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History of the Atom From Democritus to Bohr. Democritus of Abdera Greek 4 th century BC. Democritus is known as the "Laughing Philosopher“because of his.

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Presentation on theme: "History of the Atom From Democritus to Bohr. Democritus of Abdera Greek 4 th century BC. Democritus is known as the "Laughing Philosopher“because of his."— Presentation transcript:

1 History of the Atom From Democritus to Bohr

2 Democritus of Abdera Greek 4 th century BC. Democritus is known as the "Laughing Philosopher“because of his joyous spirit. He was a big man (relatively speaking) and enjoyed life tremendously. He also was very widely traveled.

3 All matter is composed of atoms, which are bits of matter too small to be seen. These atoms CANNOT be further split into smaller portions. There is a void, which is empty space between atoms. Atoms are completely solid. Atoms are homogeneous, with no internal structure. Atoms are different in... »1)...their sizes »2)...their shapes. »3)...their weight.

4 John Dalton English physicist Early 1800’s The atom is a solid mass.

5 1) chemical elements are made of atoms 2) the atoms of an element are identical in their masses 3) atoms of different elements have different masses 4) atoms only combine in small, whole number ratios such as 1:1, 1:2, 2:3 and so on. This is called the THE LAW OF MULTIPLE PROPORTIONS. 5) ENERGY can neither be created nor destroyed. Atoms store energy (protons, neutrons, electrons) 6) Elements in a compound will always combine in fixed ratios.

6 J.J.Thomson English Physicist 1856-1940 Experimented with cathode rays Pictured the atom as “Plum Pudding”

7 Discovered that cathode rays were made of negatively charged particles that had a mass 1000 times smaller than Hydrogen. Called particles corpuscles. (now called electrons) Eluded to the idea that if there are negative particles in matter, there must also be positive particles. Atomic theory; By the way, this is often referred to as Thomson's "plum pudding model," where the pudding represents the sphere of positive electricity and the bits of plum scattered in the pudding are the electrons.

8 Ernst Rutherford Enjoyed studying science for the sole purpose of learning new things. 1898-1911 studied alpha-particles Developed the Solar System approach to the structure of the atom.

9 Most of the mass of an atom was located in the nucleus. When bombarding gold foil with alpha particles, his team discovered these things; 1.The nucleus is so small that the alpha particles will go right through. 2.Some will go near gold nuclei and be deflected. 3.Very few will ever hit a nucleus “head-on”. 4.The positive charge of the nucleus repels the alpha particles.

10 Professor James Chadwick English Physicist 1932, confirmed the existence of the neutron.

11 Neils Bohr Developed new more modern theory of the atom

12 Bohr’s Atomic theory 1) There is a nucleus (this was Rutherford's discovery). 2) The electrons move about the nucleus in "stationary states" which are stable, that is, NOT radiating energy. 3) When an electron moves from one state to another, the energy lost or gained is done so ONLY in very specific amounts of energy, not just any old amount. 4) Each line in a spectrum is produced when an electron moves from one stationary state to another.

13 Electrons rotate about the nucleus in "orbitals," like the planets rotating around the sun. Electrons normally exist only in well defined regions, called quantum energy levels, around the atom. These energy levels surround the atom like a "cloud." Bohr Model of the Atom

14 Atomic Models


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