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Period: 460 BCE to 370 BCE
Democritus
He observed that a single "primary matter" existed and it was this primary matter, modified in various ways, that all other things were created. -
400 BCE
Democritus Atomic Model
Democritus's model stated that matter consists of invisible particles called atoms and a void. He stated that atoms are indestructible, unchangeable, and have no internal structure. The atomic model was solid and stated that all atoms differ in size, shape, mass, position, and arrangement, with a void existing between them. Accuracies:
That all matter consists of atoms and all atoms are different.
Inaccuracies:
That there is only one singular thing in an atom. No internal structure. -
Period: to
John Dalton
John Dalton believed matter consists of indivisible atoms. All of the atoms of a given chemical element are identical in mass and in all other properties. Different chemical elements have different kinds of atoms; in particular, their atoms have different masses. Atoms are indestructible and retain their identities in chemical reactions. A compound forms from its elements through the combination of atoms of unlike elements in small whole-number ratios. -
John Dalton Atomic Model
(All elements are composed of atoms.) {It is impossible to divide or destroy an atom. All atoms of the same element are alike.} (Atoms of different elements are different and can combine to form a compound, but have to be in definite whole number ratios. Chemical reactions occur when atoms are separated, joined, or rearranged.) {Atoms of one element are never changed into atoms of another element as a result of a chemical reaction.} Accuracies()
Inaccuracies {} -
Period: to
J.J. Thomson
Thomson discovered the electron when he was experimenting with gas discharge tubes. He noticed a movement in a tube and called the movement cathode rays. The rays moved from the negative end of the tube to the positive end. It was then he realized that the rays were made of negatively charged particles, later to be named electrons. -
Period: to
Hantaro Nagaoka
Nagaoka was reading a discussion from James Clerk Maxwell about electrons when he drew attention to the Saturns Rings. The rings being negatively charged and the center positive. This helped to lead Nagaoka to develop his atomic model the "Saturnian." -
Period: to
Ernest Rutherford
Ernest Rutherford conducted an experiment called the gold foil experiment. He took a thin sheet of gold foil. He used special equipment to shoot alpha particles at the gold foil. Most particles passed straight through the foil like the foil was not there. Some particles went straight back or were deflected as if they had hit something. He concluded that atoms are made of a small positive nucleus because the positive nucleus repels positive alpha particles also that atoms are mostly empty space. -
Period: to
Neils Bohr
All electrons have their energy levels a certain distance from the nucleus. Each energy level can hold a certain number of electrons. Level 1 can hold 2 electrons, Level 2-8 electrons, Level 3-18 electrons, and level 4-32 electrons. The energy of electrons goes up from level 1 to other levels. When electrons release (lose) energy they go down a level. When electrons absorb (gain) energy, they go to a higher level. -
Period: to
Erwin Schrodinger and Werner Heisenberg
They discovered that electrons don't move in orbits or in a set path at all. He theorizes electrons move in waves, and have no exact location. -
Period: to
James Chadwick
James Chadwick's Atomic Theory led to the discovery of neutrons. In it, he bombarded a sheet of beryllium with high energy particles. Other particles came loose, and he named them neutrons. -
Hantaro Nagaoka Atomic Model
Nagaoka believed atoms functioned similarly to the way Saturn and its rings do. He believed there to be one large center positively charged, the nucleus, that had smaller negatively charged particles, electrons, continuously revolving around it. Accuracies:
The nucleus has a positive charge and the electrons are negative.
Inaccuracies:
It is unstable since the electrons would lose energy continuously revolving. -
J.J. Thomson Atomic Model
Thomson’s model was known as the "Plum Pudding Model” He suggested each atom was a sphere filled with a positively charged fluid, known as the “pudding”. Scattered in this fluid were negatively charged electrons, these were the “plums” in the pudding. Thomson suggested that the positive fluid held the negatively charged electrons in the atom because of its electrical forces. Accuracies:
He discovered electrons. Electrical forces held the negative forces. Inaccuracies:
The plum pudding idea. -
Ernest Rutherford Atomic Model
Rutherford proposed that atoms consisted of a small dense center, filled with positive charges, and named this center the nucleus. He then said that negatively charged electrons were scattered surrounding this dense, positively charged center and that these negatively charged electrons were held in orbit by the positively charged nucleus, due to the electrical forces. Accuracies:
The discovery of the nucleus and its positive charge keeping the electrons held in orbit.
Inaccuracies:
No neutrons. -
Neils Bohr Atomic Model
(Bohr stated electrons moved in fixed, circular orbits around the nucleus, called electron shells. These shells were set distances from the nucleus and were the same for all atoms. He stated they became larger the further away they are from the nucleus, and that electrons furthest from the nucleus have higher energy. He identified that an electron can jump from a lower orbit to a higher orbit by absorbing energy, and then lose energy when they are allowed to cool.)
Accuracies()
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Erwin Schrödinger and Werner Heisenberg Atomic Model
The quantum mechanical model of the atom uses complex shapes of orbitals, sometimes called electron clouds, volumes of space in which there is likely to be an electron. So, this model is based on probability rather than certainty. Accuracies:
Electrons move in any direction they want. Introducing electron sub-levels.
Inaccuracies:
No Neutrons -
James Chadwick Atomic Model
This model is about as up to date as it gets with him discovering the neutrons in the nucleus. There are Neutrons and Protons in the nucleus with electrons swirling around it with different energy levels. Accuracies:
Neutrons discovered. Everything is about as up to date as of now.
Inaccuracies:
