METALLIC BONDING
This page introduces the bonding in metals. It explains how the metallic bond arises and why its strength varies from metal to
metal.
The metals are the most numerous of the elements. About 80 of the 100 or so elements are metals. You know from your own
experience something about how metallic atoms bond together. You know that metals have substance and are not easily
torn apart. They are ductile and malleable. That means they can be drawn into shapes, like the wire for a paper clip, and their
shape can be changed. They conduct heat and electricity. They can be mixed to form alloys. How is it that metallic bonding
allows metals to do all these things?
The nature of metals and metallic atoms is that they have loosely held electrons that can be taken away fairly easily. Let's use
this idea to create a model of metallic bonding to help us explain these properties. Take potassium as an example. Its valence
electron can be represented by a dot. When packed in a cluster it would look like this:
The valence electron is only loosely held and can move to the next atom fairly easily. Each atom has a valence electron
nearby but who knows which one belongs to which atom. It doesn't matter as long as there is one nearby.
Packed in a cluster they look like this. These electrons are more or less free to move from one atom to another. Chemists
often describe metals as consisting of metal ions floating in a sea of electrons.
The mutual attraction between all these positive and negative charges bonds them all together - Atom to electron to atom to
electron and so forth. We have an array of atoms bonded to one another, that is, a network. The network of metallic bonding
holds that entire chunk of metal together. Each metallic bond gives strength and the network extends that strength over the
entire chunk of metal.
Therefore, a metallic bond is a bond that forms between metals that all “pool” their electrons to be shared.
If you are going to use this view, beware! Is a metal made up of atoms or ions? It is made of atoms.
Each positive centre in the diagram represents all the rest of the atom apart from the outer electron, but that electron hasn't
been lost - it may no longer have an attachment to a particular atom, but it's still there in the structure. Potassium metal is
therefore written as K not K+.
How can this particular model of metallic bonding be used to explain the properties of metals (such as electrical conductivity,
malleability, and thermal conductivity)? The key is in the loosely held electrons spread around and between all the metal
atoms, or metal ions.
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These electrons can move easily from one place to another, allowing for good electrical conductivity.
To a limited extent, the atoms can also move from one place to another and still remain in contact with and bonded to the
other atoms and electrons around them. Therefore, when you pound on gold, the atoms simply slide by each other,
remaining in contact.
Metallic bonding in transition elements
Transition metals tend to have particularly high melting points and boiling points. The reason is that they can involve more
electrons. The more electrons you can involve, the stronger the attractions tend to be.
The metallic bond in molten metals
In a molten metal, the metallic bond is still present, although the ordered structure has been broken down. The metallic bond
isn't fully broken until the metal boils. That means that boiling point is actually a better guide to the strength of the metallic
bond than melting point is. On melting, the bond is loosened, not broken.
Questions:
1) What are the electrons in an atom’s outer shell called?
2) What is a metallic bond?
3) Describe how a metallic bond forms between potassium atoms.
4) Why do transition metals have high melting and boiling points?
5) Why do metals conduct electricity well?