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450 BCE
The Four Elements
Who: Greek scholar Empedocles
His Theory: Empedocles believed that matter was made up of the four elements but in unequal proportions to create different substances. (ex. volcanic rocks could be two parts fire but only one part air.)
Empedocles's theory was checked experimentally. He demonstrated that air can't just be "nothing" but that air is a form of matter. -
400 BCE
The atomic model
Who: Democritus (greek)
His theory: He believed that all matter was made up of tiny particles that could not be broken down in any way. He named these particles "atoms". In the atomic model, atoms were said to be in constant motion, different sizes (different regular geometric shapes), and separated by empty spaces.
This theory was not accepted in the world since a more influential man (Socrates) did not agree with it. -
350 BCE
Belief of the Four Elements
who: Greek philosopher Aristotle
Most recent theory: At this time, the most recent theory was the atomic model
His Theory: Aristotle also believed that matter was made up of the four elements. He did lots of writing and research on this theory. So many people read his pieces that the four-element theory was accepted for another 2000 years. -
Period: 500 to
Continuation of the Four Elements
Who: alchemists
Recent Theory: The Four-element model was still an accepted model.
Theory: The alchemists believed that they could take metal (iron and lead) and turn it into gold. For centuries they performed experiments in an attempt to turn metal into gold. They created chemical symbols for substances that today are known as elements and compounds. The alchemists also created many laboratory tools that are still used today. In the end, they never turned any metal into gold. -
Element
who: Robert Boyle (English scientist)
Most recent theory: The four-element model, which he did not believe in.
His theory: Robert created a new meaning for the word element. The improved definition of the word element was a pure substance that can not be chemically broken down into simpler substances. Robert Boyle also believed that air was a mixture, not an element. -
Hydrogen + Oxygen = Water
Who: Joseph Priestley, Antoine Lavoisier, Henry Cavendish Recent Theory: New definition of the word element (1650).
New Theory: Joseph Priestley was the first to recognize oxygen scientifically. But what he didn't know was that oxygen is an element, Lavoisier was the one to discover this. He concluded that air is a mixture of 2 gases, one of which is oxygen. Meanwhile, Henry created a gas not knowing it was hydrogen. What he did know was his gas would burn in oxygen, producing water. -
Period: to
improved atomic model (1800s)
who: Micheal Faraway
Previous: Daltons' atomic model didn't explain how you can get a shock on a dry day.
Theory: Micheal created a new model that introduced tiny negatively charged particles, they can be separated from their atoms and moved to others. He found atoms can gain electric charges and form ions (charged atoms). In his updated version of Dalton's model:
-Matter must contain positive & negative charges
-Opposite charges attract & like charges repel
-Atoms combine to form molecules. -
New Atomic Model (atoms are solid spheres in this model)
who: John Dalton
Previous: matter was made of elements
Theory:Dalton created an atomic model that explains chemical charges: atoms combine & molecules separate during chemical reactions.
Theory states:
-all matter is made of atoms
-each element has its own kind of atom and particular mass
-compounds are made when atoms of different elements link to form molecules
-Atoms can't be created, destroyed, or subdivided in chemical changes
It explains why elements differ from each other & non-elements. -
The "Raisin-bun" model
Who: J.J Thompson, Nagaoka
Theory: J.J revised the atomic model, in this model he explains his discovery of electrons (light negative particles) & his experiments with beams of heavier particles (protons).
-Atoms contain particles called electrons
-Electrons have a small mass & negative charge
-The rest of the atom is a sphere of positive charge
-Electrons are in this sphere so that the resulting atoms are neutral or uncharged
Nagaoka modeled the atom as a + sphere with embedded electrons -
The nuclear model
who: Ernest Rutherford
Previous: The atomic model
Experiment: Rutherford designed an experiment to test Thompson's & Nagoka's model. He aimed a type of radiation called alpha particles (positively charged particles) at a thin sheet of gold. His hypothesis was based on the raisin-bun model, he predicted that the particles would pass through the thin sheet, which most did except a small number of which bounced back. The only way he could explain it was to design a new model, the nuclear model. -
continuation of Nuclear model
continuation...
In Ernest Rutherford's nuclear model he states:
-an atom has a small, dense, positive core hat contains protons called the nucleus (this is was deflected the alpha particles)
-The nucleus is surrounded mostly by empty space, containing fast-moving negative electrons (the alpha particles passed through this
simply)
