Theories and Important people of Atoms

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Theories and Important people of Atoms

More detailed history of atomic models

1. Dalton

Atomic Theory

- Elements are made up of unique atoms.

- Compounds have constant ratio of atoms.
  -->  Law of definite proportions

- Atoms are neither created nor destroyed in chemical reactions.
 -->  Law of mass conservation

- Atom model : the shape of a ball that no longer splits.

2. Thomson

Cathode ray experiment

- Atom model : plum Pudding Model

- An atom is a spherical mass containing sporadic (-) electric charges and (+) electric charges.

3. Rutherford 

Gold foil experiment

- 1. Crash α particles into thin gold foil
  2. He found that very few α particles were moving in different directions.
  3. Found that most of the atoms are empty spaces, and (+) charges are concentrated in a fraction of         the core of the atom.
  4. The electron is very small, circling around the nucleus.

4. Bohr 

Propose 'solar system' model of atom and make Hydrogen Atom Model

- Electrons in the hydrogen atom move around the nucleus only in certain allowed circular orbits

- Track with constant energy status is denoted as energy level

- The energy level is determined by the value of n.
  n=1 : ground state, n=∞: the state in which electrons are separated from the atom

- Energy of an electron
  En =  -2.178 * 10 ^-18 / n^2 Joules (n: principal quantum number)

- When an atom absorbs energy, the electron moves further away from the nucleus into a higher energy orbit.

-When an atom emits energy, the electron moves into a low energy orbit close to the nucleus.