History Of The Atom Flashcards
What is a atom
The smallest part of an element which still has the properties of that element
What is an Element
substance that cannot be broken down into anything simpler by chemical means
Matter
Anything which takes up space and has mass
What did the Greek philosophers propose
Matter was composed of small particles, these particles were so small they couldn’t be broken down into smaller particles (indivisible)
What did John Dalton develop
John Dalton developed the atomic theory
What is the atomic theory
All matter is made up of tiny indivisible particles called atoms that can be neither created nor destroyed. Atoms of the same element have identical atomic mass.
Who conducted the first experiments on cathode rays
William crookes
What are the properties of cathode rays
From William crooked experiments
Cathode rays travel in straight lines (sharp shadow)
Cathode rays cause glass to fluoresce when they strike it
Cathode rays have enough energy to move a paddle wheel
Who discovered electrons
JJ Thomson
What did JJ Thompson discover (in relation to the electron)
The charge to mass ratio
Discovered electrons are negatively charged
What model did JJ Thomson propose
The plum pudding model
Who discovered the exact charge of an electron
Robert Milikan
What experiment did Robert Milikan do to determine the exact charge of an electron ?
Oil droplet experiment
Who discovered the nucleus
Ernest Rutherford
Describe the golf foil experiment
Thin beam of alpha particles from a lead box with a sample of radium
Gold foil that acted as a thin layer of atoms
Detector screen
Very unexpected results
What model did Rutherford propose
Nuclear model
Who discovered neutrons?
James Chadwick
How did James Chadwick discover neutrons
By bombarding a beryllium sample with alpha particles, the neutrons were released at a detector / counter for protons
What is the atomic mass of an electron
1/1840
What are cathode rays
They are an electrical current coming from the negative end of a power supply
What are alpha particles
Positivity charged particles from a radioactive source
What was William Crookes investigating in the cathode ray expeirment
Investigate what happens when an electric current is passed through a gas tube containing air at low pressure (vacuum tube)
Describe the cathode ray experiment done by crookes
Cathode rays came from the cathode end of a power source. He showed the existence of this radiation
What was JJ Thompson investigating in his cathode ray expeirment
Investigated if the cathode rays discovered by crooked consisted of charged particles
Describe the cathode ray expeirment done by JJ Thompson
Obtained a narrow beam of cathode rays by passing them through a small hole in the anode.
If there was no charge on the magnetic plates the beam passed in a straight line.
But since the cathode rays were attracted so the positive plate, he concluded they consisted of negatively charged particles
Describe Thomsons plum pudding model
An atom is a sphere is positive charge. Electrons are embedded in the sphere at random. No evidence to prove
Describe the oil drop experiment by Robert Millikan
Sprayed tiny droplets of oil between two charged metal plates.
Ionised air( molecules in air lost electrons). The oil drops picked up the electrons. The oils droplets became attracted to the positive plate. Adjusted charge until stationary
Describe the expected results of the Gold foil by Ernest Rutherford
Based on Thomson’s plum pudding model, he predicted most of the atoms would pass straight through the gold foil. The positive charge would be too weak to affect the electrons
Explain the expected results of the gold foil experiment
Based on the plum pudding model by JJ Thompson, he predicted most of the atoms would pass straight through the gold foil. The positive charge would be too weak to affect the electrons
Describe the actual results of the gold foil experiment
While most of the alpha particles pass straight through the gold foil, a few alpha particles were deflected more than 90 degrees, and even smaller amount were deflected along the path they came from
What conclusion did Ernest Rutherford derive from the results
The positive charge must be localised over a tiny volume of the atom, which contains most of the atoms mass.
Since most of the alpha particles pass straight through , the atoms must be mostly made up of empty space
Describe the nuclear model
Positive nucleus with an electron cloud
