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atomic model timeline
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By: Maria Manuela Pereira (9A)
Atomic Theory Timeline
Schrodinger's Atomic Model
Niels Bohr's Atomic Model
Rutherford's Atomic Model
Dalton's Atomic Model
J.J Thomson's Atomic Model
Democritus' Atomic Model
Democritus' Atomic Model (460-360BCE)
He stated that everything (mass) was made of atoms. Atoms were indivisible and undistructable, lacked the ability to move and were solid spheres. Solid atoms differed from liquid atoms. He came up with the idea of an atom.
460-360BCE
Atomic Model
Experiment
As Democritus was a philosopher, he based his theory on his beliefs and philosophical means, and lacked scientific evidence
Experiment
Contribution
Contributions
He laid the base for the atomic theory, and was the first one to recognize an atom, and that living things are made of atoms
Inaccuracies
In Democitus' model, he portrayed the atom as a hard sphere. He lacked any information about the atom's internal structure and composition, such as nucleus, protons, neutrons, and electrons.
Inaccuracies
Dalton's Atomic Model
(1803)
1803
Dalton created the first atomic theory to explain the fundamental laws. Dalton states that 1)each elements' structure differ to other elements' structure, 2)all elements are made up of indivisible parts called atoms, 3)different elements' atoms can combine physically or chemically, 4) chemical reactions are present when atoms are combined, rearranged, or separated, 5) atoms can't be created or destroyed. He also said atoms were hard spheres with no charges, specific sizes or mass. In Dalton's theory, he also stated that since the number of atoms was conserved, the reaction has its mass conserved
Dalton's Atomic Model
Model
Experiment
Dalton used 3 laws to base his atomic theory. The laws were: Law of Conservation of Matter; Law of Definite or Constant Composition; and The Law of Multiple Properties. The usage of all these laws led Dalton to forming his Atomic Theory. The Law of Multiple Property was created by Dalton as a variation of the law of definite proportions.
Experiment
Contributions
Dalton contributed to today's atomic theory by recognizing that atoms of a particular element differ from particles from other elements.
Contributions
Inaccuracies
In Dalton's model, the atom was just a simple ball, as subatomic particles had not been discovered yet. His model lacked information about electrons, protons, nucleus, and neutrons. His theory was later disproved by the discovery of electrons. However, it still enhanced Democritus' atomic theory
Inaccuracies
J.J's Thomson's Atomic Model (1904)
1904
Thomson discovered the existence of electrons in an atom, and compared it to a blueberry muffin (muffin=atom/blueberry=electrons). He made this comparison as blueberries are embended all over the muffin, which represented what he believed about the atom's relationship with the electrons.
J. J. Thomson's Model
Model
Experiment
Thomson discovered the electrons by using the cathode ray (stream of negatively charged atoms) tube, which later became known as the Cathode Ray Experiment
Experiment
Contributions
Thomson was the first one to recognize the existence of electrons in the atom's structure, and also classified an atom as something soft. His model became known as the plum-pudding model as he compared it to an atom
Contributions
Inaccuracies
In Thomson's model, he only showed the electrons, however, no nucleus, protons or neutrons yet. He compared it to a plum pudding due to its texture and the fact that blueberries were embended in it just like electrons. It lacked further information about the atom's inner structure as the nucleus, proton and neutrons. Though, it still enhanced Dalton's previous atomic theory as it mentioned the existence of electrons in an atom
Rutherford's Atomic Model
(1911)
1911
Rutherford discovered the presence of a nucleus in an atom by conducting the gold foil experiment. Through the experiment, he discovered that an atom's mass and positive charge are concentrated in a small area in the middle of the atom that he called the nucleus. Also that the electrons are located outside of the nucleus.
Rutherford's Atom Model
Model
Experiment
Rutherford preformed an experiment with a beam of particles and a gold foil. This experiment became known as the Gold Foil experiment
Experiment
Contributions
Rutherford was the first one to recognize that the positive charge of an atom is located in the nucleus
Contributions
Inaccuracies
Though he was the first one to recognize the positive charge location of an atom, his model still lacked information about why electrons remained in orbit around the nucleus. Even though it lacked many information, he was still able to enhance Thomson's model by implementing information about the positive charge of an atom
Inaccuracies
Niels Bohr's Atomic Model
(1913)
1913
In his atomic theory, Bohr stated: 1) electrons orbit around the nucleus; 2) each electron has a fixed energy that is known as energy level (shells) 3)an electron can "jump" to a different energy level if added energy, and if energy is removed, then it can return by releasing the added energy; 4) there are energy levels around a nucleus that go from 1-7. Energy level 1 is closest to the nucleus which means there's less energy and more stability. On the other hand, level 7 is furthur from the nucleus, which has more energy and are less stable. He portrayed atoms as small positively charged nucleus that have electrons orbiting around it.
Bohr's Model of an Atom
Model
Experiment
Bohr heated hydrogen gas atoms in a tube. It caused the atoms to radiate and release energy. When he viewed it through a diffraction grating, single rays of light with different colors were formed and could be observed. Each color represented a specific transition, and energy emittion. As hydrogen was doing that at the same time, it ended up emitting a pink color. This model explained the spectrum of hydrogen. After discussing the results from his experiment, his atomic model was created. It concluded that if different atoms were exposed to a source of energy, different colors would be seen because the set of transition is specific to each atom
Experiment
Contributions
Bohr explained that electrons orbit in separate and fixed orbits around the nucleus, and that they also have energy levels.
Contributions
Inaccuracies
In Bohr's model, he believed electrons orbited around the nucleus. As it can be seen in nowaday's model, this is not true, that electrons are actually in orbitals. His model was also for hydrogen atoms, though, we still use it for other atoms, there's still room for discoveries to contradict his discovery.
However, it still enhanced the previous atomic model by adding new knowledge to the structure of an atom.
Schrodinger's Atomic Model (1926)
Schrodinger considered Broglie's previous attribution and stated that the electron's behavior could be further explained if they were treated as wave matters. He created an equation to treat the electron as a wave. With that, he found regions around the nucleus where the probability of finding electrons is the largest, and called these regions- Orbitals. He stated that around the nucleus; there was a cloud of electrons. His model took after that statement and became known as the Electron Cloud Model
1926
Schrodinger's Model
Model
Experiment
Based on Bohr's model, Schrodinger created the equation to treat electrons as waves
Experiment
Contributions
Schrodinger's equation solution and discoveries stated that all the orbitals electrons could occupy and all the various values of energy for an electron.Schrodinger also found regions around the nucleus where the probabilities of finding an electrons are the highest, and called that orbital. Along with that, he said electron's behavior could be explained if they were treated as wave matters.
Contributions
Current Atomic Model
Nowadays' model is called the Cloud Model. Here are the characteristics of nowaday's atom:
1)it's indivisible(atom in greek= not divisible)
2)the atom is made up of protons (positively charged); neutrons (no charge); and electrons (negatively charged)
3)the atom is extremely light
4)atoms form molecule and each type of molecule is a combination of numbers of atoms linked up in a specific way
5)atoms are inalterable (during chemical reactions, atoms are not created or destroyed)
6)the mass of an atom is given by the sum of protons and neutrons of the nucleus
7) electrons are in orbitals, not in orbits
8) the energy the electrons assume is the energy level of the orbitals