Superatom

Key takeaways

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

Reference excerpt

In chemistry, a superatom is any cluster of atoms that seem to exhibit some of the properties of elemental atoms. One example of a superatom is the cluster Al13−. Sodium atoms, when cooled from vapor, naturally condense into clusters, preferentially containing a magic number of atoms (2, 8, 20, 40, 58, etc.), with the outermost electron of each atom entering an orbital encompassing all the atoms in the cluster. Superatoms tend to behave chemically in a way that will allow them to have a closed shell of electrons, in this new counting scheme.

Superhalogens Superhalogens are atom clusters with a higher electron affinity than chlorine, the atom with the highest electron affinity (3.62 eV). The concept was first formalized by Gennady L. Gutsev and Alexander I. Boldyrev in 1981. They were first clearly experimentally identified in 1999, precipitating a wave of subsequent research in the field.

Superalkalis Superalkalis are atom clusters with a lower ionization energy than caesium, the atom with the lowest ionization energy (3.89 eV). The concept was first formalized by Gutsev and Boldryev in 1982.

Aluminium clusters Certain aluminium clusters have superatom properties. These aluminium clusters are generated as anions (Al−n with n = 1, 2, 3, … ) in helium gas and reacted with a gas containing iodine. When analyzed by mass spectrometry one main reaction product turns out to be Al13I−. These clusters of 13 aluminium atoms with an extra electron added do not appear to react with oxygen when it is introduced in the same gas stream, indicating a halide-like character and a magic number of 40 free electrons. Such a cluster is known as a superhalogen. The cluster component in Al13I− ion is similar to an iodide ion or better still a bromide ion. The related Al13I−2 cluster is expected to behave chemically like the triiodide ion. Similarly it has been noted that Al14 clusters with 42 electrons (2 more than the magic numbers) appear to exhibit the properties of an alkaline earth metal which typically adopt +2 valence states. This is only known to occur when there are at least 3 iodine atoms attached to an Al−14 cluster, Al14I−3. The anionic cluster has a total of 43 itinerant electrons, but the three iodine atoms each remove one of the itinerant electrons to leave 40 electrons in the jellium shell. It is particularly easy and reliable to study atomic clusters of inert gas atoms by computer simulation because interaction between two atoms can be approximated very well by the Lennard-Jones potential. Other methods are readily available and it has been established that the magic numbers are 13, 19, 23, 26, 29, 32, 34, 43, 46, 49, 55, etc.

Al7 = the property is similar to germanium atoms. Al13 = the property is similar to halogen atoms, more specifically, chlorine. Al13I−x, where x = 1–13. Al14 = the property is similar to alkaline earth metals. Al14I−x, where x = 1–14. Al23 Al37 Al5O−4

Other clusters Li(HF)3Li = the (HF)3 interior causes 2 valence electrons from the Li to orbit the entire molecule as if it were an atom's nucleus. Li(NH3)4 = has one diffuse electron orbiting around Li(NH3)+4 core, i.e., mimics an alkali-metal atom. Be(NH3)4 = has two diffuse electrons orbiting around Be(NH3)2+4 core, i.e., mimics He-atom. VSi16F = has ionic bonding. A cluster of 13 platinum atoms becomes highly paramagnetic, much more so than platinum itself.

Superatom complexes Superatom complexes are a special group of superatoms that incorporate a metal core which is stabilized by organic ligands. In thiolate-protected gold cluster complexes, a simple electron counting rule can be used to determine the total number of electrons (ne) which correspond to a magic number:

n e = N ν A − M − z {\displaystyle n_{e}=N\nu _{A}-M-z}

where N is the number of metal atoms (A) in the core, v is the atomic valence, M is the number of electron withdrawing ligands, and z is the overall charge on the complex. For example the Au102(p-MBA)44 has 58 electrons and corresponds to a closed shell magic number.

Gold superatom complexes Au25(SMe)−18 Au102(p-MBA)44 Au144(SR)60

Other superatom complexes Ga23(N(Si(CH3)3)2)11 Al50(C5(CH3)5)12 Re6Se8Cl2 – In 2018 researchers produced 15-nm-thick flakes of this superatomic material. They anticipate that a monolayer will be a superatomic 2-D semiconductor and offer new 2-D materials with unusual, tunable properties. Organo− Zintl-based superatoms: [Ge9(CHO)3] and [Ge9(CHO)] [Cu43Al12](Cp*)12

Worked examples

Example 1 — a first encounter with Superatom

Start with the simplest possible case. Write down what Superatom claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, 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 Superatom 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 Superatom 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 Superatom

In research: Superatom appears in chemistry 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 Superatom 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: Superatom is common in secondary-school and first-year university syllabi. It links to neighbouring topics Atoms, Cluster chemistry, Quantum chemistry, so understanding it makes those chapters shorter.
In everyday life: Look for Superatom 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.

How to study Superatom in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Superatom 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 Superatom out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Superatom in simple terms?

In chemistry, a superatom is any cluster of atoms that seem to exhibit some of the properties of elemental atoms. One example of a superatom is the cluster Al13−.

Why does Superatom matter?

Because it connects several chemistry 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 Superatom?

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 Superatom.