If you stop for a second and look around you, you will notice that most of the objects that you have are either made up of metals or contains a metal. For example, your watch has metal components, and your cooking pan too. If you have a piece of jewelry made up of pure silver or gold, you have a metallic solid in your hands!
- This article is about metallic solids.
- First, we will define metallic solids.
- Then, we will talk about the different properties of metallic solids.
- Last, we will define and explain what metallic alloys are and what makes them different from metallic solids.
What is a Metallic Solid?
Metallic solids are exactly what their name suggests: a solid made up of metal atoms only. Think of it like a "metals only" exclusive club. You can only be a member of this club if you are made entirely of metal atoms!
Metallic solids are compounds that are entirely comprised of metal atoms that are held together by metallic bonds.
Metallic bonding is a type of intramolecular force of attraction that occurs between a lattice of positive ions and a "sea" of delocalized electrons.
Feeling like you need a refresher on metallic bonds? Check out "Metallic bonding"!
Structure of Metallic Solids
When dealing with solids, there are two categories of solids that you must remember: crystalline and amorphous solids.
Crystalline solids are solids that have a well-arranged structure. Amorphous solids lack an organized structure.
Metallic solids are a type of crystalline solid, so their structure is arranged in a crystal lattice. In metallic solids, the crystal lattice consists of positive ions and free-flowing electrons that are also known as a "sea" of delocalized electrons.
What exactly does this mean? Let's look at a drawing that shows the lattice structure of a Sodium (Na) metal.
Notice that many free-flowing electrons surround the sodium atoms, and the attractive forces between the Na+ cations and the sea of delocalized electrons are what keep these identical metal atoms close together!
Metallic Solid Examples
Some common examples of metallic solids include aluminum (Al) metal and Potassium (Na) metal.
Aluminum (Al) is a metal found in group 13 (also called IIIA in some periodic tables). It has a high melting point of 660.32°C and has a face-centered cubic crystal lattice structure.
Potassium (K) is a group 1 metal and has a melting point of 63.38 °C. Potassium has a body-centered cubic crystal lattice structure.
Not sure what a face-centered or body-centered cubic lattice structure means? You might want to check out "Solids"!
Properties of Metallic Solids
Before diving into the properties of metallic solids, let's review the periodic trend of metals! Remember that, except for mercury (Hg), metals are solids at room temperature.
- Group I metals are known as the alkali metals (Li, Na, K, Rb, Cs, Fr).
- Group II metals are called the alkaline earth metals (Be, Mg, Ca, Sr, Ba, Ra).
- Groups 3-12 contain many transition metals such as Fe, Cu, Ag, and Au.
- Group 13-16 also have some metals called post-transition metals or poor metals (Al, Ga, In, Tl, Pb, Sn, Bi, and Po).
Periodic table of elements, Wikimedia Commons.
Metallic Character of Metallic Solids
We can describe elements as being good or poor metals depending on their metallic character, and the more an element exhibits the properties of metals, then the more metallic that element is. In the periodic table, metallic characters tend to increase from right to left, and down a group. Kind of like electronegativity, if you remember.
Maybe they are connected in some way? Hint: Yes!
The best way to remember the periodic trend of metallic characters is by looking at an example.
Which of the following metals will have the strongest metallic character? Cs, Ba, Fe or Na?
By looking at the periodic table, we now know that elements that are left and down the periodic table will exhibit a stronger metallic character. In this case, Cs will have the strongest metallic character, and the order of increasing metallic character would be: Fe < Ba < Na < Cs.
The general properties of metallic solids are high melting point, good conductivity, ductility, and malleability. Metallic solids are also lustrous (shiny). Let's break down each of these properties to better understand why are they so!
Melting Point of Metallic Solids
When you melt a crystalline solid, its crystal lattice gets broken down and the molecules change into a liquid state. The melting point is the temperature at which a solid turns into a liquid. When a solid reaches its melting point, the temperature then remains constant until the crystalline solid completely melts and becomes a liquid!
