed in the late John Dalton. It was built on principles for conservation of mass and constant proportions, as well as multiple proportions as well as reciprocal ratios. The model proposed an atom’s size as tiny and indivisible particles that are spherical and cannot be further divided.
The concept of partial pressures on the notion that like atoms in a mix of gases oppose one another, while different atoms seem to behave with no difference. This theory explained how each gas in a mix behaved differently.
His assertions were built upon the 3 laws we’d talked about earlier. He formulated the following postulates (not the entire list accurate) regarding his theory of atomic physics.
- Atoms are tiny, chemically impervious particles of matter. The elements are made up of atoms.
- Atoms that are combined with one are bound by each other’s Law of Multiple Proportions. That is when elements are combined the ratio at which the atoms are combined can be described as a proportion of whole numbers.
- The elements of the atoms have different properties and differing masses of atoms.
- Atoms of elements have the same properties.
- Atoms that interact with each other follow what is known as the Law of Conservation of Mass.
- The first portion of the postulate 2 was rejected. Bohr’s concept suggested that Atoms could be further split into neutrons, protons, and electrons.
- The third postulate was found to be false due to the existence of isotopes. They are atoms from the exact element, but with different mass.
- This fourth precept was proved to be incorrect due to Isobars which are atoms that belong to different elements, but with identical mass.