SPM Chemistry (KSSM) Paper 1

01 Introduction to Chemistry
1.1 Chemistry and Its Importance
1 Lesson
1.1.1 Chemistry and Its Importance
1.2 Scientific Investigation
1 Lesson
1.2.1 Scientific Investigation
02 The Structure of Atoms
2.1 The Basic Concept of Matter
2 Lessons
2.1.1 The Particle Theory of Matter
2.1.2 The Three States of Matter
2.2 The History of Development of the Atomic Model
1 Lesson
2.2.1 The History of Development of the Atomic Model
2.3 The Structure of Atom
2 Lessons
2.3.1 The Structure of Atom
2.3.2 Electrons Arrangement in Atom
2.4 Isotopes and Their Uses
1 Lesson
2.4.1 Isotopes and Their Uses
2.5 The Structure of Atom - Practices
03 Concept of Mole, Formulae and Equations
3.1 Relative Atomic Mass and Relative Molecular Mass
1 Lesson
3.1.1 Relative Atomic Mass and Relative Molecular Mass
3.2 Concept of Mole
3 Lessons
3.2.1 Concept of Mole
3.2.2 Number of Mole and Mass
3.2.3 Number of Mole and Volume of Gases
3.3 Chemical Formulae
2 Lessons
3.3.1 Chemical Formulae
3.3.2 Formula of Ionic Compounds and Molecule
3.4 Chemical Equations
1 Lesson
3.4.1 Chemical Equations
3.5 Chemical Formulae and Equations - Practices (Coming Soon)
04 Periodic Table of Elements
4.1 The Development of Periodic Table
1 Lesson
4.1.1 Development of Periodic Table
4.2 Arrangement of Element in Periodic Table
1 Lesson
4.2.1 Arrangement of Electrons in Periodic Table
4.3 Group 18 Elements
1 Lesson
4.3.1 Group 18 Elements
4.4 Group 1 Elements
2 Lessons
4.4.1 Group 1 Elements
4.4.2 Chemical Properties of Group 1 Elements
4.5 Group 17 Elements
2 Lessons
4.5.1 Group 17 Elements
4.5.2 Chemical Properties of Group 17 Elements
4.6 Elements in Period 3
1 Lesson
4.6.1 Elements in Period 3
4.7 Transition Elements
1 Lesson
4.7.1 The Transition Elements
4.8 Periodic Table - Practices (Coming Soon)
1 of 3
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4.5.2 Chemical Properties of Group 17 Elements

SPM Chemistry (KSSM) Paper 1 4.5 Group 17 Elements 4.5.2 Chemical Properties of Group 17 Elements
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Chemical Properties of Halogens

  1. Group 17 elements are very reactive non-metals.
  2. The atoms all have 7 valence electrons, makes them have very similar chemical properties.
  3. During a chemical reaction, the atom gains one electron to form an ion with a charge of -1.
  4. The reactivity of group 1 decreases down the group.
  5. All group 17 elements are poisonous.
  6. Astatine is very radioactive.

Safety Precaution

  1. Fluorine, chlorine and bromine gases are poisonous.
  2. Therefore all the experiments involving these gases should be carried out in a fume chamber.
  3. The experiments involve fluorine are nor done in school.
  4. This is because fluorine is so reactive that it will react with most of the substance it comes into contact with.
  5. It is very difficult to conduct experiments involving fluorine.

Reaction of Halogens with Metals

 Chlorine + Iron

3Cl2 + 2Fe → 2FeCl3

Observation

The iron wool burns vigorously with a bright flame, forming a brown solid after the reaction.

Discussion

  1. Chlorine reacts with iron to form brown iron(III) chloride.
  2. The reaction of potassium with concentrated hydrochloric acid produces chlorine gas.
2KMnO4 + 16HCl → 2KCl + 2MnCl2 + 5Cl2 + 8H2O

Bromine + Iron

3Br2 + 2Fe → 2FeBr3

Observation

The iron wool glows brightly but less vigorously. A brown solid is formed.

Discussion

Bromine reacts with iron to form brown iron(III) bromide.

