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, Daltons 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

Nucleus

Proton

Neutron

Particle Symbol Mass

(kg)

Relative

Mass

Charge

(C)

Relative Charge

Proton p or 11H 1.67 x 10-27

1 a.m.u +1.6 x 10-19

+1

Neutron n or 10n 1.67 x 10-27

1 a.m.u 0 0

Electron e or 0-1e 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

+

electron proton

<

electron

pro

ton