-
460 BCE
Democritus
Main contribution:
“Matter as made up of tiny
individual particles called
atoms. Atoms could not
be created, destroyed or
further divided.” -
460 BCE
Billiard Ball
Description: His atomic model was solid, and stated all atoms differ in size, shape, mass, position and arrangement, with a void exists between them.
Video explicativo
*It is wrong because, the atom can changed and be divided into subatomic particles. -
John Dalton
Main contribution:
*Atoms of a given element are identical in size,
mass, and chemical properties. Different from
different elements.
*Atoms of two or more different elements combine
to form compounds. A particular compound is
always made up of the same kind of atoms and in
the same proportions.
*A chemical reaction involves the rearrangement,
separation, or combination of atoms. -
Billiard ball
Description: His atomic model stated that there are different types of atoms, these are called elements. Each of the elements is different from one another only by its weight. Dalton used symbols to represent the elements.
Video explicativo
*It is wrong because, it doesn't considered the ions, and the smallest part of a compound isn´t the molecule. -
Joseph John Thomson
Experiment: He applied electricity to a glass tube and produced streams of small particles calles cathode rays. Then, particles must be negatively charged, they were called atoms.
Main contribution: Atoms are neutral, thus the sphere contains the same quantity of positive and negative charges. -
Plum pudding model
Description: As 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.
Video explicativo
*But it is wrong, this wasn't exactly a mass, he didn't distribute well the subatomic particles. -
Lord Rutherford
Experiment: Performed a series of experiments with radioactive alpha particles. He fired tiny alpha particles at solid objects such as gold foil. He found that while most of them passed through at an angle and some bounced straight back. Matter in general had holes in it.
Main contribution: Atoms consisted mostly of empty space through which the electrons move. Almost all positive charge and mass were contained in a dense region in the center: the nucleus -
Planetary model
Description: He stated these negatively charged electrons were held in orbit by the positively charged nucleus, due to the electrical forces. And the model demonstrated that atoms are mostly empty space.
Video explicativo
*It is wrong because, didn't consider the loss of energy in the electrons. Contradicts the electromagnetic theory. -
Niels Bohr
Main contribution: Bohr theorize that electrons only have certain energies in an atom and they had to be in energy levels.
Experiment: He observed the atomic emissions spectrum of the hydrogen atom. When white light is diffracted with a prism, all the colors of the visible spectrum can be seen, each color corresponds to a specific amount of energy; however when the light given off by the hydrogen atom was passed through a prism, only certain colors of light could be seen. -
Energy level model
Description: The electrons go around the nucleus like planets orbit around the sun. All electrons have their energy levels. Each energy level can hold a certain number of electrons. When electrons release energy they go down a level and when the absorbed, they go to a higher level.
video explicativo
*It is wrong 'cause, the orbits should be elliptical like the planetary system. -
Erwing Schrödinger
Main contribution: Electrons move in waves. Electrons can be found in a particular volume of space around the nucleus. The region around the nucleus that describes the electron's probable location is called atomic orbital.
Experiment: He used mathematical equations to describe the likelihood of finding an electron in a certain position. -
Quantum Atomic model
description: Predicts the odds of the location of the electron. This model can be portrayed as a nucleus surrounded by an electron cloud. Where the cloud is most dense, the probability of finding the electron is greatest, and conversely, the electron is less likely to be in a less dense area of the cloud. Thus, this model introduced the concept of sub-energy levels.
*This is the modern model, but we know that this is not the way atoms look like, it is only a way to explain it. -
James Chadwick
Main contribution: He discovered the neutron.
Experiment: He bombarded beryllium atoms with alpha particles. An unknown radiation was produced. Chadwick interpreted this radiation as being composed of particles with neutral electrical charge and the approximate mass of a proton. -
Chadwick's model
Description: People thought the atom was made up of only protons and electrons. The neutron was very hard to find because it did not repel the protons when it was in the atom. With the discovery of the neutron, an adequate model of the atom became available to chemists.
*The orbits were wrong, nowadays we know that the orbits are not circles.
