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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Ancient Greek philosopher who thought that matter was made of small indivisible particles. He name them “atoms” which means indivisible in Greek
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,
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
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
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
Positive chargefound in the nucleusweighs 1 amu (atomic mass unit)
Negative chargefound in the electron cloud surrounding the nucleustakes almost 2000 of them to weigh as much as one proton or neutron
No charge (neutral)found in the nucleusweight one amu
Number of protonsunique to each element
Number of protons and neutrons combined
Atoms of the same element with a different number of neutrons