Edexcel A Level Chemistry:复习笔记1.5.8 Predicting Structures

Predicting Structure & Bonding

 

  • Different types of structure and bonding have different effects on the physical properties of substances such as their melting and boiling points, electrical conductivity and solubility

Characteristics of Different Compound Structure Types Table

1.4.10-Characteristics-of-different-compound-structure-types-table

 

Predicting Physical Properties

Worked Example

Bonding & structure

The table below shows the physical properties of substances X, Y and Z4.1.2-Worked-Example-Bonding-and-Structure

Which one of the following statements about X and Y is completely true?

Statement 1: X has a giant ionic structure, Y has a giant molecular structure, Z is a metal

Statement 2: X is a metal, Y has a simple molecular structure, Z has a giant molecular structure

Statement 3: X is a metal, Y has a simple molecular structure, Z has a giant ionic structure

Statement 4: X has a giant ionic structure, Y has a simple molecular structure, Z is a metal

Answer

The correct answer is Statement 4

    • The relatively high melting point, solubility in water and electrical conductivity when molten suggest that X is a giant ionic structure.
    • The low melting point of Y suggests that little energy is needed to break the lattice which corresponds to a simple molecular structure. This is further supported by the low electrical conductivity and its being almost insoluble in water.
    • Compound Z has a very high melting point which is characteristic of either metallic or giant molecular lattices, however since it conducts electricity, compound Z must be a giant metallic lattice.

Worked Example

Bonding & structure

Compound X has the following properties:4.1.14-Worked-Example-2

What is the most probable structure of X?

A. Network covalent

B. Polar covalent molecule

C. Ionic lattice

D. Metallic lattice

Answer:

The correct option is A

    • A high melting point is characteristic of a giant structure, which could be metallic, ionic or covalent
    • The poor conductivity as a liquid and solid would match a giant covalent or network covalent structure

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