Chemical Periodicity of Other Elements (Cambridge (CIE) A Level Chemistry): Flashcards
Exam code: 9701
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An element forms a chloride that reacts with water to give a solution of pH 1. What does this suggest about the element's group?
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An element forms a chloride that reacts with water to give a solution of pH 1. What does this suggest about the element's group?
A low pH (strongly acidic) solution suggests the chloride is hydrolysed in water. This is characteristic of non-metallic (covalent) chlorides, placing the element in Groups 13–17 rather than Groups 1–2.
True or False?
Group 1 and Group 2 chlorides react with water to form strongly acidic solutions.
False.
Group 1 and Group 2 chlorides dissolve in water to form neutral or near-neutral solutions (pH 6.5–7.0). It is covalent chlorides (e.g. Group 15) that hydrolyse to produce strongly acidic solutions.
An element in Group 16 and Period 4 is predicted to have a .......... molecular structure and to form an oxide with the formula .......... .
An element in Group 16 and Period 4 is predicted to have a simple molecular structure and to form an oxide with the formula SeO2.
Define periodicity.
Periodicity is the repeating patterns of physical and chemical properties observed across the periods and groups of the periodic table, which allow predictions about unknown elements based on position.
An element forms an oxide with a very high melting point that does not react with NaOH. What group is the element likely in?
A very high melting point oxide with a giant covalent structure and no reaction with NaOH (unlike Al2O3) points to Group 14. Aluminium (Group 13) oxide reacts with NaOH, so Group 14 is the more likely assignment.
True or False?
White fumes produced when a covalent chloride reacts with water are hydrogen chloride gas.
True.
When covalent chlorides such as SiCl4 or PCl5 are hydrolysed by water, HCl (g) is produced. This appears as white fumes in the air.
When predicting properties from position, a simple molecular element in Group 16 is expected to have a .......... melting point and .......... electrical conductivity.
When predicting properties from position, a simple molecular element in Group 16 is expected to have a low melting point and no (zero) electrical conductivity.
How can the physical properties of an element be used to predict its position in the periodic table?
Properties such as melting point, electrical conductivity and the type of bonding in oxides or chlorides can indicate the group and period. For example, a high melting point giant covalent oxide places an element in Group 14, while ionic bonding in the oxide suggests a metal in Groups 1–2.
Selenium is in Group 16 and Period 4. Predict whether it reacts with water.
Selenium is predicted to form simple molecules (like sulfur). Simple molecular non-metals do not react with water. However, a selenium chloride (SeCl2) could react with water vapour in air to form HCl, analogous to sulfur's chloride.
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