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The Electronic Structure

of an AtomChapter 2 (4)

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An atom contains:Proton

Neutron and

Electron

Modern Atom Model

Electron

Nucleus } proton + neutron

Shell

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The Solar System

a) A planet movingaround the sun.

b) Solar systemcontains:

The sun

The planetsSunPlanet

Orbit

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Nucleus

Shell

Electron

Orbit

Sun

Planet

What Is The Similarities

and Differences?

Difference:

The orbit in solar system contain only 1 planet,

but the shell may contain more than 1 electron.

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Electron Arrangement

The electron arrangementis:

How the electrons of an atom arelocated around the nucleus.

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How Electrons Are

Arranged?

Number of electron = Number of

proton The first shell will be filled with

electrons till the maximum

numbersfollowed by the secondshell, third shell, etc.

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The standard representation for anatom

XA

Z

Symbol ofelements

Nucleonnumber

Protonnumber

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Example

Mg24

12

How manyelectrons does amagnesium atom

have?

12

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Example

Au197

79

How manyelectrons does amagnesium atom

have?

79

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Electronic Shells

Shell no 1

Shell no 2

Shell no 3

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Electron Arrangement

The first shell can be filledwith maximum of 2electrons.

The second shell can be filled

with maximum of 8electrons.

The third shell can be filledwith maximum of 18

electrons, but for elements1-20 the maximum electrons

can be filled is8 electrons.

The remains electron is filled

in the fourth shell.

An example: Argon

2.8.8

Ar40

18

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An example: Aluminum

2.8.3

Electron arrangement

Aluminum has 13 proton

number.

So, a neutral aluminum atom

has 13 electronsto be filled in

the shells.

Al27

13

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Fluorine has 9 protonnumber.

So, a neutral fluorine atom has

9 electronsto be filled in the

shells.

Fluorine2.7

F19

9

Electron Arrangement

Exercise:

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Neon2.8

Neon has 10 protonnumber.

So, a neutral neon atom has10 electronsto be filled in the

shells.

Ne20

10

Electron Arrangement

Exercise:

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Sodium has 11 protonnumber.

So, a neutral sodium atom has

11 electronsto be filled in the

shells.

Sodium

2.8.1

Na23

11

Electron Arrangement

Exercise

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Electron Arrangement

ExerciseCalcium has 20 protonnumber.So, a neutral calcium atom has

20 electronsto be filled in the

shells.

Calcium

2.8.8.2

Ca40

20

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Conclusion

The electron arrangement is

howthe electrons of an atom are

located around the nucleus.

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