Chapter 2 - The Atom Flashcards
(26 cards)
Democriticus believed….
matter could not be broken down into smaller pieces i.e indivisible // the Greek word for atom is Atomos which is where we get the word Atom//
Greek Philosophers proposed that…
All matter consists of small particles //Particulate nature of Matter//
Gases/liquids can be spread by
diffusion
Dalton [1808] proposed an Atomic Theory (in a book he wrote) to explain results of experiments.
This Atomic Theory consisted of three main theories;
- All matter is made up of very small particles called atoms
- Atoms cannot be broken down into smaller particles
- Atoms cannot be created or destroyed
//His theory began to be questioned as a result of experiments carried out to test said theory towards the end of the nineteenth century//
Give a summary of Crookes [1875] research and methods.
He carried out research passing an electric current through a gas tube containing a gas at low pressure. He demonstrated radiation coming from the end of the tube connected to the negative end of the battery (cathode). The rays are invisible BUT when they strike the glass they cause it to glow or flouresce. He called this radiation Cathode rays as it comes from the negative end of the battery.
Lable a diagram of the apparatus //hint! maltese cross//
google it :/
What did Stoney [1891] Galway do?
Stoney proposed that the smallest electric charge be called an electron. // When their existence was proven by Thompson they were named as such//
J.J. Thomson calculated the ratio of the _________. He did this by…
J.J. Thomson is accredited with calculating the ratio of the charge of an electron to its mass //Cathode rays are negatively charged particles (electrons). J.J. Thomson is accredited with the discovery of the electron.(which Stoney had previously named)// He discovered the ratio of an electrons charge when he passed a narrow beam of cathode rays between metal plates. If there is no charge on the plates a spot is visible on the center of the screen. BUT if a charge is placed on the plates the beam is seen to move towards the plate with the positive charge. He then placed a large electromagnet outside the glass tube and found electrons are deflected in a magnetic field. He was able to calculate the ratio of the charge of the electron to its mass (e/m ratio) //Placed a magnet of x strength outside the glass tube.... ratio
Milikan’s ___ _____ ________ led him to discover the _______ __ ___ _______.
his oil drop experiment led him to discover the charge on an electron. (1.6 x 10 ^-19 Columbs) and it’s mass.
Describe Milikan’s oil drop experiment.
He sprayed tiny droplets of oil (negatively charged: x-rays were used to ionise the air and oil droplets pick up electrons to become negatively charged) between two charged metal plates. By focusing on one droplet and adjusting the charge on the plates he was able to observe that the droplet was attracted towards the positive plate and by varying the charge was able to suspend the droplet. From this he was able to calculate the mass and charge of the electron. //1.6 x 10^-19 Columbs - he subbed this into Thomson's e/m and found the mass of an electron to be 9.1 x 10^-31kg
J.J. Thompson proposed a model fro the structure of the atom: the ____ _______ model
The plum pudding model
What is the plum pudding model?
The plum pudding model is a model of the atom, proposed by J.J. Thomson. The proposed the atom is a sphere with positive and negative charged embedded in it at random. // The plum pudding model couldn't be explained and there were no experiments to back it up but it did explain why an electron would be neutral.//
Rutherford [1909] -
- The discovery of ___ _____.
- The discovery of ____ ______.
the nucleus
the proton
Rutherford’s Experiment with thin sheets of gold foil - summarise.
Studying the scattering of alpha particles (+) by thin sheets of gold foil. Most alpha particles went straight through but some were deflected at large angles and a few were actually reflected. This implies that the positive charge and the mass of the atoms of the gold foil were concentrated in a small dense core - this was called the nucleus. By continuing bombarding various substances with alpha particles Rutherford found that the particles were breaking up the nuclei of lighter atoms to release positively charged particles - protons. He also proposed that there must be another particle in the nucleus to keep positively charged particles from repelling each other. // He also proposed that there must be some sort of "electron cloud" surrounding the nucleus.//
Chadwick [1932] discovered the _____
Neutron
The Neutron was discovered by Chadwick by …
bombarding a sample of Beryllium with alpha particles he discovered a type of radiation with no charge being emitted. They had the same mass as protons and as they were neutral he called them neutrons.
Neutrons were used to bring about splitting of uranium to release nuclear energy in the atomic bomb and nuclear reactors.
In ancient Greece, Leucippus and his pupil _________ said that matter is made up of atoms.
Demicriticus
About two centuries ago ______ described atoms as tiny indivisible particles. Almost a century later _____ discovered the electron. A few years after that _______ carried out the experiment involving the scattering of alpha particles by gold foil, that resulted in the discovery of the nucleus
Dalton
Thomson
Rutherford
____ developed a theory restricting electrons in atoms to energy levels.
Bohr
In the early 1800’s _______ discovered that the atoms of each element have a characteristic positive charge. (the atomic number)
Moseley
Who stated that matter consists of tiny indivisible particles.
Dalton
Who discovered the nucleus of the atom?
Rutherford
What are cathode rays?
Beams of electrons
What was the purpose of Milikan’s oil drop experiments?
measure the charge on an elecrtron
