chemistry

Argon compounds

Argon compounds is a chemistry 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 Argon compounds rather than just read about it. In short: Argon compounds, the chemical compounds that contain the element argon, are rarely encountered due to the inertness of the argon atom. However, compounds of argon have been detected in inert gas matrix isolation, cold gases, and plasmas, and molecular ions containing argon have been made and also detected in space.

Key takeaways

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

Reference excerpt

Argon compounds, the chemical compounds that contain the element argon, are rarely encountered due to the inertness of the argon atom. However, compounds of argon have been detected in inert gas matrix isolation, cold gases, and plasmas, and molecular ions containing argon have been made and also detected in space. One solid interstitial compound of argon, Ar1C60 is stable at room temperature. Ar1C60 was discovered by the CSIRO. Argon ionises at 15.76 eV, which is higher than hydrogen, but lower than helium, neon or fluorine. Molecules containing argon can be van der Waals molecules held together very weakly by London dispersion forces. Ionic molecules can be bound by charge induced dipole interactions. With gold atoms there can be some covalent interaction. Several boron-argon bonds with significant covalent interactions have been also reported. Experimental methods used to study argon compounds have included inert gas matrices, infrared spectroscopy to study stretching and bending movements, microwave spectroscopy and far infrared to study rotation, and also visible and ultraviolet spectroscopy to study different electronic configurations including excimers. Mass spectroscopy is used to study ions. Computation methods have been used to theoretically compute molecule parameters, and predict new stable molecules. Computational ab initio methods used have included CCSD(T), MP2 (Møller–Plesset perturbation theory of the second order), CIS and CISD. For heavy atoms, effective core potentials are used to model the inner electrons, so that their contributions do not have to be individually computed. More powerful computers since the 1990s have made this kind of in silico study much more popular, being much less risky and simpler than an actual experiment. This article is mostly based on experimental or observational results. The argon fluoride laser is important in photolithography of silicon chips. These lasers make a strong ultraviolet emission at 193 nm.

Argonium

Argonium (ArH+) is an ion combining a proton and an argon atom. It is found in interstellar space in diffuse atomic hydrogen gas where the fraction of molecular hydrogen H2 is in the range of 0.0001 to 0.001. Argonium is formed when H2+ reacts with Ar atoms:

Ar + H+2 → ArH+ + H and it is also produced from Ar+ ions produced by cosmic rays and X-rays from neutral argon:

Ar+ + H2 → *ArH+ + H 1.49 eV. When ArH+ encounters an electron, dissociative recombination can occur, but it is extremely slow for lower energy electrons, allowing ArH+ to survive for a much longer time than many other similar protonated cations.

ArH+ + e− → ArH* → Ar + H Artificial ArH+ made from earthly Ar contains mostly the isotope 40Ar rather than the cosmically abundant 36Ar. Artificially it is made by an electric discharge through an argon-hydrogen mixture.

Natural occurrence In the Crab Nebula, ArH+ occurs in several spots revealed by emission lines. The strongest place is in the Southern Filament. This is also the place with the strongest concentration of Ar+ and Ar2+ ions. The column density of ArH+ in the Crab Nebula is between 1012 and 1013 atoms per square centimeter. Possibly the energy required to excite the ions so that then can emit, comes from collisions with electrons or hydrogen molecules. Towards the Milky Way centre the column density of ArH+ is around 2×1013 cm−2.

Cluster argon cations The diargon cation, Ar+2 has a binding energy of 1.29 eV. The triargon cation Ar+3 is linear, but has one Ar−Ar bond shorter than the other. Bond lengths are 2.47 and 2.73 ångströms. The dissociation energy to Ar and Ar2+ is 0.2 eV. In line with the molecule's asymmetry, the charge is calculated as +0.10, +0.58 and +0.32 on each argon atom, so that it greatly resembles Ar+2 bound to a neutral Ar atom. Larger charged argon clusters are also detectable in mass spectroscopy. The tetraargon cation is also linear. Ar+13 icosahedral clusters have an Ar+3 core, whereas Ar+19 is dioctahedral with an Ar+4 core. The linear Ar+4 core has +0.1 charge on the outer atoms, and +0.4 charge on each or the inner atoms. For larger charged argon clusters, the charge is not distributed on more than four atoms. Instead the neutral outer atoms are attracted by induced electric polarization. The charged argon clusters absorb radiation, from the near infrared, through visible to ultraviolet. The charge core, Ar+2, Ar+3 or Ar+4 is called a chromophore. Its spectrum is modified by the first shell of neutral atoms attached. Larger clusters have the same spectrum as the smaller ones. When photons are absorbed in the chromophore, it is initially electronically excited, but then energy is transferred to the whole cluster in the form of vibration. Excess energy is removed by outer atoms evaporating from the cluster one at a time. The process of destroying a cluster by light is called photofragmentation. Negatively-charged argon clusters are thermodynamically unstable, and therefore cannot exist. Argon has a negative electron affinity.

Argon monohydride Neutral argon hydride, also known as argon monohydride (ArH), was the first discovered noble gas hydride. J. W. C. Johns discovered an emission line of ArH at 767 nm and announced the find in 1970. The molecule was synthesized using X-ray irradiation of mixtures of argon with hydrogen-rich molecules such as H2, H2O, CH4 and CH3OH. The X-ray excited argon atoms are in the 4p state. Argon monohydride is unstable in its ground state, 4s, as a neutral inert gas atom and a hydrogen atom repel each other at normal intermolecular distances. When a higher-energy-level ArH* emits a photon and reaches the ground state, the atoms are too close to each other, and they repel and break up. However a van der Waals molecule can exist with a long bond. However, excited ArH* can form stable Rydberg molecules, also known as excimers. These Rydberg molecules can be considered as a protonated argon core, surrounded by an electron in one of many possible higher energy states.

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with Argon compounds

Start with the simplest possible case. Write down what Argon compounds 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 Argon compounds 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 Argon compounds 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 Argon compounds

In research: Argon compounds 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 Argon compounds 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: Argon compounds is common in secondary-school and first-year university syllabi. It links to neighbouring topics Argon, Argon compounds, Chemical compounds by element, so understanding it makes those chapters shorter.
In everyday life: Look for Argon compounds 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.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “Argon compounds” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Argon compounds in 20 minutes

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

Frequently asked questions

What is Argon compounds in simple terms?

Why does Argon compounds 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 Argon compounds?

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 Argon compounds.