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420 BCE
Democritus
Democritus found that all things were made up of atoms. His research added to our knowledge that atoms made up of the same type have the same properties. He discovered this by
observing that if you manipulated the same items the same way, you’d get the same results. -
John Dalton
Dalton did not create a new model but he added to our knowledge that atoms represent the properties of an element. To find this out he used the Law of Conservation of Mass and found out that atoms of the same element have the same mass by exploring mass ratios -
JJ Tomson - England
JJ Tomson discovered electrons in 1890. He created a model called the Plum Pudding Model. This model showed that there was an even distribution of negative charges throughout a positive atom. This added to our knowledge that there are smaller particles than an atom. He did this by using a cathode tube to isolate and grab the electron. He then weighed the electron and found out that it weighed less than hydrogen. -
Robert Millikan - America
In 1909 Robert Milikan found out the charge and the size of electrons. Millikan found that the subatomic particle Thomson had found in the 1990s was actually negatively charged. This addition to our knowledge was a very significant discovery. To discover that the subatomic particle was negative, Milikan used the effect that two charged plates had on charged oil to measure how much an electron weighs. -
Ernest Rutherford - England
In 1911, Ernest Rutherford discovered the nucleus in an atom. Rutherford found that an atom is an empty space with a nucleus located in the center of the atom. We finally had the structure of an atom after 100s of years. To find the nucleus Rutherford fired Alpha particles at a thin gold foil. Most of the particles passed through the gold because most of an atom is empty space. A few bounced off of the nuclei of the gold atoms. -
Niels Bohr - Denmark
In 1919 Niels Bohr discovered that an atom has a dense and positive nucleus with electrons that have energy levels orbiting around it. His model demonstrated electrons in energy shells. This expanded our knowledge of atoms by telling us what area subatomic particles are.. To find this out Bohr used the way that different atoms release light when they are excited to show that different atoms absorb different amounts of energy. -
Modern Atom
The modern atom is a mixture of all the previous scientists' research put together. Added knowledge is that electrons sit in an electron cloud rather than orbits.
