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Metallic Bonding

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Chemistry

You probably have sodium chloride, NaCl, in your house right now. You’ll know it as table salt. Although the crystals found in your salt shaker are generally small, you can grow larger crystals at home simply by heating up a saturated salt solution and allowing it to cool. These crystals will be hard and brittle. Pure sodium metal, on the other hand, is soft and malleable. You can easily cut it with a butter knife. What makes sodium so physically different when it is on its own?

What is metallic bonding?

Metals can form compounds with non-metals by donating their outer shell electrons (see Ionic Bonding for more information). The metals form positive ions whilst the non-metals, which accept the electrons, form negative ions. However, if a metal is on its own it cannot donate electrons because there is no non-metal atom that can accept them. Instead, it does something else: it bonds metallically.

A metallic bond is the electrostatic attraction between a lattice of positive ions and a sea of delocalised electrons.

Let’s break that down and explore each term together.

Delocalised electrons

When metal atoms bond with one another, their outer shell electron orbitals merge. The electrons are no longer confined to one particular atom and are free to move within the merged orbitals, which form a region that stretches throughout the whole metal. We say that these electrons are delocalised and that they form a sea of delocalisation.

Electrostatic attraction

The metal atoms form ions with a positive charge, since they are now no longer associated with their outer shell electrons.

Positively charged ions are known as cations.

The positive ions are then attracted to the negative sea of electrons by electrostatic attraction, much like the attraction in ionic compounds. The attraction spreads throughout the whole metal and so forms a giant lattice structure. 'Giant' simply means that it is made from a large but indeterminate number of atoms, and 'lattice' means that it contains a repeating arrangement.

Although the metal contains positive ions, overall no electrons have been lost. They are simply delocalised within the metal’s structure. Therefore, metals have a neutral charge and we represent them using just their chemical symbol. For example, the molecular formula of sodium is Na.

Metallic Bonding, metallic bonding diagram, StudySmarterA diagram showing the bonding in a metal.commons.wikimedia.org

Let’s go back to our example of sodium, Na. Sodium has the electron configuration . When sodium atoms bond with each other, their 3s orbitals merge and the valence electron within each atom’s orbital is free to move about in the newly merged region. This leaves positive ions with a charge of +1 surrounded by a sea of delocalised electrons, as shown below.

Metallic Bonding, sodium bonding, StudySmarterThe bonding in sodium, Na. Each sodium ion is attracted to the sea of delocalisation around it by electrostatic attraction. StudySmarter Originals

Beryllium, on the other hand, has the electron configuration and has two valence electrons. Each beryllium atom loses two electrons from its outer shell to form ions with a charge of +2.

Metallic Bonding, beryllium bonding, StudySmarterThe bonding in beryllium.StudySmarter Originals

Factors affecting the strength of metallic bonding

Some metals are much stronger than others. This is because of the difference in levels of electrostatic attraction within the different metals. There are two factors that affect the strength of the metal bond, and we’ll explore them now.

Charge on ion

A positive ion with a higher charge will be more attracted to the negative sea of electrons than one with a lower charge. Remember that a metal bond is simply the electrostatic attraction between positive metal ions and the sea of delocalised electrons, so this creates stronger bonding.

Aluminium, for example, loses three valence electrons to form an ion with a charge of +3. However, magnesium only loses two electrons to form an ion with a charge of +2, so has much weaker metallic bonds.

Size of ion

In metals with larger ions, the positive nucleus is a lot further away from the delocalised electrons. This weakens the electrostatic attraction between them. For example, the positive ions in magnesium and calcium both have the same charge, but calcium contains much larger ions and so has weaker metallic bonds.

Properties of metals

Because of their unique arrangement of positive ions within a sea of delocalised electrons, metals have certain properties that differentiate them from ionic and covalent compounds. We use copper, for example, to make wires and pipes. We wouldn’t use ionic compounds like sodium chloride for this. They would dissolve if dampened, and wouldn’t conduct electricity when solid. Furthermore, ionic compounds are brittle and break easily if stressed.

However, metals are quite different.

  • They have high melting and boiling points. This is because of the strength of their electrostatic attraction which stretches throughout the entire metal. Any of the factors explored above that increase the strength of the metallic bonding increase the melting and boiling points of a metal.
  • They are ductile, meaning they can be stretched out into wires, and malleable, meaning they can be hammered into shape. This is because the positive ions form regular rows within the sea of electrons which can roll over each other smoothly.
  • They are not brittle and generally strong. Again, this is because the rows of metal ions still maintain their bonds with the delocalised electrons when they slide over each other.
  • They are good conductors of heat and electricity, as the delocalised electrons are free to move throughout the metal and carry a charge. Metals that form ions with higher charges have more delocalised electrons and so are better conductors than metals with lower-charged ions.
  • They are insoluble.

Alloys

We know that sodium is relatively soft. Pure iron is too. This causes problems when making useful products out of metals. Iron nails wouldn’t be of much use if you could easily bend and distort them. To make pure metals stronger, we turn them into alloys.