Iodine + Iron

3I2 + 2Fe → 2FeI3

Observation

The iron wool glows slowly with dim light. A brown solid is formed after the reaction.

Discussion

Iodine reacts with iron to form brown iron(III) iodide.

Note:

  1. Halogen is a reactive non-metal. It forms a salt when reacting with metals.
  2. The reactivity decreases down the group.
  3. Chlorine gas is poisonous. Excess chlorine gas is absorbed by the soda lime (sodium hydroxide) so that it does not escape to the surrounding.
  4. Iron wool rather than the iron piece is used to increase the rate of reaction.
 

Reaction of Halogens with Water

Halogens React with Water

Chlorine + Water

Cl2 + 2H2O → HCl + HOCl

Observation:

  1. Chlorine gas dissolves in water to form a pale yellow solution.
  2. The solution turns blue litmus paper red before it is bleached.

Discussion:

  1. The solution formed is acidic and contains a bleaching agent.
  2. Hypochlorous(I) acid is a strong bleaching agent. It decolourises the colour of litmus paper.

Bromine + Water

Br2 + 2H2O → HBr + HOBr

Observation:

  1. Bromine liquid dissolves slowly in water to form a yellowish-brown solution.
  2. The solution turns blue litmus paper red before it is bleached slowly.

Discussion:

Hypobromous(I) acid is a weak bleaching agent.

Iodine + Water

I2 + 2H2O → HI + HOI

Observation:

  1. Only a little iodine dissolves in water to form a yellowish solution.
  2. The solution turns blue litmus paper red but does not bleach it.

Discussion:

Hypoiodous(I) acid has very weak bleaching characteristic.

Notes:

  1. Chlorine, bromine and iodine are soluble in water to form an acidic solution.
  2. The solubility decreases down the group.
  3. Aqueous chlorine and bromine are bleaching agents.
  4. Aqueous iodine does not act as a bleaching agent.
  5. Chlorine gas is produced through the following reaction:

Reaction of Halogens with Sodium Hydroxide

Halogens React with Sodium Hydroxide

Chlorine + Sodium Hydroxide

Cl2 + 2NaOH → NaCl + NaOCl + H2O

Observation:

The greenish chlorine gas dissolves quickly in sodium hydroxide, forming a colourless solution.

Discussion:

Chlorine gas reacts with sodium hydroxide to form a salt of sodium chloride, sodium chlorate(I) and water.

Bromine + Sodium Hydroxide

Br2 + 2NaOH → NaBr + NaOBr + H2O

Observation:

The reddish-brown liquid bromine dissolves in sodium hydroxide, forming a colourless solution.

Discussion:

  1. Bromine liquid reacts with sodium hydroxide to form a salt of sodium bromide, sodium bromate(I) and water.
  2. The reaction is less reactive compared with chlorine.

Iodine + Sodium Hydroxide

I2 + 2NaOH → NaI + NaOI + H2O

Observation:

The black iodine crystals dissolve slowly in sodium hydroxide, forming a colourless solution.

Discussion:

  1. The reddish-brown liquid bromine dissolves in sodium hydroxide, forming a colourless solution.
  2. Solid iodine reacts slowly with sodium hydroxide to form a salt of sodium iodide, sodium iodate(I) and water.
  3. The reaction is least reactive among the three.

Safety Precaution

  1. Fluorine, chlorine and bromine gases are poisonous.
  2. Therefore all the experiments involving these gases should be carried out in a fume chamber.
  3. The experiments involve fluorine are nor done in school.
  4. This is because fluorine is so reactive that it will react with most of the substance it comes into contact with.
  5. It is very difficult to conduct experiments involving fluorine.

Explaining the Reactivity Trend of the Halogens

  1. The reactiveness of halogens decreases down the group.
  2. This can be explained as below:
    1. When a halogen atom reacts, it gains an electron to form a singly negative charged ion.
    2. As we go down the group from F => Cl => Br => I, the size of the atom increases due to an extra filled electron shell.
    3. The valence electrons are further and further from the nucleus, the attraction force between the electrons and the nucleus become weaker and weaker.
    4. Therefore the ability of the atom to attract electrons to fill the outermost shell reduces., which means the reactiveness of the atom reduces.
 
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