History of the atom.2 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 number
Who conducted the first experiments on cathode rays
William crookes
What is william crookes contributation?
Descovered cathode rays
descovered cathode rays musts consist of very small particles
describe the expeirment by crookes that discovered cathode rays and the obervations that occoured
passed electric current through a vacuume tube
(one with the maltease cross)
Observations: florsence in glass tube opposite to cathode
shadow coming from cross
what did crookes conclude when he conducted the expeirment on discovering cathode rays
radiation coming from the cathode
describe his second/ futher expeirment on cathose rays and describe his obervations
placed electric current through pressure vacum tube with light paddle wheel in center.
Observations: paddle wheel moves away from cathode.
cathode rays consist of very small particles
What did crookes conclude from his second expeirment on cathode rays
cathode rays consist of very small particles
who was the irish scientist that proposed the name electron
stoney
Who disovered the electron
JJ.thompson
name jj thomson’s contrubutions
discovered the electron
decrovered that electrons were negativily charged,discovered the charge to mass ratio of an electrom
Decribe JJ.thomsons expeirment on cathode rays and his obervations
passed cathode rays through tube in anode and low pressure vaccum tube.
placed two charged plated on either side (electric field).
when the plated where charged, the fluorsence caused by the glass being stuck appeared closer to the postive plate
Name the model of the atom that Thompson proposed
Plum pudding model
describe the model
a overall postive charge with electrons randomly embedded throughout . the atoms balances netural.
what are cathode rays
beams of negatively charged electrons
name properties of cathode rays
consists of negatice electrons
cause glass to floursence when struck
have enough energy to move a paddle wheel
are attracted to postive electric forces
name contrubutions did robert milikan
calculated an electron’s charge , exact charge to mass (oil drop expeirment)
who disovered the nucleus
ernest rutherford
name ernest rutherfords contributions
descovered the nucleus ( disproved plum pudding midel)
discovered postive protons in nucleus
what are alpha particles
consist of 2 protons and 2 neturnal emitted by radioactive isotopes trying to become stable
identical to helum nucleus
+2 charge
desctibe the goil foil expeirment
Bombared a thin gold foil with alpha particles. alpha particles from a radioactibve souce with a lead box
Describe the expected results of the goil foil expeirment
most of the alpha particles would go straight through undefelected or slight reflections
Describe the actual results of the goil foil expiernent
some alpha particles were deflected at large angles
a tiny number of alpha perticles refelected completely back along its orginal path, this could not be explained using the plum pudding model
what did rutherford, after his expeirment, conclude about the atom
-atoms were mostly empty space- most alpha particles passed through.
-the area in the center of an atom must be very small- postively charged and dense (some rebounded along its orginal paths)
-electrons must reside in an electron cloud surrounding the nucleus
describe the atomic / nuclear model of the stom
electrons in an electron cloud- the nucleus is small, postive dense. the atom is mostly empty space
what was james chadwick’s controbution
descovered the netron in the nucleus that has no charge. last subatomic partile to be discovered.
