Chemistry Form 6 Chap 01

PRE UNIVERSITY CHEMISTRY SEMESTER 1


CHAPTER 1 : MATTER

1.1

The Atom

1.1.1 Historical development of atomic theory
When atom was first discovered by John Dalton (1808), he claim that atom are the simplest unit in a substance.
Later, physicist J.J. Thomson (1897) found out that atom are made up of even smaller particles with negative charge – electron, Dalton’s theory was being rejected.
After that, subatom with a positive charge – proton was discovered by Rutherford in the center of the atom.
At the same decade, Neils Bohr discover that electrons surrounding nucleus similar as planet surrounding the Sun, and electrons move about in a rich electron region called orbital.
Few years later, Chadwick discovered that not only proton exist in the center of an atom but also a non-charge subatom – neutron.

Electron

Neutron

Nucleus Proton

Particle

Symbol

Mass (kg)

Relative Mass

Charge (C)

Relative Charge

Proton

p or

1 H 1

1.67 x 10-27

1 a.m.u

+1.6 x 10-19

+1

Neutron

n or

1 n 0

1.67 x 10-27

1 a.m.u

0

0

Electron

e or

0 e -1

9.11 x 10-31

_1_ amu 1834

-1.6 x 10-19

-1

The path of moving protons, electrons and neutrons is deflected by both electric field and magnetic field

neutron

β

α

electron

electron

North proton β

–

proton

α