Chemistry Test Flashcards
What did Dalton’s atomic theory conclude?
In conclusion, Dalton’s atomic theory aimed to explain the properties of atoms and their chemical combination with other atoms of different elements. Dalton’s theory of partial pressure also therefore concluded that atoms of different elements are different and have different properties.
What and whose model superseded Dalton’s and how did Dalton improve on it?
The previous and overarching theory of the atom was “Atomos” which literally meant indivisible this model was made by Democritus in Ancient Greece. Democritus hypothesized that all matter was made of extremely small indivisible particles called atoms. Dalton improved Democritus’ theory of the atom by introducing experimental evidence and outlining tested laws. This made Dalton the pioneer of atomic theory and he proposed the first ever comprehensive atomic theory which clearly stated his viewpoints of the properties of atoms and their behaviours in combinations with atoms of other elements based on Democritus’ empirical evidence.
Two Limitations to Dalton’s Theory
This theory was later shown to be erroneous as his theory was not applicable for component gases being mixed at high temperature and low pressure which were affected by the increases kinetic energy of the particles of the mixture resulting from the high temperature of the component gases, disproving the ideal gas behavior and the theory itself. He also failed to account for isotopes in Dalton stating that all atoms have the same sizes and masses if they are of the same element. Isotopes are atoms of the same element with different masses due to added number of neutrons.
J.J Thomsons Experiment
Thomson conducted the cathode ray tube experiments. Cathode ray tubes are glass tubes which are vacuum inside. A high voltage is applied to one side of the tube across two electrodes, a cathode and an anode which causes a beam of particles (electrons) to move from the cathode to the anode. This beam is detected by a painting of a material called phosphors on to the far end of the tube beyond the anode. The phosphors react and emit light when impacted by the cathode ray. To further test the properties of these particles, Thomson placed two oppositely charged plates on either side of where the cathode rays passed. The cathode ray deflected away from the negatively charged plate which led to the understanding that the particles were negatively charged. The results of these experiments led to the discovery that the previously unknown “electron” particle was a much smaller particle than the atom meaning that it must be subatomic. His findings were supported by the evidence of the law of opposite attraction. It was also supported by the finding that across all the different elements tested by the cathode ray tube experiment, all of them behaved the same when faced with the experiment meaning that electrons must be a common particle to all atoms.
J.J Thomson’s Atomic Model determined and how it improved our understanding of the structure of the atom?
J.J Thomson derived the “Plum-Pudding” model from his cathode ray experiments. Thomson knew that as atoms have a neutral charge, there must be a counter-acting positive charge source balancing the atom. On this understanding, he proposed the plum-pudding which outlined a model of the atom in which electrons are floating in a soup of diffuse positive charge. This model improved our understanding of the structure of the atom as Thomson found the first subatomic particle, an electron which is key to our modern atomic model. He also helped our understanding that electrons are common to all atoms. He also outlined that there must be a positive force counter-balancing the negative forces of the electrons in the atom which remains true with the discovery of protons.
What model superseded Thomson’s model and how did Thomson improve upon it?
The previous and overarching theory of the atom was “Atomos” which literally meant indivisible this model was made by Democritus in Ancient Greece. JJ. Thomson did not disagree with this theory of Democritus but added upon it with his understanding of electrons and a balancing positive charge. Neither did he disagree with Dalton’s understanding but added upon his understanding of the atom’s properties by adding a model and his understanding of electrons and positive balance in an atom.
2 Limitations of Thomson’s Model
The Plum- Pudding model had many limitations. Firstly, it failed to explain the concentrated central position of the positive charge in the nucleus accurately. Secondly, it failed to show how positive charge holds negative charge. There are many more limitations that came about with the advancement of experimental evidence and theory.
