History of the Atom Flashcards
What does Democritus do?
Democritus proposed the first atomic theory which states that all atoms are small, hard, indivisible and indestructible particles made of a single material formed into different shapes and sizes.
What does John Dalton do?
In 1803, proposed an Atomic Theory which states:
All substances are made of atoms; atoms are small particles that cannot be created, divided, or destroyed.
Atoms of the same element are exactly alike, and atoms of different elements are different
Atoms join with other atoms to make new substances
John Dalton Calculated the atomic weights of many various elements
What does J.J. Thomson do
Proved that an atom can be divided into smaller parts
While experimenting with cathode-ray tubes, discovered corpuscles, which were later called electrons
Thomson was experimenting by applying high voltages to gases at low temperatures.
Thomson did experiments on the beams of particles.
The particles were attracted to a positive charge, showing they must be negatively charged themselves.
These electrons must have come from inside the atoms in the tube.
Dalton’s idea that atoms could not be divided or split had to be revised.
Stated that the atom is neutral.
In 1897, proposed the Plum Pudding Model which states that atoms mostly consist of positively charged material with negatively charged particles (electrons) located throughout the positive material.
He imagined the electrons as the bits of plum in a plum pudding.
What did Ernest Rutherford do
In 1909, performed the Gold Foil Experiment and suggested the following characteristics of the atom:
It consists of a small core, or nucleus, that contains most of the mass of the atom
This nucleus is made up of particles called protons, which have a positive charge
The protons are surrounded by negatively charged electrons, but most of the atom is actually empty space
Describe and explain the Gold foil experiment
Experiment was carried out by his assistants Geiger and Marsden
A beam of alpha particles (dense positively charged particles) was aimed at very thin gold foil and their passage through the foil detected.
The scientists expected the alpha particles to pass through the foil with their diffuse cloud of positive charge but something else also happened.
Some of the alpha particles emerged from the foil at different angles and some even came straight back.
The scientists realised that the positively charged alpha particles were being repelled and deflected by a tiny concentration of positive charge in the atom.
As a result of this experiment, the plum pudding model was replaced by the nuclear model of the atom.
How did the gold foil experiment disprove thomson’s plum pudding model
Rutherford suggested thomson’s atomic model was not possible.
The positive charge must be concentrated at a tiny spot in the centre of the atom. Otherwise the large positive particles fired at the foil could never be repelled back towards their source.
It was proposed that the electrons must be orbiting the nucleus, which contains dense positively charged electrons.
State two ways in which rutherford changed thomsons model of the atom
A positive charge concentrated into very small volume at
centre of atom (nucleus),
electrons orbit nucleus
Rutherford’s nuclear model of the atom
https://study.com/cimages/multimages/16/rutherford_atom_4.jpg
What did Niels Bohr do?
In 1913, proposed the Bohr Model, which suggests that electrons travel around the nucleus of an atom in orbits or definite paths. Additionally, the electrons can jump from a path in one level to a path in another level (depending on their energy)
He noticed that the light given out when atoms were heated only had specific amounts of energy
Bohr’s model of the atom
https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcTEqlr0jbt83COt1a5jf4-5kn3gFYusxh7avnAbAAuiUMo5RCPe1j2w3BEJpAXDUw0-zHI&usqp=CAU
excited electron
What did James Chadwick do
Realized that the atomic mass of most elements was double the number of protons this led to the discovery of the neutron in 1932
1932, did an experiment that could only be explained by the existence of neutrons
Draw the diagram which shows the plum pudding model of the atom
https://upload.wikimedia.org/wikipedia/commons/thumb/2/26/Plum_pudding_model.svg/800px-Plum_pudding_model.svg.png
Draw the diagram which shows the model of the atom developed from the alpha particle scattering experiment
https://thehistoryoftheatomicmodel.weebly.com/uploads/2/5/4/7/25471775/3901756.jpg
Draw the model of the atom resulting from Bohr’s work
https://cdn.britannica.com/09/149209-050-57443291/Bohr-model-nitrogen-atom.jpg
Chadwick’s experimental work on the atom led to a better understanding of isotopes.
Explain how his work led to this understanding.
Chadwick provided the evidence to show the existence of
neutrons
This was necessary because isotopes have the same number of protons but with different number of neutrons