Timeline for Atomic Theory:
2. J Dalton:
Even after Democritus’s suggestion of the existence of an atom, it took almost 2 millenia before the atom was established as a fundamental chemical object by John Dalton. Even though 2 centuries have passed, Dalton’s atomic theory continues to be valid in modern chemical thought.
2) All atoms of a given element are identical in mass and properties
3) Compounds are formed by a combination of two or more different kinds of atoms.
4) A chemical reaction is a rearrangement of atoms (Leon, n.d.).
3. D Mendeleev:
Mendeleev was the first to establish the concept of a periodic table based on atomic weights. This eventually became one of the most iconic symbols of science through the ages and is recognised by most persons regardless of their study of the subject itself (The Doc, 2014).
4. Eugene Goldstein:
The german physicist was the first to discover positively charged particles within an atom. He used a tube filled with hydrogen gas similar to Thompson’s tube and found out that the positive particle had equal and opposite charge of an electron and a mass of 1.66E-24 grams or one atomic mass unit. The positive particle was named the proton ("History of Chemistry," n.d.).
5. J.J.Thompson:
Thompson created a model of the atom in the form of a sphere of positive matter in where in electrons were positioned by electrostatic forces (Chemical Heritage Foundation, 2015).
6. E. Rutherford:
His most famous work is the gold foil experiment. He shot alpha atoms at a thin piece of gold foil and observed the positions on a circular surrounding wall it hit. According to previous knowledge, it was expected that all the particles would pass. However, some bounced to the sides while others returned back towards the Alpha atom stream.He was the first to discover an entity in at the center of the atoms called the nucleis. ("Ernest Rutherford," n.d.).
7. N Bohr:
Bohr was the first to explain how electrons can have stable orbits surrounding the nucleus through his proposition of the quantized shell model of the atom. Movement of the electrons was unstable as any charged particle travelling on a curved path emits electromagnetic radiation. Therefore electrons lose energy and spiral into the nucleus. To fix this problem Bohr changed the Rutherford model with the hypothesis that electrons moved in orbits of fixed size and energy. Depending on the size of an orbit, each electron has energy which decreases for smaller orbit (University of Oregon, n.d.).
8. Schrodinger:
According to Neil Bohr’s theory of an atom, electrons absorb and emit radiation of fixed wavelengths when moving between fixed orbits surrounding the nucleus. Assuming that matter (e.g., electrons) could be regarded as both particles and waves, in 1926 Erwin Schrödinger formulated a wave equation that accurately calculated the energy levels of electrons in atoms. (Dirac, n.d.).
- Democritus
2. J Dalton:
Even after Democritus’s suggestion of the existence of an atom, it took almost 2 millenia before the atom was established as a fundamental chemical object by John Dalton. Even though 2 centuries have passed, Dalton’s atomic theory continues to be valid in modern chemical thought.
- Dalton's Atomic Theory
2) All atoms of a given element are identical in mass and properties
3) Compounds are formed by a combination of two or more different kinds of atoms.
4) A chemical reaction is a rearrangement of atoms (Leon, n.d.).
3. D Mendeleev:
Mendeleev was the first to establish the concept of a periodic table based on atomic weights. This eventually became one of the most iconic symbols of science through the ages and is recognised by most persons regardless of their study of the subject itself (The Doc, 2014).
4. Eugene Goldstein:
The german physicist was the first to discover positively charged particles within an atom. He used a tube filled with hydrogen gas similar to Thompson’s tube and found out that the positive particle had equal and opposite charge of an electron and a mass of 1.66E-24 grams or one atomic mass unit. The positive particle was named the proton ("History of Chemistry," n.d.).
5. J.J.Thompson:
Thompson created a model of the atom in the form of a sphere of positive matter in where in electrons were positioned by electrostatic forces (Chemical Heritage Foundation, 2015).
