Collect the information of historical development of atomic theory
Answers
According to the Dalton's atomic theory, atom was indivisible and indestructible. The discovery of two fundamental particles (electrons and protons) inside the atom, led to the failure of this aspect of Dalton's theory. .
To know the arrangement of electrons and protons with in an atom many scientists proposed various atomic models.
1. Thomson's Model of an atom :
Thomson's model of an atom was compared to Christmas pudding. The electrons in a sphere of positive change were like currants (dry fruits) in a spherical chritmas pudding.
It can also be compared to a water melon, in which the positive change in an atom is spread all over like the red edible part, while the electrons studded in the +vely changed sphere, like seeds in the water melon.
The following are the postulates of this theory
(i) Electrons are embedded in the sphere of positive change.
(ii) Mass of an atom is due to these electrons.
(iii) The -ve and +ve charge balance each other. Therefore, atom as a whole is neutral.
2. Rutherford's Model of an atom :
The postulates of this theory are
(i) Most of the space inside the atom is empty because most of the d-particles passed through the gold foil without getting deflected in an alpha - ray scattering experiment.
(ii) Very few particles were deflected from their path, indicating that the positive charge of the atom occupies a little space.
(iii) A very small fraction of a - particles were deflected by 180 (rebound), indicating that all the +ve charge and mass of an atom were concentrated in a very small volume with in atom called the nucleus. Nearly, whole mass of the atom reside in the nucleus.
(iv) The size of the nucleus (10−1510−15m) is very small as compared to the size of the > atom (10−1010−10m).
Limitations of Rutherford's Model :
(i) Any charged particle when accelerated is expected to radiate energy. To remain in a circular orbit, the electron would meed to undergo acceleration. .-. it would radiate energy.
Thus, the revolving e−e− would lose energy and finally fall into the nucleus. If this were so, the atom should be highly unstanle. The matter would not exist, but we know that atoms are quite stable.
(ii) It could not explain the distribution of electrons in the extra nucleus portion of the atom.
Answer:The idea behind the "atom" goes back to the Ancient Greek society, where scientists believed that all matter was made of smaller, more fundamental particles called elements. They called these particles atoms, meaning "not divisible." Then came the chemists and physicists of the 16th and 17th centuries who discovered various formulae of various salts and water, hence discovering the idea of a molecule.
Then, in 1766 was born a man named John Dalton born in England. He is known as the father of atomic theory because he is the one who made it quantitative, meaning he discovered many masses of various elements and, in relation, discovered the different proportions which molecules are formed in (i.e. for every water molecule, one atom of oxygen and two molecules of hydrogen are needed). He also discovered the noble, or inert gases, and their failure to react with other substances. In 1869 a Russian chemist, best known for his development of the periodic law of the properties of the chemical elements
Explanation:In the early 1900s a Japanese scientist named H. Nagaoka designed an atom model as a large sphere surrounded by a ring of negatively charged electrons. Also, during the early 1900s (1898-1907) a physicist named Ernest Rutherford worked on experiments to test current atom models.
In the 1700’s, Antoine Lavoiser wrote the first extensive list of elements and categorized them into metals and non-metals . Johann Wolfgang Döbereiner and Alexandre-Emile Béguyer de Chancourtois also tried to classify the elements in the mid 1800’s but were not extremely successful.
In 1898, Marie Curie (Polish physicist) and Pierre Curie (French physicist) were one of the first scientists to isolate radium and polonium from pitchblende (uraninite). Henri Becquerel received a Nobel Prize for his work, finding radioactivity in uranium. Wilhelm Konrad Rontgen also received a Nobel Prize for discovering the X-ray.
1803 John Dalton British chemist and physicist John Dalton theorised that matter is composed of spherical atoms (that are in motion) of different weights and are combined in ratios by weight. 1896 Wilhelm Rontgen Discovered that certain chemicals glowed when exposed to cathode rays
With the help of Geiger he found the number of alpha particles emitted per second by a gram of radium. He was also able to confirm that alpha particles cause a faint but discrete flash when striking luminescent zinc sulfide screen. These great accomplishments are all overshadowed by Rutherford's famous Gold Foil experiment which revolutionized the atomic model.
One of the next most recognized people involved in the progression of atomic theory was J.J. Thompson. Thompson had researched the work of William Crookes whose research concluded that cathode rays were deflected by magnetic fields. Thompson elaborated on this conclusion and found that cathode rays were also deflected by an electric field. With much experimentation Thompson theorized that although the atom was made up of small particles it was not the same indestructible model proposed by Dalton. A man named Milikin determined the mass of an electron to be 0 amu and the relative charge to be negative 1.