the atom chemistry history Flashcards
What is Dalton’s atomic theory?
All matter is made of very small indivisible particles – ‘atoms’…..
……Atoms of a given element are identical…….
…….Atoms cannot be created or destroyed……
Atoms of different elements combine in constant ratios to form compounds.
Atoms are rearranged in reactions.
What is the law of conservation of mass?
aroms can’t be created nor destroyes
the law of constant composition
elements combine in fixed ratios
what happens when an electric current passes through gas
it causes it to glow
Discuss Crookes’ experiment with a discharge tube and his conclusions?
he managed to prove that cathod rays were real even thought they were invisible by using electricity and vacuum tubes. he saw that the glass started to glow and the shadow of the cross appeared
Who showed that cathode rays are negatively charged? How did they do this?
J.J Thompson. He placed an electromagnet outside the glass tube and adjusted the strength of the magnetic field, he discovered that this deflected the electrons.
Who came up with the name ‘electron’?
J.J Thompson
Describe Robert Millikan’s experiment and his conclusions
-Droplets of oil between two charged metal plates.
-Ionised the air between the plates to form electrons.
-As the oil droplets fell due to gravity they picked up these electrons and became negatively charged.
-Placing a positive charge on the top plate he observed that the negatively charged droplet ignored gravity and was attracted upwards.
-He adjusted the charge on the plate until the oil drop was suspended in mid air
Describe Thompson’s Plum Pudding model.
Thomson said the atom was a sphere of positive charge with negative electrons embedded at random.
Describe Rutherford’s gold foil experiment
Bombarded a piece of gold foil with alpha particles (positively charged particles)
Detected the alpha particles using a fluorescent screen
Discovered that some of the alpha particles were reflected at different angles
what were rutherford’s conclusions
Most a particles travel through the foil undeflected –> the atom is mostly empty space
some a particles are deflected by small angles –> the nucleus is positively charged and so is the a parcticle
ocasionally an a particletravles back from the foil –> the nucleus carries most of the atom’s mass
What is Bohr’s model of the atom?
Electrons orbit the nucleus in “shells”
These shells have a definite/characteristic energy so they are called energy shells.
What did Chadwick discover? How did he do this?
he discovered neutrons.
-Bombarded beryllium with alpha particles.
-Saw that they knocked neutrons particles out of the nucleus of the beryllium.
-These particles then knocked protons out of the wax which were detected.
-These particles had roughly the same mass as the proton and had no charge so he called them neutrons.
Define atomic number.
The number of protons in the
nucleus of an atom of an element.
Define mass number.
The sum of protons and neutrons in the nucleus of an atom of an element
