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🌀  Unit 3 - Intermolecular Forces and Properties

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⚖️  Unit 7 - Equilibrium

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🤺  AP Chemistry Essentials

2.4 Metallic Bonding and Alloys

#metallicsolids

#alloys

⏱️  3 min read

written by

anika p

Dalia Savy

dalia savy

Dylan Black

dylan black

(editor)

September 18, 2020


Metallic Bonding

Although ionic and covalent bonds are more common, metallic bonding describes a lattice of cations surrounded by a ‘sea’ of valence electrons🌊. The nucleus and core electrons of the metal stay in place, but the valence electrons are very mobile.

Electrons usually belong to a certain atom but in metals, they move so much that they don't belong to one, single atom.

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This ‘sea’ of valence electrons contributes to metal properties:

  1. Metals conduct electricity⚡ - because of delocalization of electrons in metals, electrons can move freely. This allows metals to conduct charge or, as we'll see in a future unit, be used in redox reactions.

  2. Metals are malleable and ductile - Metals, because they are less rigid, can be bent and spun into wire🔌.

Comparing Solids

When comparing properties among the different solids, remember this chart:

Type of SolidForm of Unit ParticlesForces Between ParticlesPropertiesExamples
Molecular🧊Atoms or MoleculesLDFs, dipole-dipole, hydrogen bondsfairly soft, low melting point, bad conductorArgon, methane, sucrose, dry ice
Covalent-Network💎Atoms connected in a network of covalent bondsCovalent bondsVery hard, very high melting point, bad conductordiamond, quartz
Ionic🧂Positive and negative ionsElectrostatic attractionsHard and brittle, high melting point, bad conductorsalts (NaCl)
Metallic✨AtomsMetallic bondsvarying hardness and melting points, good conductor, malleable, ductilemetals! Cu, Fe, Al

Table Courtesy of unknown source

Right now, you should only be very familiar with the two bolded rows. The others are covered in unit 3 in more depth!

Alloys

Metals can also bond with each other and become alloys. Alloys can be formed when two metals are in their liquid form being mixed together. When this mixture cools, the alloy is formed.

There are two types:

  • Interstitial alloys: Smaller atoms fill the interstitial spaces between larger atoms

    • An example of an interstitial alloy is steel🍳. Steel is made up of iron and carbon. Carbon is in the interstices of iron and the amount of carbon affects the properties of the sample of steel.

    • The ratio of carbon to iron significantly changes the properties of the steel.

  • Substitutional alloys: An atom of one element substitutes an atom of another element of similar size

    • Brass🎺 is an example of a substitutional alloy. Zinc is substituted for copper.

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    Image Courtesy of Chemistry LibreTexts

Alloys are harder and stronger than pure metals because the added elements distorts the structure and properties. Alloys are also less malleable than pure metals.

Check your Understanding

*This question is similar to one discussed on the Advanced Placement YT*

It goes over content reviewed this key topic and the previous key topic.

A student ran an experiment to see if the following solids conduct electricity.

SolidsDoes it conduct electricity?
Fe (s)yes
FeCl2 (s)no

(a) Explain the results the student saw.

Sample response (a)

  • This student found that a sample of iron conducted electricity since it is a metal. Metals have delocalized valence electrons, usually displayed by the sea of electrons diagram, allowing them to be good conductors of electricity.

  • The student found that the sample of FeCl2 didn't conduct electricity because it is an ionic solid. Ionic solids have a lattice structure. Therefore, electrons cannot move freely and the sample didn't conduct electricity.

(b) Is there anything that could have been different in this experiment to see the FeCl sample conduct electricity?

Recall: As long as there are mobile valence electrons, the sample will conduct electricity. There are two ways to do that. Either of the following responses are acceptable.

  1. Melt the FeCl2 solid and then test it for conductivity. The liquid FeCl2 would conduct electricity since the ions would be mobile and able to flow.

  2. Dissolve the FeCl2 solid into water. In an aqueous solution, the ions are able to flow and conduct electricity.

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