Democritus 400 bc
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Democritus 400 BC. Ancient Greek philosopher who thought that matter was made of small indivisible particles. He name them “atoms” which means indivisible in Greek. John Dalton 1830. Agreed with Democritus model of the atom and Added to Democritus idea.

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Democritus 400 BC

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Democritus400 BC


Ancient Greek philosopher who thought that matter was made of small indivisible particles. He name them “atoms” which means indivisible in Greek


John Dalton1830


Agreed with Democritus model of the atom and Added to Democritus idea


Agreed with Democritus that matter was made of small indivisible particles. His model was the atom was tiny solid spheres. Each element had a different size sphere


He created an atomic theory that consisted of 4 parts1) Chemical elements are made up of atoms. 2) The atoms of an element are identical in their masses. (Be sure students understand that this was shown to be false with the discovery of isotopes.) 3) Atoms of different elements have different masses. 4) Atoms only combine in small, whole number ratios such as 1:1, 1:2,


J.J. Thomson1897


Found that atoms are divisible by discovering the electrons


Used a cathode ray tube to discover electrons (negative particles)Thought the negative particles were mixed in the positive charge like raisins in plum pudding


Ernest Rutherford1908


Was a former student of J.J Thomsondisproved his idea of the plum pudding model


Thought that the atom is mostly empty space.(football stadium model)discovered the nucleus by doing an experiment with gold foil


Niels Bohr1913


Worked under J.J. Thomson and Ernest Rutherford to improve the model of the atom


Thought that electrons orbit the nucleus like planets orbit the sun. We still draw atoms like this today.


Electron Cloud Theory1920’s


States that electrons don’t stay in fixed orbits. They can move from one energy level to another. This model is more like a ceiling fan. You know were the blades are but you can pinpoint one blade


First energy level can have 2 electronssecond can have 8third can have up to 18 (but it prefers 8) and the 4th can have up to 32


Protons


Positive chargefound in the nucleusweighs 1 amu (atomic mass unit)


Electron


Negative chargefound in the electron cloud surrounding the nucleustakes almost 2000 of them to weigh as much as one proton or neutron


Neutron


No charge (neutral)found in the nucleusweight one amu


Atomic number


Number of protonsunique to each element


Atomic mass


Number of protons and neutrons combined


Isotope


Atoms of the same element with a different number of neutrons


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