SPM Chemistry (KBSM) Paper 1

02 Structure of Atom
2.1 Matter
2 Lessons
2.1.1 The Particle Theory of Matter
2.1.2 Changes in the State of Matter
2.2 The Atomic Structure
2 Lessons
2.2.1 History of Development
2.2.2 The Modern Atomic Model
2.3 Isotopes
1 Lesson
2.3.1 Isotopes
2.4 Arrangement of Electrons
1 Lesson
2.4.1 Electron Arrangement
2.5 Practices - Structure of Atom
03 Formular and Equations
03 Practices - Formulae and Equations
3 Exercises
3a Formulae and Equations I
3b Formulae and Equations II
3c Formulae and Equations III
04 Periodic Table
04 Practices - Periodic Table
3 Exercises
4a Periodic Table I
4b Periodic Table II
4c Periodic Table III
05 Chemical Bond
05 Practices - Chemical Bond
3 Exercises
5a Chemical Bond I
5b Chemical Bond II
5c Chemical Bond III
06 Electrochemistry
06 Practices - Electrochemistry
3 Exercises
6a Electrochemistry I
6b Electrochemistry II
6c Electrochemistry III
07 Acids and Bases
07 Practices - Acids and Bases
4 Exercises
7a Acids and Bases I
7b Acids and Bases II
7c Acids and Bases III
7d Acids and Bases IV
08 Salts
08 Practices - Salts
3 Exercises
8a Salts I
8b Salts II
8c Salts III
09 Manufactured Substances in Industry
09 Practices - Manufactured Substances in Industry
3 Exercises
9a Manufactured Substances in Industry I
9b Manufactured Substances in Industry II
9c Manufactured Substances in Industry III
10 Rate of Reaction
10 Practices - Rate of Reaction
3 Exercises
10a Rate of Reaction I
10b Rate of Reaction II
10c Rate of Reaction III
11 Carbon Compounds
11 Practices - Carbon Compounds
4 Exercises
11a Carbon Compounds I
11b Carbon Compounds II
11c Carbon Compounds III
11d Carbon Compounds IV
12 Oxidation and Reduction
12 Practices - Oxidation and Reduction
4 Exercises
12a Oxidation and Reduction I
12b Oxidation and Reduction II
12c Oxidation and Reduction III
12d Oxidation and Reduction IV
13 Thermochemistry
13 Practices - Thermochemistry
2 Exercises
13a Thermochemistry I
13b Thermochemistry II
14 Chemicals for Consumers
14 Practices - Chemicals for Consumers
2 Exercises
14a Chemical for Consumers I
14a Chemical for Consumers II
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2.4.1 Electron Arrangement

SPM Chemistry (KBSM) Paper 1 2.4 Arrangement of Electrons 2.4.1 Electron Arrangement
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Electron Arrangement in Atom

  1. We have learnt that electrons occupy orbits with definite energy level of an atom, as suggested by Neils Bohr.
  2. These orbits with definite energy level are known as the shell.
  3. Every single shell is capable of holding up to certain amount of electrons.
  4. The first shell can hold up to two electrons. This is called a duplet.
  5. The second shell can hold up to eight electrons. This is called an octet.
  6. The third shell can hold up to eighteen electrons.
  7. However, with the third shell, when eight electrons are present, extra stability is gained. The additional electrons go into the fourth shell before the third shell is completely filled.
  8. The way in which the electrons are distributed in the shells of an atom is called the electron arrangement of the atom
  9. The examples below show the electron arrangement of some elements:
Atom
Notes
Electrons Arrangement
  1. Lithium has 3 protons and 3 neutrons and three electrons as well.
  2. All the three electrons are arrange as follows:
  • Two electrons are filled in the first shell.
  • One electron is filled in the second shell.
  • The electron arrangement of carbon is 2.1
2.1 
  1. Chlorine has 17 protons and 18 neutrons and 17 electrons.
  2. All the three electrons are arrange as follows:
  • Two electrons are filled in the first shell.
  • Eight electrons are filled in the second shell.
  • Seven electrons are filled in the third shell.
  • The electron arrangement of chlorine is 2.8.7.
2.8.7
  1. Calcium has 20 protons and 20 neutrons and 20 electrons.
  2. All the three electrons are arrange as follows:
  • Two electrons are filled in the first shell.
  • Eight electrons are filled in the second shell.
  • Eight electrons are filled in the third shell.
  • Two electrons are filled in the forth shell.
  • The electron arrangement of carbon is 2.8.8.2.
2.8.8.2
Table below shows the arrangement of electrons of the first 20 elements in the periodic table. We shall learn periodic table in chapter 4.
Element Proton Number Number of Electron
Number of electron in
 Electron Arrangement
1st shell 2nd shell 3rd shell 4th shell
Hydrogen
1
1
1
0
0
0
 1
Helium
2
2
2
0
0
0
 2
Lithium
3
3
2
1
0
0
 2.1
Beryllium
4
4
2
2
0
0
 2.2
Boron
5
5
2
3
0
0
 2.3
Carbon
6
6
2
4
0
0
 2.4
Nitrogen
7
7
2
5
0
0
 2.5
Oxygen
8
8
2
6
0
0
 2.6
Fluorine
9
9
2
7
0
0
 2.7
Neon
10
10
2
8
0
0
 2.8
Sodium
11
11
2
8
1
0
 2.8.1
Magnesium
12
12
2
8
2
0
 2.8.2
Aluminium
13
13
2
8
3
0
 2.8.3
Silicon
14
14
2
8
4
0
 2.8.4
Phosphorus
15
15
2
8
5
0
 2.8.5
Sulphur
16
16
2
8
6
0
 2.8.6
Chlorine
17
17
2
8
7
0
 2.8.7
Argon
18
18
2
8
8
0
 2.8.8
Potassium
19
19
2
8
8
1
 2.8.8.1
Calcium
20
20
2
8
8
2
 2.8.8.2

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Electron arrangement in an atom

Valence Electron

Valence electrons are the electrons in the outermost shell.
  1. The electrons in the outermost shell of an atom are called valence electrons.
  2. The valence electrons have great significance in determining the chemical properties of an atom.
  3. Elements with the same number of valence electron have the same chemical properties.
 
Example:
Given that a sodium atom has 11 protons 12 neutrons. Find the number of valence electron in a sodium atom.Answer:
For an atom,
 
Number of electrons = number of protons = 11
 
Electron arrangement of sodium = 2.8.1
 
Therefore, sodium has 1 valence electron.
 
 
 
 
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