The Atom Flashcards
(28 cards)
Atom
Smallest particle of a chemical element that can exist
•sub-atomic particles are Protons+, Neutrons and Electrons-
Matter
Anything that has mass and takes up space
Who named the atom
Greek philosopher- Democritus
•from greek word atomos(indivisible)
Greek philosophers
First to propose that matter was composed of small particles
Who proposed the theory about atoms
John Dalton
•English Chemist
Dalton’s Atomic Theory
1)All matter is made up of small particles called atoms
2)Atoms are indivisible.They cannot be broken down into smaller particles
This remained a theory because it was later proven false by the existence of sub atomic particles
Who discovered Cathode rays
William Crookes
English chemist
What are Cathode rays
Are streams of negatively charged particles called electrons
Crooked investigation
What happens when electric current is passed through a glass tube containing air at low pressure
-Crookes used a vacuum tube(glass with low air pressure inside):long glass tube with an electrode at each end
-Rays travelled from cathode to anode.
And they were named cathode rays
-to show the presence of radiation he put a Maltese cross inside the tube
It cast a sharp shadow at the end of the vacuum tube.
CNAP
Cathode Negative,Anode Positive
Crookes Paddle wheel experiment
-Consisted of a paddle wheel mounted on rails in front of the Cathode
-when the current was on,the paddle wheel rotated and travelled down the tube
-vanes always turned away from the cathode
Concluded:they were struck by particles from the cathode(electrons)
Cathode properties
1.Travel in straight lines
2.Cause glass to fluorescence (glow) when they strike it
3.posses enough energy to move a paddle wheel
4.deflected by electric and magnetic fields
Measured the charge on the electron
Robert Millikan
-American physicist
Oil drop experiment
an experiment to determine the size of charge on the electron
-sprayed tiny droplets of oil btwn two charged metal plates.
-used X-rays to ionise air,molecules lost electrons and became + Charged
-oil drops picked up the lost electrons and became negatively charged
He adjusted plates and suspended an oil droplet and measured its charge.
• Electron was identified as a negatively charged particle of very small mass
Thomson’s Plum pudding model of the atom
An atom is a sphere of positive charge with negative electrons embedded at random.
(When drawing the diagram draw a big positive sign then random - charges)
Discovery of the Nucleus
Ernest Rutherford
Ernest Rutherford
He studied the scattering of particles called alpha particles by passing them through a very thin sheet of gold foil.
Alpha particles
Are positively charged particles produced by certain radioactive substances and have the same structure as a helium nucleus
i.e 2 protons + and 2 neutrons
Rutherford’s experiment
Rutherford bombarded a thin piece of gold foil with alpha particles
-he used a phosphorescent screen made of zinc sulfide to detect the alpha particles
-Rutherford concluded that the positive charge and the mass of the atoms of the metal foil were concentrated in an small dense core called the nucleus of the atom
Observation and Conclusion of Rutherford’s experiment
1: Most of the alpha particles went through the gold foil
-Most of the atom is empty space
2:Some Alpha particles were deflected at large angles and some at small angles
-The particles came closer to the small positive dense core called the nucleus and some went close to the nucleus.
(Like charged repel each other )
3:Some Alpha particles were reflected along their original paths
-They had a head on collision with the nucleus.
Who discovered the Proton
Rutherford and his co-workers
How did Rutherford and his co-workers discover the proton
-they continued to bombard different substances with alpha particles
-when bombarding these substances They discoveredlight atoms such as oxygen and nitrogen, small positive charged particles were given off as a result of the bombardment
-Did not occur with heavier metals because the large positive nuclear charge repelled the alpha particles before they had a chance to break up the nucleus
-Alpha particles were breaking up the nuclei of the lighter atoms to release the positively charged particles.
New structure of the atom proposed by Rutherford
(When drawing) small nucleus and an electron cloud
i.e a small circle and one big circle
Summary of Rutherford’s work
1:Atom consists of a small dense positive core called the nucleus
2: Positive particles called protons were located in the nucleus
