CIE AS Chemistry (9701) exams from 2022

Revision Notes

2.1.8 Chemical Periodicity of Other Elements

Periodicity: Predicting Position & Properties

  • If the chemical and physical properties of an element are known, the position of that element in the Periodic Table can be predicted
  • Similarly, predictions can be made about the physical and chemical properties of elements if the position of the element in the Periodic Table is known

The Periodic Table - Flowchart, downloadable AS & A Level Chemistry revision notes

The diagram shows a flowchart of how to use the position and/or properties of an element to make predictions about its behaviour

Worked example: Deducing the position of an element in the Periodic Table

The Periodic Table - Worked example - Deducing the position of an element in the Periodic Table, downloadable AS & A Level Chemistry revision notes

Answer

Break the question down and systematically approach the question

  • Step 1: ‘Element X forms a chloride, which reacts with water to form a solution of pH 1’
    The low pH of the solution formed suggests that the chloride is a non-metallic chloride (group 13 to 17)
  • Step 2: ‘The oxide does not dissolve in or react with aqueous sodium hydroxide’
    Since aluminium oxide does reaction with sodium hydroxide, element G cannot be Group 13
  • Step 3: It forms an oxide which has a melting point of 1610 °C’
    This suggests a giant molecular (covalent) structure which corresponds to Group 14
  • Step 4: Element X cannot be carbon (which is in Group 14) as carbon dioxide is a gas whereas the element X oxide is a solid (with a melting point of 1610 °C)
  • Step 5: Element X is therefore a Group 14 element in Period 3 or lower
  • Note that this is an example of predicting the position of an element based on its physical and chemical properties

Worked example: Predicting physical and chemical properties of selenium

The Periodic Table - Worked example - Predicting physical and chemical properties of selenium, downloadable AS & A Level Chemistry revision notes

Answer

  • Step 1: Selenium is a nonmetal in Group 16 and if compared to sulfur, its structure is predicted to be a simple molecular structure
  • Step 2: Physical properties of simple molecular structures are low melting points, do not conduct electricity and are insoluble in water
  • Step 3: Chemical properties are:
    • Reaction with water: simple molecules do not react with water
    • Reaction with oxygen: reacts with oxygen to form an oxide of SeO2 (if compared with sulfur)
    • Reaction with chlorine: reacts with chlorine to form simple molecule of SeCl2 which can react with the water vapour in air to form hydrogen chloride (if compared with sulfur)
  • Note that this is an example of predicting the chemical and physical properties of an element based on its position in the Periodic Table

Worked example: Determining an unknown chloride compound

The Periodic Table - Worked example - Determining an unknown chloride compound, downloadable AS & A Level Chemistry revision notes

Answer

Answer 1:
Group 1 and 2 chlorides react with water to form colourless solutions of pH 6.5-7

Group 15 chlorides on the other hand react with water to form strong acidic solutions

Element X therefore belongs to Group 15 of the Periodic Table

Answer 2:
Group 15 chlorides gets hydrolysed in water, therefore this is a hydrolysis reaction

Answer 3:
The white fumes that are given off during this reaction is hydrogen chloride gas

Author: Francesca

Fran has taught A level Chemistry in the UK for over 10 years. As head of science, she used her passion for education to drive improvement for staff and students, supporting them to achieve their full potential. Fran has also co-written science textbooks and worked as an examiner for UK exam boards.
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