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450 BCE
The start of matter
Empedocles was a Greek scholar that proposed that matter was composed of 4 elements, earth, fire, water and air. Unlike must philosophers from his time he would use experiments to determine his ideas. He demonstrated that even though air is invisible it must contain something because it takes up space. -
400 BCE
Atoms
Democritus, another Greek philosopher, suggested that matter is made of tiny particles that cant be broken any smaller. He called the particles atoms, after the Greek word "atomos" which mean invisible. This means that elements were made of different kinds of atoms which was revolutionary at the time. Democritus's ideas weren't widely accepted because of Socrates, a big figure at the time. -
350 BCE
Influence matters
The philosopher Aristotle agreed with Empedocles "4 element" model despite the recent "Atomic" model. Aristotle's influence was so strong and his writings read by so many that the "4 element" model was accepted for more than 200 years. -
Period: 500 to
Lead to Gold
During this time alchemists thought that you could make gold from cheap materials, just like a plant. They did experiments trying to make gold out of metals like lead. They ended up making symbols for substances we now know are elements and compounds. They also invented new tools that we still use to this day. Though they did all of this they still believed the "4 element" model! -
Finally Change
Robert Boyle an English scientist was one of the first to make change on the "4 element" model. He didn't believe it and made a new definition of the word element, "I mean by element, two mitigated bodies". This became the modern definition of the word element, a pure substance that can't be broken down. -
Oxygen, Element or Compound?
Joseph Priestly was the first person to isolate oxygen but he did't know it was a element. Antoine Lavoisier soon found this out. Antoine also found out that air was a mixture of at least two gases, one of which is oxygen. Meanwhile, Henry Cavendish was mixing a metal with acid and found a gas that was lighter than oxygen, he didn't know he made hydrogen. He discovered that his gas would burn in Priestly's oxygen, making water. Until then water was an element. -
Element or Non Element?
By this time the two models were put together and it was known that matter was made of elements. An English chemist John Dalton published a theory of why elements are different from non elements. -Matter is made of atoms, that are to small to see. -Each element has different atoms and particle masses. -Compounds are formed by two or more elements. -Atoms can't be destroyed, made or divided during in chemical changes. -
Ions
Matter can create positive and negative charges, this was one thing Dalton's method didn't cover. Since that method didn't explain that, a new one was developed showing that tiny negative charge particles can break off and move for one atom to another. In 1831, Michael Faraday found that electric current could cause chemical changes in some compounds and solutions.The atoms could gain electric charges and form charged atoms, called Ions. This became the modified version of Dalton's model. -
Ions Part .2
- Matter must contain positive and negative charges.
- Opposite charges attract and two of the same charges repel.
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Electrons and Protons P.2
Nagaota, a Japanese scientist, modeled the atom with a large positive sphere surrounded by a sphere of negative electrons -
Electrons and Protons
J.J Thomson further adapted the atomic method, to explain his discovery of a light negative particle, called electrons. He also found much heavier positive particles(later found to be protons). This new model was called the "raisinbun" model. -Atoms contain particles called electrons. -Electrons have small masses and negative charges -The rest of the atom is sphere of a positive charge -The electrons stay in the sphere, so that other atoms are either neutral or uncharged. -
Nucleus
Ernst Rutherford wanted to test Thomson's and Nagaoka's models. He aimed a positive alpha charges (positively charged particles smaller than most atoms) at a gold sheet of foil. He predicted that the particles would pass through. Most did but some bounced back. To explain the positive alpha charges he had to come up with a new method. -An atom has a tiny, dense, positive core called the nucleus. -The nucleus is surrounded by mostly empty space with fats moving negative electrons moving around.
