Electron

Neutron

Proton

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

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.

3. Joseph John Thomson-was credited for his discovery of the first subatomic particle through his work with the discharge tube.

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.

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.

The quantity is considered to be the basic unit charge and is given a value of one minus (1-)

When the electron was discovered , the scientists searched for the positively charged particles.

1.Eugene Goldstein-

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.

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.

Proton

Symbol

Position in atom

Relative charge

Relative mass

Actual mass ( g)

p+

Inside the nucleus

1+

1

1.673x10-24

Neutron

Symbol

Position in atom

Relative charge

Relative mass

Actual mass

n

Inside the nucleus

0

1

1.675x10-24

Electron

Symbol e

Position in atom

Relative charge

Relative mass

Actual mass

moving around the nucleus

-1

01840

1

9.109x10-28

Atomic structure

e

ee

e

e - - - - - - - - electron

n (s)p (s) - - - - - - - - - - - - - - - nucleus

Atomic content of an atom

no. of protons = 11

no. of electrons =11

no. of neutrons = 12

12n11p

e11

Na2311Symbol

Atomic Content of C126

no. of protons = 6

no. of neutrons = 12 - 6 = 6

no. of electrons = 6

(An atom is neutral in charge)

Atomic Content of : N147

no. of protons = 7

no. of electrons = 7

no. of neutrons = 14 – 7

= 7

Atomic Content of C146

no. of protons = 6

no. of neutrons = 14 – 6

= 8

no. of electrons = 6

C146

C126

mass number

atomic number

Mass number = no. of p + no. of n

atomic number = no. of protons

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

Isotopes

C146

C126

Burn in air Carbon dioxide Carbon dioxide

Mass 14 units 12 units

Radioactivity Give radiation Does not give radiation (stable)

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

Properties of isotopes

Same chemical properties

Different physical properties

e.g. mass

b.p. and m.p.

radioactivity

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

Simplified rule : We regard

Relative mass of 1p = 1

Relative mass of 1n = 1

Relative mass of 1e = very small

= 0

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

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

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

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