MC test: Metallic bonding

Multiple choice test on 4.5 Metallic bonding

Use the following 'quiz' to test your knowledge and understanding of this sub-topic. You will need access to a periodic table (Section 6 of the IB data booklet).

If you get an answer wrong, read through the explanation carefully to learn from your mistakes.

What is meant by malleable?

 

Malleable is a typical property of metals e.g. gold, iron, aluminium, copper, silver, and lead. the opposite of malleable is brittle.

 


Why are metals good conductors of heat?

Like the explanation for electrical conductivity, it is all to do with the movement of the delocalized electrons transferring the energy as they move through the metal.

 

Why is the melting point of caesium lower than the melting point of lithium?

Lithium melts at 181 oC whereas caesium melts at 28.5 oC. This is due to the smaller size of the cations formed by lithium when the electrons are delocalised enabling them to pack more closely. 

 

Which metal is a liquid at room temperature (25 oC) and pressure (100 kPa)?

Only mercury and bromine are liquids under these conditions but bromine is not a metal.

 

What is meant by ductile?

Ductile technically means the ability to deform under tensile stress but in chemistry this is more often characterized by the material's ability to be stretched into a wire.

 

Other than iron, what other element is always present in steel?

Steel is an alloy of iron and carbon. The carbon content varies between about 0.002% and 2.1% by weight (although it is higher still in pig iron). Many other metals can also be added to give the steel particular properties, e.g. Mn, Ni, and Cr.

 

Which factors help to explain why alloys tend to be less malleable than pure metals ?

I. The added elements prevent the electrons on the pure metal from becoming delocalized.

II. The added elements may have a different charge and different radius to the principal metal which distorts the structure of the pure metal.

III. The distorted structure compared to the pure metal makes it harder for the close-packed layers of cations to slide over each other.

Alloys are still good conductors of heat and electricity which provides evidence that the electrons are still delocalized

 

Which is a correct statement about alloys?

Impurities always lower the melting point of a pure substance as the impurities distort the crystal structure making it easy to break down.

 

Which factors explain why magnesium has a higher melting point than sodium?

I. Mg2+ has a smaller ionic radius than Na+

II. Magnesium forms a divalent cation whereas sodium only forms a monovalent cation.

III. Delocalized electrons are more strongly attracted to the Mg2+ ion due to its higher charge density than the Na+ ion so that the Mg2+ cations pack more closely.

The higher charge density of the Mg2+ cations compared to Na+ cations is the main reason but this is due both to the decreased size of the Mg2+ ions and the fact that they have twice the charge.

 

Which is an alloy?

Bronze is an alloy of copper and tin, the remaining three are all elements.

 

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