1g. Can we deduce the type of bonding and structure from physical data?

Is it an ionic compound, covalent element/compound, giant structure - covalent or metallic?

(A question with answers - best done after working through Parts 2 to 5)

Doc Brown's Chemistry: Chemical Bonding and structure GCSE/IGCSE/O/IB/AS/A US grade 9-12 Level Revision Notes


Can we deduce the likely chemical bonding in a material from its physical and chemical properties?

The answer quite simply is YES (in most cases!), as long as you have studied parts 2 to 5 before attempting this question!

The table below describes the properties of ? compounds. The data is not specific to a substance, just 'typical properties'

Can you work out the bonding and structure of the substances A to F?

Solubility can be a bit subtle, so take care!

 Answers near the bottom of the page!

Substance Melting Point Boiling Point density (g/cm3) electrical conduction in solid electrical conduction when liquid solubility and electrical conduction in water Solubility in organic solvents like hexane
A 900oC 1720oC 1.5 none good soluble, good insoluble
B 1200oC 2000oC 7.5 good good insoluble insoluble
C 65oC 260oC 1.2 none none insoluble soluble
D 1100oC 2500oC 3.7 none none insoluble insoluble
E 120oC 65oC very small none none soluble, good soluble
F decomposes at high temperature decomposes at high temperature 1.2 moderate decomposes insoluble insoluble
               

What next?

Recommend next: Quizzes - after working trough Parts 2 to 5

Foundation tier (easier) Quiz on Structure, Properties & Chemical Bonding

Higher tier (harder) Quiz on Structure, Properties and Chemical Bonding

Word-fill quiz "Metal Structure and Ionic Compounds"

Word-fill quiz "The Structure and Uses of different forms of carbon"

Word-fill quiz "Simple Covalent Molecular Substances"

Word-fill quiz "Molecular modelling and bonding diagrams of covalent molecules"

 

Sub-index for: Part 1 Introduction to chemical bonding - why? how? and patterns

 

Index for ALL chemical bonding and structure notes

 

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Answers to the 'type of bonding' question

A is an ionic structure and bonding, giant ionic lattice, high melting/boiling point, only conducts when molten, the solubility and electrical conduction in water is extra evidence, but isn't definitive for substance A (see E).

Typical examples would be salts like sodium chloride, magnesium sulfate

B is a giant metallic lattice structure and metal bonds, high melting/boiling points, high density, conducts in solid, not just liquid.

Typical examples would be iron and copper.

C simple molecular structure, small molecules with covalent bonds, low melting/boiling point, no electrical conduction at all (no ions).

Typical examples would organic compounds like waxes which dissolve in organic solvents like hexane or propanone ('acetone').

D giant covalent lattice, very high melting/boiling, no electrical conduction, won't dissolve in anything.

Typical examples are carbon (diamond), silicon, silicon dioxide (silica) and many other minerals found in rocks.

I've made A to D quite straightforward (as long as Bonding Parts 2 to 5 have been studied), but I've

E simple molecular structure, small molecules with covalent bonds, low melting/boiling point, no electrical conduction when molten, however it does conduct when dissolved in water, so ions must be formed to conduct electricity. The latter is a 'red herring', if it had an ionic structure the melting/boiling points would be much higher and the liquid would have conducted.

Examples are the gases hydrogen fluoride, hydrogen chloride, hydrogen bromide and hydrogen.

These are all simple molecular substances, diatomic covalent molecules HF, HCl, HBr, HI), BUT they dissolve in water to form acids solutions containing the hydrogen ion (H+) and the corresponding halide ion (F, Cl, Br, I), hence the reason why the aqueous solution conducts electricity. Small covalent molecules often dissolve in organic solvents.

F Probably a thermally very stable giant covalent structure, but with weakly electrical conducting properties (even in the solid) due to delocalised electrons, completely insoluble. Its unlikely to be an ionic structure because it conducts in the solid. Metals do not decompose on heating to a high temperature and all metals will boil.

Examples might be carbon (graphite) and nanomaterials derived from carbon

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