engineering

Periodic table (crystal structure)

Periodic table (crystal structure) is a engineering topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Periodic table (crystal structure) rather than just read about it. In short: This articles gives the crystalline structures of the elements of the periodic table which have been produced in bulk at STP and at their melting point (while still solid) and predictions of the crystalline structures of the rest of the elements. Standard temperature and pressure The following table gives the crystalline structure of the most thermodynamically stable form(s) for elements that are solid at standard t…

Key takeaways

Periodic table (crystal structure) belongs to engineering; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Periodic table (crystal structure) to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Periodic table (crystal structure) from memory before moving on to harder problems.

Reference excerpt

This articles gives the crystalline structures of the elements of the periodic table which have been produced in bulk at STP and at their melting point (while still solid) and predictions of the crystalline structures of the rest of the elements.

Standard temperature and pressure The following table gives the crystalline structure of the most thermodynamically stable form(s) for elements that are solid at standard temperature and pressure. Each element is shaded by a color representing its respective Bravais lattice, except that all orthorhombic lattices are grouped together.

Melting point and standard pressure The following table gives the most stable crystalline structure of each element at its melting point at atmospheric pressure (H, He, N, O, F, Ne, Cl, Ar, Kr, Xe, and Rn are gases at STP; Br and Hg are liquids at STP.) Note that helium does not have a melting point at atmospheric pressure, but it adopts a magnesium-type hexagonal close-packed structure under high pressure.

Predicted structures The following table give predictions for the crystalline structure of elements 85–87, 100–113 and 118; all but radon have not been produced in bulk. Most probably Cn and Fl would be liquids at STP (ignoring radioactive self-heating concerns). Calculations have difficulty replicating the experimentally known structures of the stable alkali metals, and the same problem affects Fr; nonetheless, it is probably isostructural to its lighter congeners. The latest predictions for Fl could not distinguish between FCC and HCP structures, which were predicted to be close in energy. No predictions are available for elements 115–117.

Structure types The following is a list of structure types which appear in the tables above. Regarding the number of atoms in the unit cell, structures in the rhombohedral lattice system have a rhombohedral primitive cell and have trigonal point symmetry but are also often also described in terms of an equivalent but nonprimitive hexagonal unit cell with three times the volume and three times the number of atoms.

Close packed metal structures

The observed crystal structures of many metals can be described as a nearly mathematical close-packing of equal spheres. A simple model for both of these is to assume that the metal atoms are spherical and are packed together as closely as possible. In closest packing, every atom has 12 equidistant nearest neighbours, and therefore a coordination number of 12. If the close packed structures are considered as being built of layers of spheres, then the difference between hexagonal close packing and face-centred cubic is how each layer is positioned relative to others. The following types can be viewed as a regular buildup of close-packed layers:

Mg type (hexagonal close packing) has alternate layers positioned directly above/below each other: A,B,A,B,... Cu type (face-centered cubic) has every third layer directly above/below each other: A,B,C,A,B,C,... α-La type (double hexagonal close packing) has layers directly above/below each other, A,B,A,C,A,B,A,C,.... of period length 4 like an alternative mixture of fcc and hcp packing. α-Sm type has a period of 9 layers A,B,A,B,C,B,C,A,C,... Precisely speaking, the structures of many of the elements in the groups above are slightly distorted from the ideal closest packing. While they retain the lattice symmetry as the ideal structure, they often have nonideal c/a ratios for their unit cell. Less precisely speaking, there are also other elements are nearly close-packed but have distortions which have at least one broken symmetry with respect to the close-packed structure:

In type is slightly distorted from a cubic close packed structure α-Pa type is distorted from a hexagonal close packed structure

Illustrations

Worked examples

Example 1 — a first encounter with Periodic table (crystal structure)

Start with the simplest possible case. Write down what Periodic table (crystal structure) claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Periodic table (crystal structure) before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Periodic table (crystal structure) ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Periodic table (crystal structure)

In research: Periodic table (crystal structure) appears in engineering research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Periodic table (crystal structure) in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Periodic table (crystal structure) is common in secondary-school and first-year university syllabi. It links to neighbouring topics Chemical elements by crystal structure, Periodic table, so understanding it makes those chapters shorter.
In everyday life: Look for Periodic table (crystal structure) outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Periodic table (crystal structure) in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Periodic table (crystal structure) means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Periodic table (crystal structure) out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Periodic table (crystal structure) in simple terms?

Why does Periodic table (crystal structure) matter?

Because it connects several engineering ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Periodic table (crystal structure)?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Periodic table (crystal structure).