6. E. Rutherford:
His most famous work is the gold foil experiment. He shot alpha atoms at a thin piece of gold foil and observed the positions on a circular surrounding wall it hit. According to previous knowledge, it was expected that all the particles would pass. However, some bounced to the sides while others returned back towards the Alpha atom stream.He was the first to discover an entity in at the center of the atoms called the nucleis. ("Ernest Rutherford," n.d.).
7. N Bohr:
Bohr was the first to explain how electrons can have stable orbits surrounding the nucleus through his proposition of the quantized shell model of the atom. Movement of the electrons was unstable as any charged particle travelling on a curved path emits electromagnetic radiation. Therefore electrons lose energy and spiral into the nucleus. To fix this problem Bohr changed the Rutherford model with the hypothesis that electrons moved in orbits of fixed size and energy. Depending on the size of an orbit, each electron has energy which decreases for smaller orbit (University of Oregon, n.d.).
8. Schrodinger:
According to Neil Bohr’s theory of an atom, electrons absorb and emit radiation of fixed wavelengths when moving between fixed orbits surrounding the nucleus. Assuming that matter (e.g., electrons) could be regarded as both particles and waves, in 1926 Erwin Schrödinger formulated a wave equation that accurately calculated the energy levels of electrons in atoms. (Dirac, n.d.).
REFERENCES
Berryman, S. (2010, August 25). Democritus. In Stanford University (Ed.), Stanford encyclopedia of philosophy (pp. 1-2). Retrieved August 23, 2016, from http://plato.stanford.edu/entries/democritus/
Chemical Heritage Foundation. (2015, July 22). Joseph john “j. j.” thomson. Retrieved August 23, 2016, from https://www.chemheritage.org/historical-profile/joseph-john-%E2%80%9Cj-j%E2%80%9D-thomson
Dirac, P. A.M. (n.d.). Erwin schrödinger - facts. Retrieved August 23, 2016, from https://www.nobelprize.org/nobel_prizes/physics/laureates/1933/schrodinger-facts.html
The Doc. (2014, September 1). Dmitri-mendeleev. Retrieved August 23, 2016, from http://www.famousscientists.org/dmitri-mendeleev/
Ernest rutherford. (n.d.). Retrieved August 23, 2016, from http://historyoftheatomictheory.weebly.com/ernest-rutherford.html
History of chemistry. (n.d.). Retrieved August 23, 2016, from http://www.columbia.edu/itc/chemistry/chem-c2507/navbar/chemhist.html
Leon, N. D. (n.d.). Dalton’s atomic theory. Retrieved August 23, 2016, from http://www.iun.edu/~cpanhd/C101webnotes/composition/dalton.html
University of Oregon. (n.d.). Bohr atomic model. Retrieved August 23, 2016, from http://abyss.uoregon.edu/~js/glossary/bohr_atom.html
Chemical Heritage Foundation. (2015, July 22). Joseph john “j. j.” thomson. Retrieved August 23, 2016, from https://www.chemheritage.org/historical-profile/joseph-john-%E2%80%9Cj-j%E2%80%9D-thomson
Dirac, P. A.M. (n.d.). Erwin schrödinger - facts. Retrieved August 23, 2016, from https://www.nobelprize.org/nobel_prizes/physics/laureates/1933/schrodinger-facts.html
The Doc. (2014, September 1). Dmitri-mendeleev. Retrieved August 23, 2016, from http://www.famousscientists.org/dmitri-mendeleev/
Ernest rutherford. (n.d.). Retrieved August 23, 2016, from http://historyoftheatomictheory.weebly.com/ernest-rutherford.html
History of chemistry. (n.d.). Retrieved August 23, 2016, from http://www.columbia.edu/itc/chemistry/chem-c2507/navbar/chemhist.html
Leon, N. D. (n.d.). Dalton’s atomic theory. Retrieved August 23, 2016, from http://www.iun.edu/~cpanhd/C101webnotes/composition/dalton.html
University of Oregon. (n.d.). Bohr atomic model. Retrieved August 23, 2016, from http://abyss.uoregon.edu/~js/glossary/bohr_atom.html