Democritus was the 1st to suggest the existence of atoms. Democritus was the 1st to suggest the existence of atoms


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Democritus was the 1st to suggest the existence of atoms.

  • Democritus was the 1st to suggest the existence of atoms.

  • He proposed an Atomic Theory which states that all atoms are small, hard, indivisible and indestructible particles made of a single material formed into different shapes and sizes.

  • Although his ideas agreed with scientific theory later, it still did not explain chemical behavior.

  • Aristotle did not support his atomic theory. Democritus‘s approach was not based on the scientific method.



In 1803, proposed an Atomic Theory which states:

  • In 1803, proposed an Atomic Theory which states:

    • All substances are made of atoms; atoms are small particles that cannot be created, divided, or destroyed.
    • Atoms of the same element are exactly alike, and atoms of different elements are different
    • Atoms join with other atoms to make new substances
    • Chemical reactions occur when atoms are separated, joined, or rearranged into different combinations.
  • He was a chemist and a school teacher.



Proved that an atom can be divided into smaller parts

  • Proved that an atom can be divided into smaller parts

  • While experimenting with cathode-ray tubes, discovered electrons

  • Stated that the atom is neutral

  • In 1897, proposed the Plum Pudding Model which states that atoms mostly consist of positively charged material with negatively charged particles (electrons) located throughout the positive material



In 1911, performed the Gold Foil Experiment and suggested the following characteristics of the atom:

  • In 1911, performed the Gold Foil Experiment and suggested the following characteristics of the atom:

    • It consists of a small core, or nucleus, that contains most of the mass of the atom
    • This nucleus is made up of particles called protons, which have a positive charge
    • The protons are surrounded by negatively charged electrons, but most of the atom is actually empty space
  • Did extensive work on radioactivity (alpha & beta particles, gamma rays/waves) and was referred to as the “Father of Nuclear Physics”

  • Was a student of J.J. Thomson



In 1913, proposed the Bohr Model, which suggests that electrons travel around the nucleus of an atom in orbits or definite paths. Additionally, the electrons can jump from a path in one level to a path in another level (depending on their energy)

  • In 1913, proposed the Bohr Model, which suggests that electrons travel around the nucleus of an atom in orbits or definite paths. Additionally, the electrons can jump from a path in one level to a path in another level (depending on their energy)

  • Won a Nobel Prize

  • Worked with Ernest Rutherford





How did the concept of the atom change from the time of Democritus to the time of Dalton?

  • How did the concept of the atom change from the time of Democritus to the time of Dalton?

    • Democritus reasoned that atoms were indivisible and indestructible. His theory was not based on the scientific method. Dalton transformed Democritus’s idea using experimental methods and turned the ideas of atoms into scientific theory.


An atom is the smallest particle of an element that retains its identity in a chemical reaction.

  • An atom is the smallest particle of an element that retains its identity in a chemical reaction.

  • The atom is composed of 3 subatomic particles:

    • Proton: Positively charged
      • Symbol: p+
      • Relative Mass: 1
    • Neutron: No charge
      • Symbol: n0
      • Relative Mass: 1
    • Electron: Negatively charged
      • Symbol: e-
      • Relative Mass: 0


Atomic number: is the number of protons in the nucleus of an atom of an element.

  • Atomic number: is the number of protons in the nucleus of an atom of an element.

  • Mass number: is the total amount of protons and neutrons in an atom.

    • To find the number of neutrons just subtract
    • Mass number – atomic number = # of neutrons
  • Isotopes: Atoms that have the same number of protons but different number of neutrons.



Protons:

  • Protons:

  • Neutrons:

  • Electrons:

  • Element Name:

  • Symbol:



Protons:

  • Protons:

  • Neutrons:

  • Electrons:

  • Element Name:

  • Symbol:




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