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Democritus wondered what would happen if you kept cutting an apple in half, you would eventually reach a point where you can’t cut anymore. He decided that Invisible particles make up all life on Earth. He named them Atomos which means ‘uncuttable’. His ideas ended up being forgotten for 2000 years.
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John Dalton brought back Democritus’s ideas and created the first atomic theory. The atomic theory Dalton developed consists of three ideas:
• All substances are made of atoms.
• All atoms of the same element are alike and have the same mass.
• Atoms join together to form compounds.
Dalton incorrectly thought that atoms are tiny solid particles of matter. He used solid wooden balls to model them. His models were too simple and didn’t show the subatomic particles. -
J. J. Thompson discovered the first subatomic particle. He named them electrons. He thought that atoms were like plum pudding with plums (or electrons in this case) spread throughout it. He also thought that the empty space inside the atom was positively charged. He knew that electrons were negatively charged.
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Ernest Rutherford discovered many things about the Atom. He discovered the Nucleus, the Protons and Atoms are not solid. Later, he discovered that the nucleus contains positively charged particles. He named the positive particles protons. He predicted the existence of Nutrons but could prove their existence. He also thought that electrons orbit the Nucleus at random.
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Niels Bohr thought that electrons are located at fixed distances away from the Nucleus.
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James Chadwick discovered the Neutron
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The electron cloud is the area where people thought electrons are likely to be.