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450 BCE
around 450 BCE
A Greek philosopher named Aristotle rejected the idea of the atom. He supported an earlier idea that all matter was made up of four basic substances, earth, water, air, and fire, he thought these substances had four specific qualities, dry, wet, cold, and hot. Aristotle's theory on the structure of matter was believed for nearly 2000 years. -
Period: 450 BCE to
Changing human understanding of matter
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400 BCE
Around 400 BCE
The Greek Philosopher, Democritus had an idea that all matter can be divided into small pieces until a single invisible particle is reached. He named this particle the atom, atom means "cannot be cut". Without any experimental evidence he proposed that all atoms are of different sizes, always in constant motion, and separated by small empty spaces. These are now all part of the particle theory of matter. -
Around 1807
An English scientist and teacher named John Dalton, he revived the theory of democritus that explained that Indivisible atom. Which proposed that all matter is made up of tiny, Indivisible particles called atoms. All atoms of an element are identical. Atoms of different elements are different. Atoms are rearranged to form new substances in chemical reactions, but they are never created or destroyed. -
Around 1807
Dalton's model is known as the billiard ball model, His model could explain many properties of matter. However the billiard ball could not explain why some objects attract each other and why others repel each other. The explanation of rubbing a balloon on your hair to create static energy was explained over 100 years later. -
Around 1897
In 1897 a man named J.J Thomson that very small negatively charged particles could be transmitted through very hot materials. These particles were specifically attracted to the positive end of a circuit. The positive and negative charges were known to be attracted to one another, so Thomson concluded that the particles were negatively charged. These particles were later examined further and named electrons. -
1897- J.J Thomson's Theory
Thomson theorized that all atoms have negatively charged electrons and since atoms are negatively charged the rest of the atoms is a positively charged sphere. Also that negatively charged atoms are distributed evenly throughout the atom. -
Around 1909 - Rutherford's prediction
A man by the name of Ernest Rutherford was a physical scientist who was supervising an experiment to Thomson's model of the atom. He predicted that if positive and negative charges were distributed throughout atoms, then tiny positively charged particles shot at a thin piece of gold foil would pass through. He also said that some particles might be slowed down or deflected at small angles when they were shot. -
Around 1909 - Rutherford's results
When the experiment happened most of the particles passed through the foil but some were deflected at very large angles like something was blocking them from going through. Rutherford then concluded that some of the particles had a collision with a small, concentrated, positively charged central mass inside the atom. He concluded that the center of the atom is called the nucleus, which has a positive energy and contains most of the atom's mass. The nucleus made the deflection happen.