General information for Ernest Rutherford
Rutherford was a New Zealand Born Physicist who moved to England and worked at the University of Cambridge the University of Manchester. It was in 1907 that Rutherford conducted the experiments that led to the publishing of his model in 1911
Rutherford’s Experiment
Rutherford conducted the ‘gold foil experiment’ as part of his research. Rutherford and his team bombarded a thin golden foil with alpha particles (particles with 2 neutrons and 2 protons) from a radioactive source. They then observed the scattering pattern of the alpha particles as they passed through the gold foil and recorded the deflection angles. J.J Thompson’s previous model stated that an atom was electrons dispersed throughout a ‘soup’ of positive charge. This led to Rutherford thinking that this alpha particle would go through the gold atoms with little deflection due to the even dispersion of positive charge in J.J Thomson’s model balanced by the negative electron charge. Most alpha particles passed straight through while some of the alpha particles paths were deflected, some very significantly. The alpha particles that did pass through unaffected led to Rutherford hypothesizing that an atom is mostly empty space. He also hypothesized based on this experiment that the alpha particles that deflected at significant angles must have been encountered with a highly concentrated positive charge in a small region of the atom which Rutherford dubbed the ‘nucleus’. The gold-foil experiment heavily supported these claims.
Rutherford’s atomic model and how it improved our modern understanding of atomic structure?
Rutherford derived his own model called the Rutherford’s atom which he determined using his experimental evidence and research. His model highlighted the presence of a highly concentrated area of positive charge called the nucleus at the centre of the atom which was surrounded my negatively charged electrons orbiting the nucleus. It also showed that there was mostly empty space in the atom in between these areas of charge.
Atomic model before Rutherford and how it was improved on or changed?
The previous model was that of J.J Thomson’s Plum Pie model. Rutherford’s model revolutionised our understanding of the atom structure by introducing the idea that the positive charge in the atom is not distributed throughout the whole atom but instead concentrated in the central region of the atom called the nucleus. He also discovered that electrons orbit this region of the nucleus. Rutherford also introduced the idea of empty space between both positive and negative charges in the atom.
Limitations of Rutherford’s model
Rutherford’s model fails to include the presence of neutrons in the nucleus along with protons. It also has the limitation of not defining the circular movement of electrons. Any particle that moves constantly in a circular motion would eventually accelerate causing radiation and therefore energy loss. This would mean that eventually the electrons would lose all its energy and fall into the nucleus.
Niels Bohr General Information
Neils Bohr was a Danish Physicist who worked and lived in Copenhagen, Denmark, teaching students and conducting research. Bohr proposed and published his atomic model in 1913.
Neil Bohr’s Experiment
Bohr observed hydrogen spectral lines especially the Balmer series which reflected Bohr’s model which highlighted the quantization of energy levels. Experiments involving the photoelectric effect and other such phenomena provided further support to Bohr’s model which outlined the quantized natured of energy in atomic systems.
Atomic model determined from Bohr’s experiments and how it improved our understanding of the structure of the atom
Bohr developed the atomic model called the planetary model. Proposed that electrons orbit the nucleus in fixed energy levels and at a fixed distance from the nucleus. Electrons that orbit shells that are further from the nucleus, will exist at higher energy levels and vice versa. Bohr stated that with the addition or removal of energy from the atom, electrons can be promoted or demoted to different energy states proportional to the energy they gain or lose. The gaining of energy in an atom brings electrons to an “excited state” if they have enough energy. If the energy is removed, the electrons return to the original “ground state”. This results in a photon being emitted. A photon is a light particle that has no mass or charge. Bohr’s model effectively accounted for the distinct spectral lines observable in the hydrogen emission spectra by associating them with transitions between quantized energy levels. Each spectral line on the spectra represents a transition between energy levels and the energy emitted or absorbed corresponds to the frequency or wavelength of the energy absorbed or emitted. Bohr’s model significantly influenced the modern understanding of the atom’s structure and especially that of the regions where electrons occupied also referred to as quantized energy levels. It also explains the modern understanding on photo emission and absorption caused by the excitation of electron.
