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465 BCE
Democritus' atomic theory
“The universe is composed of two elements: the atoms and the void in which they exist and move.”
This is Democritus' atomic theory exactly:
1.All matter consists of invisible particles called atoms.
2. Atoms are indestructible.
3. Atoms are solid but invisible.
4. Atoms are homogenous.
5. Atoms differ in size, shape, mass, position, and arrangement. *FUN FACT: Democriticus was called: The Laughing Philospopher because of his emphasis on the value of ‘cheerfulness, -
Teachings of the Medieval Alchemists
-All matter was composed of four elements.
-EARTH> AIR> FIRE> WATER
-Alchemists were the ones that made the foundations for chemists they had the techniques and array of substances ready.
-Without alchemists, chemists would've had to invent all the general teachings of chemistry. Making the growth of science slower by a century or two
FUN FACTS:
Alchemists would usually heat the metals in a special glass crucible of pear shape. The glass crucible was known as Philosophers’ Egg. -
Dalton’s Law of Partial Pressures
"Dalton's law (also called Dalton's law of partial pressures) states: That in a mixture of non-reacting gases, the total pressure exerted is equal to the sum of the partial pressures of the individual gases" -
Dalton's atomic theory
- Dalton's atomic theory proposed that all matter was composed of atoms, indivisible and indestructible building blocks. While all atoms of an element were identical, different elements had atoms of differing size and mass.
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Daltonism
Dalton believed that his vitreous humor was tinted blue. In experiments presented, DNA extracted from his preserved eye tissue showed that Dalton was a deuteranope, lacking the middlewave photopigment of the retina. Daltonism is actually caused by the eye's light-sensitive cells, known as cones, being faulty or missing. FUN FACT:He started his observations and researches about color vision. his younger brother and John himself both were affected by red-green color blindness. -
Joseph John Thomson a.k.a J.J Thompson
His research in cathode rays led to the discovery of the electron (corpuscles)
Determined all matter made of tiny particles that are smaller than atoms.
Discovered neon was composed of 2 different kinds of atoms, proved existence of isotopes in stable element.
FUN FACTS:
He published several important papers on mathematical and experimental electromagnetism. -
Marie and Pierre Curry Atomic Theory
-Known for their pioneering work in the study of radioactivity, led to the discovery in 1898 of the elements radium and polonium.
-The works of both of them, nature dealt with changes in the atomic nucleus, led the modern understanding of the atom can be split to release enormous energy. -
Neils Bohr
-Came up with a revolutionary theory on atomic structures and radiation emission
-Research led to theorize a series of articles that atoms give off electromagnetic radiation.
-Helped clarify several problems with quantum physics (complementarity/fission)
-First to discover that electrons travel in separate orbits around the nucleus, outer orbit determines the properties of an element.
FUN FACT: During WWII, Bohr offered a place for Jewish Scientists to live and work -
Henri Becquerel discovers radioactivity
Henri Becquerel used naturally fluorescent minerals to study the properties of x-rays, He exposed potassium uranyl sulfate to sunlight and then placed it on photographic plates wrapped in black paper, believing that the uranium absorbed the sun’s energy and then emitted it as x-rays. This theory was disproved but he went on, To his surprise,the images were strong and clear, proving that the uranium emitted radiation without an external source of energy such as the sun. Discovering radioactivity. -
Rutherford's discovery of alpha and beta radiation
Starting in 1898 Rutherford studied the radiation emitted by uranium. He discovered two different types of radiation, which he named alpha and beta.By allowing radiation from uranium to pass through an increasing number of layers of metal foil, he discovered that:
-Beta particles have greater penetrating power than alpha rays
By the direction of their movement in a magnetic field, he deduced that:
-Alpha particles are positively charged
-Alpha particles are helium ions carrying a 2+ charge -
Rutherford's discovery of the atomic nucleus
The results of Rutherford's gold foil experiment allowed him to build a more accurate model of the atom, in which nearly all of the mass was concentrated in a tiny, dense nucleus. Most of the atom’s volume was empty space. The nucleus was like a fly floating in a football stadium – remembering of course that the fly was much heavier than the stadium! Electrons orbited at some distance from the nucleus. This was called the Rutherford model. It resembles planets orbiting a star. -
Rutherford's discovery of nuclear reactions
Rutherford achieved the first deliberate transformation of one element into another. In 1919 he converted nitrogen atoms into oxygen atoms by bombarding nitrogen with alpha particles. This nuclear reaction was written: 14N + α → 17O + 1H FUN FACT: The element 'rutherfordium' was named in his honor -
Rutherford's discovery of the proton
Finding hydrogen produced in the nuclear reaction above, Rutherford began to suspect that the hydrogen nucleus may actually be a fundamental particle, a building block of all atomic nuclei. He formalized this in 1920 by giving this particle a name: the proton. The first nuclear reaction could now be rewritten: 14N + α → 17O + proton -
James Chadwick, The Neutron
Chadwick drew the conclusion that the protons had actually been hit by the particle he was looking for: the neutron. Using polonium as a source of (what he believed were) neutrons, he bombarded wax. Protons were released by the wax and Chadwick made measurements of the protons’ behavior.The protons behaved in exactly the manner they ought to if they had been hit by electrically neutral particles with a mass similar to the proton. Chadwick had discovered the neutron.