Alloys are mixtures of two or more elements, at least one of which is a metal.

The different-sized atoms of the second element in an alloy disrupt the regular rows of metal ions, preventing them from sliding over each other as much, thus making them much harder. Iron often contains carefully controlled amounts of carbon, and steel is also a common alloy made from iron.

Metallic bonding, alloy structure, StudySmarterThe atoms in an alloy. Here, the smaller atoms disrupt the regular lattice structure of the larger metal atoms and prevent them sliding over each other. This strengthens the compound.StudySmarter Originals

Metallic Bonding - Key takeaways

  • A metallic bond is the electrostatic attraction between a lattice of positive metal ions and a sea of delocalised electrons.
  • Factors affecting the strength of metallic bonding include the charge of the ion and the size of the ion.
  • Metals are generally strong, not brittle, good conductors of heat and electricity, insoluble, and have high melting and boiling points.
  • Alloys are mixtures of two elements, at least one of which is a metal. They are stronger than pure metals.

Metallic Bonding

Metallic bonding is the electrostatic attraction between a lattice of positive metal ions and a sea of delocalised electrons.

Metals can conduct electricity because the sea of delocalised electrons found within the metal are free to move and carry a charge.

 Metals form bonds by merging their outer shell electron orbitals. The electrons within delocalise and are not attached to any particular metal atom. This forms positive metal ions within a sea of delocalised electrons. A metallic bond is simply the electrostatic attraction between the two.

Metallic bonds are strong because the strong electrostatic attraction between the positive metal ions and the negative sea of delocalised electrons extends throughout the entire metal.

Final Metallic Bonding Quiz

Question

 What is metallic bonding?

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Answer

The electrostatic attraction between a lattice of positive metal ions and a sea of delocalised electrons.


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Question

Outline the features of a metallic bond.

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Answer

  • Lattice of positive metal ions.
  • Sea of delocalised electrons.
  • Held together by electrostatic attraction between ions and electrons.

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Question

Magnesium atoms form metallic bonds. Which electrons do they lose to form stable ions?

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Answer

Both electrons from the 3s sub-shell.

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Question

Give the chemical formula for lithium.

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Answer

Li

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Question

Metals form a giant lattice structure. Explain the meaning of this term.


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Answer

'Giant' means it contains a large but indeterminate number of atoms. A 'lattice' is a regular, repeating arrangement of atoms, ions or molecules.

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Question

Do metals conduct electricity?


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Answer

Yes

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Question

Why are metallic bonds so strong?


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Answer

The strong electrostatic attraction between the positive metal ions and the negative sea of delocalised electrons extends throughout the entire metal.

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Question

Metals contain positive ions but are neutral overall. Explain why.


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Answer

Metals bond by merging their electron orbitals so their outer shell electrons are no longer associated with any one metal atom. This forms positive ions. However, the electrons remain within the structure and so no electrons are lost overall. This makes the metal neutral.

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Question

As the charge of the positive ion increases, the strength of the bonding within a metal ______.


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Answer

Increases

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Question

As the size of the positive ion increases, the strength of the metallic bonding ______.


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Answer

Decreases

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Question

Metals are good conductors of electricity. True or false?

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Answer

True

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Question

Compare the melting points of metals and simple covalent compounds. 


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Answer

  • Metals have much higher melting points than simple covalent compounds.
  • Simple covalent compounds are held together by weak intermolecular forces which don't require much energy to overcome.
  • Metals are held together by strong electrostatic attraction between the positive metal ions and the delocalised electrons.
  • This stretches in all directions through the substance and requires a lot of energy to overcome.


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Question

What word describes a metal’s ability to be hammered into shape?


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Answer

Malleable

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Question

One use of copper is in wires. Explain why the properties of copper make it suitable for this purpose.


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Answer

  • It is ductile, meaning it can be stretched out thinly into wires. 
  • It has a high melting point, so won’t melt if overheated. 
  • It is a good conductor of electricity, so it can carry a current.


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Question

Define ductile.

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Answer

Capable of being drawn out into wires or threads.

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Question

Define alloy.


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Answer

A mixture of two or more elements, at least one of which is a metal.


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Question

Brass is an alloy made primarily out of copper mixed with varying amounts of zinc. Explain why brass is stronger than pure copper. 


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Answer

Brass is stronger than pure copper because the different-sized zinc atoms disrupt the regular rows of copper atoms. This prevents them from sliding over each other easily.



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Question

Predict which of the following metals will have a higher melting point: sodium or potassium.


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Answer

Sodium

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Question

Predict which of the following metals will have a higher melting point: lithium or beryllium.

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Answer

Beryllium

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Question

Compare and contrast metallic and ionic structures.


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Answer

  • Both contain positive ions and electrostatic attraction. 
  • Both have high melting and boiling points. 
  • Both form giant lattice structures. 
  • Metals can conduct electricity when solid whereas ionic compounds can only conduct electricity when molten or aqueous.
  • Metals are insoluble, malleable and ductile whereas ionic compounds are soluble and brittle.

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