-
450 BCE
Earth, Water, Air, & Fire: Aristotle, ~450 BCE
Points
1. Aristotle thought atoms were non-existent.
2. Aristotle believed that matter was made up of four substances (earth, fire, water and air).
3. The four substances were believed to have four specific qualities, which were dry, hot, wet, and cold. -
Period: 450 BCE to
Development Of The Atomic Theory
-
400 BCE
An Indivisible Particle - The Atom: Democritus, ~400 BCE
Points
1. Democritus suggested that all matter is made out of atoms.
2. He thought that matter can be separated into smaller pieces, until a sole indivisible particle is reached. This indivisible particle was named the atom, which means "cannot be cut."
3. Democritus suggested, without gathering any scientific evidence, that atoms vary in sizes, are always in motion, and are separated by empty spaces. -
The Billiard Ball Model: John Dalton, 1807
Points
1. Dalton suggested that all matter is made out of minuscule, unbreakable particles called atoms.
2. He proposed that all atoms in a specific element are identical, and atoms in different elements are nonidentical.
3. Also, he proposed that atoms can never be created or destroyed, but they can be rearranged during chemical reactions to form new substances. -
Plum Pudding Model - The Electron: J.J. Thomson, 1897
Points
1. J.J. Thomson speculated that atoms contain negatively charged particles, called electrons.
2. Thomson postulated that negatively charged particles, electrons, are uniformly distributed throughout the atom.
3. He theorized that since atoms are neutral, the rest of an atom (apart from the electrons) would be a positively charged sphere. -
The Gold Foil Experiment - The Nucleus And The Proton: Ernest Rutherford, 1909
Points
1. In Rutherford's test of Thomson's atomic theory, he concluded that there is a positive charge at the centre of the atom (the nucleus). Which contains the majority of the atom's mass even though it is very small.
2. Rutherford's result concluded that the majority of an atom is empty space.
3. Also, he concluded that the nucleus is surrounded by negatively charged electrons.
Fun Fact: Ernest Rutherford discovered the proton in 1920. -
Planetary Model (Bohr-Rutherford Model): Niels Bohr, 1913
Points
1. Niels Bohr theorized that electrons orbit the nucleus similar to how planets orbit the sun.
2. Also, he concluded that every electron has a certain amount of energy and the further an electron is from the nucleus the more the energy it contains.
3. Bohr also proposed that each orbit can hold a certain amount of electrons. The first orbit can hold a total of 2 electrons, and every orbit after the first one can hold a total of 8 electrons. -
Planetary Model - The Neutron: James Chadwick, 1932
Points
1. Chadwick suggested that an atom is an empty sphere with a minuscule dense nucleus located at the centre where positively charged protons and neutral neutrons are located.
2. James Chadwick also theorized that negatively charged particles, electrons, circle rapidly in the empty space around the nucleus.
3. He also concluded that a neutral atom has the same number of protons and electrons.
