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Atomic Structure

8/6/2019 Form 5 Matter and Atomic)

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John Dalton (1807)

• British Schoolteacher 

 –based his theory on

others’ experimental data

• Solid Sphere Model

 –atom is a

uniform,solid sphere

8/6/2019 Form 5 Matter and Atomic)

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John Dalton

Dalton’s Four Postulates

1. Elements are composed of smallindivisible particles called atoms.

2. Atoms of the same element are

identical. Atoms of differentelements are different.

8/6/2019 Form 5 Matter and Atomic)

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3. Compounds contain atoms of 

more than one element

4. In a compound, atoms of different

elements always combine the same

way.

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J. J. Thomson (1903)

• Cathode Ray TubeExperiments

 –beam of negative

particles

• Discovered Electrons

 –negative particles within

the atom

• Plum-pudding Model

8/6/2019 Form 5 Matter and Atomic)

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J. J. Thomson (1903)

Plum-pudding Model

 –positive sphere(pudding) with

negative electrons

(plums) dispersed

throughout

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Ernest Rutherford (1911)

• Gold Foil Experiment

• Discovered the nucleus –dense, positive

charge in the center of 

the atom• Nuclear Model

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Ernest Rutherford (1911)

• Nuclear Model

 –dense, positive nucleus surrounded by negative

electrons

8/6/2019 Form 5 Matter and Atomic)

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James Chadwick (1932)

Discovered the neutron

 – neutral particleswithin the atom

8/6/2019 Form 5 Matter and Atomic)

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Subatomic Particles

P O S I

C H A R

P R O T O

N E U T

C H A R

N E U T R O

N U C L E

N E G A T I V E

E L E C T R

A T O M

NUCLEUS ELECTRONS

PROTONS NEUTRONS NEGATIVE CHARGE

POSITIVECHARGE

NEUTRALCHARGE

ATOM

8/6/2019 Form 5 Matter and Atomic)

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Proton, electron and 

neutron

8/6/2019 Form 5 Matter and Atomic)

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Subatomic Particles

P O S IC H A R

P R O T O

N E U TC H A R

N E U T R O

N U C L E

N E G A T I V E

E L E C T R

A T O M

Most of the atom’s mass. Number 

equals the # of...

in a neutral atom

NUCLEUS ELECTRONS

PROTONS NEUTRONS NEGATIVE CHARGE

POSITIVECHARGE

NEUTRALCHARGE

ATOM

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 Atomic Structure

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8/6/2019 Form 5 Matter and Atomic)

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How do we compute for the number 

of protons, electrons and neutrons

in a neutral atom?

8/6/2019 Form 5 Matter and Atomic)

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• Proton Number 

= Number of Proton

• Nucleon Number 

= Number of proton +

number of neutron

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Example

Determine :

C126

Proton Number =

Nucleon Number =Number of 

proton = 6, electron = 6

neutron = Nucleon-proton

= 12-6

= 6

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Ions

• Charged particle

• Positive ion

proton more than electron

• Negative ion

proton less than electron

• Neutral (no charge)proton = electron

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Isotopes

• Atoms that have the same number of 

protons but different numbers of 

neutrons.

Ex. 11H – hydrogen

2

1

H – deuterium

31H – tritium

8/6/2019 Form 5 Matter and Atomic)

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PeriodGroup

Alkali

Metal

NobleGas

H

alogen

AlkaliEarth

Metal

2.4

Transition Metal