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PRE UNIVERSITYCHEMISTRY

SEMESTER 1

CHAPTER 1 : MATTER

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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 asubstance.

Later, physicist J.J. Thomson (1897) found out thatatom are made up of even smaller particles withnegative charge electron, Daltons theory was beingrejected.

After that, subatom with a positive charge protonwas discovered by Rutherford in the center of theatom.

At the same decade, Neils Bohr discover that

electrons surrounding nucleus similar as planetsurrounding the Sun, and electrons move about in arich 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.

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Electron

Nucleus

Proton

Neutron

Particle Symbol Mass

(kg)

Relative

Mass

Charge

(C)

RelativeCharge

Proton p or 11H 1.67 x10-27

1 a.m.u +1.6 x10-19

+1

Neutron n or 10n 1.67 x

10-27

1 a.m.u 0 0

Electron e or 0-1e 9.11 x10-31

_1_ amu1834

-1.6 x10-19

-1

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

electric field and magnetic field

+

electron proton

<

electr

on

proto

n