Although metallic solids usually have high melting points, some of them, such as the alkali metals (group 1), actually have low melting points. Metallic solids have melting points that are distinct to each metal.
Did you know that the metal Tungsten has one of the highest melting points known by chemists? The melting point of a body-centered cubic lattice of Tungsten is around 3400 °C. While another metal, namely mercury is already a liquid at -38 °C. Also, you can find basically anything in between among metallic solids, they have very diverse melting points.
Conductivity of Metallic Solids
Metallic solids are good conductors of electricity and heat because of their delocalized electrons which are able to freely move and transmit electrical charges.
Electrical conductivity is referred to as the ability to conduct electricity. Thermal conductivity is referred to as the ability to transfer heat.
The ability of metallic solids to conduct heat is the reason why most cooking utensils in your kitchen are made up of some type of metal because their delocalized electrons can acquire and transfer heat faster!
A very interesting experiment performed by scientists showed that if you add a droplet of a Sodium (Na) and Potassium (K) mixture to water (H2O), then water will turn into a metallic material with a golden color! This happens because it will borrow the outermost electron from both group 1 metals.
Ductility and Malleability of Metallic Solids
Why is copper (Cu) a great choice of metal to make electrical wiring? It is because of the ability of copper to conduct electricity and also copper is ductile and can be molded into the shape of a wire. Metallic solids are considered malleable and ductile.
A malleable metal is a metal that can be battered into thin sheets. A ductile metal is a metal that can be molded into different shapes (like a wire) without breaking.
For example, gold can be hammered into thin gold leaves that are widely used in decorations. And, if that is not interesting enough, you can now even buy gold leaf flakes to use next time you cook your favorite dish!
Luster
Why do metals shine? Again, it all comes down to the delocalized electrons that metallic solids have in their structure. Metals are lustrous (shiny) because the delocalized electrons can reflect off the light!
Metallic Alloys
When you combine different metals together, you create a metallic alloy that also has metallic bonding. Alloys can be interstitial or substitutional.
An alloy is referred to as a substance that is made up of a mixture of elements and has metallic properties.
Interstitial alloys are alloys that form between elements of different radii. These alloys have a more rigid lattice, are less ductile, and are also less malleable compared to metallic solids. A common example of an interstitial alloy is steel, which is made up of carbon and iron metals.
Substitutional alloys are alloys that form between metals of very similar radii. Because of the similar sizes, some of the metal atoms initially present get replaced by another metal atom. A common example of a substitutional alloy is brass, which is made up of copper and zinc atoms. In brass, the copper atoms get replaced by zinc atoms.
Metallic Solids - Key takeaways
- Metallic solids are compounds that are entirely composed of metal atoms that are held together by metallic bonds.
- Metallic bonds happen between a lattice of positive ions and a "sea" of delocalized electrons
- Metallic solids are lustrous, good conductors of electricity and heat, are malleable, ductile, and usually possess high melting points.
References
- AP Chemistry course and exam description, effective fall 2020. (n.d.). Retrieved April 8, 2022, from https://apcentral.collegeboard.org/pdf/ap-chemistry-course-and-exam-description.pdf?course=ap-chemistry
- Brown, T. L., LeMay, H. E., Bursten, B. E., Murphy, C. J., Woodward, P. M., Stoltzfus, M., & Lufaso, M. W. (2018). Chemistry: The central science (13th ed.). Harlow, United Kingdom: Pearson.
- Swanson, J. W. (2020). Everything you need to Ace Chemistry in one big fat notebook. Workman Pub.
- Malone, L. J., Dolter, T. O., & Gentemann, S. (2013). Basic concepts of Chemistry (8th ed.). Hoboken, NJ: John Wiley & Sons.
- https://media.nature.com/original/magazine-assets/d41586-021-02065-w/d41586-021-02065-w.pdf
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