the three subatomic particles
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Electron
Neutron
Proton
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In 1838, Michael Faraday passed current through the glass tube filled with rarefied air. Conducting the experiment he noticed a strange light arc with its beginning at the anode (the positive electrode) and its end almost at the cathode (the negative electrode). The only place where there was no luminescence was just in front of the cathode. The place is called "cathode dark space", "Faraday dark space", or "Crookes dark space". That was the beginning of the long and "turbulent" time of researches on that luminescence. And the luminescence is called "cathode rays".
MICHAEL FARADAY
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In this experiment, Faraday showed that the mass of elements was proportional to the quantity of electricity that passed through them.
2. George J. Stoney- he was a scientist who first suggested the term “ Electron” to refer to a negatively charged particle.
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3. Joseph John Thomson-was credited for his discovery of the first subatomic particle through his work with the discharge tube.
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4. Robert A. Millikan- independently measured the electrons charge through his OIL-DROP Experiment. He successfully attempted to detect and measure the effect of an individual subatomic particle.
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Using an atomizer, Millikan sprayed tiny droplets of oil which passed between two charged plates. Given a negative charge(-) by the electrons released from gas particles by x-rays, the oil particles were attracted toward the positive plate. He observed the speed of the droplets as they moved toward the positive plates. The smallest possible charge on a droplet was taken as the charge of an individual atom.
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The quantity is considered to be the basic unit charge and is given a value of one minus (1-)
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When the electron was discovered , the scientists searched for the positively charged particles.
1.Eugene Goldstein-
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Goldstein observed rays passing through the hole of a cathode in the cathode tube. These rays are made up of positive particles. Their characteristics depend on the gas inside the cathode tube.The lightest particle was obtained when Hydrogen gas was used.
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1. Sir James Chadwick- discovered the neutron in 1932. He found out that the particle was electrically neutral an and its mass was
approximately the same as that of the
proton.
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Proton
Symbol
Position in atom
Relative charge
Relative mass
Actual mass ( g)
p+
Inside the nucleus
1+
1
1.673x10-24
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Neutron
Symbol
Position in atom
Relative charge
Relative mass
Actual mass
n
Inside the nucleus
0
1
1.675x10-24
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Electron
Symbol e
Position in atom
Relative charge
Relative mass
Actual mass
moving around the nucleus
-1
01840
1
9.109x10-28
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Atomic structure
e
ee
e
e - - - - - - - - electron
n (s)p (s) - - - - - - - - - - - - - - - nucleus
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Atomic content of an atom
no. of protons = 11
no. of electrons =11
no. of neutrons = 12
12n11p
e11
Na2311Symbol
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Atomic Content of C126
no. of protons = 6
no. of neutrons = 12 - 6 = 6
no. of electrons = 6
(An atom is neutral in charge)
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Atomic Content of : N147
no. of protons = 7
no. of electrons = 7
no. of neutrons = 14 – 7
= 7
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Atomic Content of C146
no. of protons = 6
no. of neutrons = 14 – 6
= 8
no. of electrons = 6
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C146
C126
mass number
atomic number
Mass number = no. of p + no. of n
atomic number = no. of protons
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Isotopes
Name of element : carbon carbon
No. of protons : 6 6
No. of neutrons : 8 6
No. of electrons : 6 6
Isotopes are atoms of same elements which have the same atomic number but different mass number
C146 C12
6
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Isotopes
C146
C126
Burn in air Carbon dioxide Carbon dioxide
Mass 14 units 12 units
Radioactivity Give radiation Does not give radiation (stable)
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Extension : Isotopes ( For reference only )
8n6p
C146 nucleus
e01
7n7p
N147 nucleus
A neutron in a nucleus of breaks into
Electrons and energy are emitted to the surroundings
C14 .11 ep
Carbon -14 dating
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Properties of isotopes
Same chemical properties
Different physical properties
e.g. mass
b.p. and m.p.
radioactivity
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Actual mass VS relative mass
Mass of 1 C126
atom kg2610993.1 Or 12
Which one is more convenience?
Standard reference : 1 is equivalent to
kg
C
27
126
10661.1
12
1 of mass
Relative mass
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Simplified rule : We regard
Relative mass of 1p = 1
Relative mass of 1n = 1
Relative mass of 1e = very small
= 0
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Relative mass of isotopes
Si2814 Si29
14 Si3014
Relative mass 28 29 30
% abundance 92% 4.7% 3.1%
Do the three isotopes have the same chemical properties?
Yes
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It is difficult and not necessary
to separate the isotopes in most
of the reactions. Average
relative mass of silicon is used to
denote the mass of a silicon
atom.
Relative atomic mass of isotopes
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Relative atomic mass of silicon ( P.5 e.g.1 )
Si2814 Si29
14 Si3014
Relative mass
% abundance
28 29 30
92% 4.7% 3.1%
( Relative ) Atomic Mass of silicon
= 28 x 92% + 29 x 4.7% + 30 x 3.1%
= 28.053
= 28.05
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Ex1. Relative atomic mass of Chlorine
Cl3517 Cl37
17
Relative mass
% abundance
35 37
75.5% 24.5%
Atomic mass of Chlorine = 35 x 75.5% + 37 x 24.5%
= 35.5