Monatomic

Monatomic

In physics and chemistry, monatomic is a combination of the words "mono" and "atomic," and means "single atom." It is usually applied to gases: a monatomic gas is one in which atoms are not bound to each other.

Under Standard Temperature and Pressure (STP), all of the noble gases are monatomic. These are helium, neon, argon, krypton, xenon and radon. The heavier noble gases can form compounds, but the lighter ones are unreactive. All elements will be monatomic in the gas phase at sufficiently large temperatures.

The only mode of motion of a monatomic gas is translation (electronic excitation is not important at room temperature). Thus in an adiabatic process, monatomic gases have an idealised gamma-factor (Cp/Cv) of 5/3 , as opposed to 7/5 for ideal diatomic gases where rotation (but not vibration at room temperature) also contributes, and:

:The heat capacity for monatomic gases at constant pressure (CP) is 2.5 R = 20.8 J.mol-1.K-1:The heat capacity for monatomic gases at constant volume (CV) is 1.5 R = 12.5 J.mol-1.K-1

where R is the gas constant.

Solids can also form monatomic powders when chemically separated from other materials. However, this is rare when removed through precipitation.


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  • Monatomic — Mon a*tom ic, adv. [Mon + atomic.] (Chem.) (a) Consisting of, or containing, one atom; as, the molecule of mercury is monatomic. (b) Having the equivalence or replacing power of an atom of hydrogen; univalent; as, the methyl radical is monatomic …   The Collaborative International Dictionary of English

  • monatomic — [män΄ə täm′ik] adj. [ MON + ATOMIC] 1. a) consisting of one atom: said of a molecule b) having one atom in the molecule 2. containing one replaceable atom or atomic group 3. MONOVALENT ( …   English World dictionary

  • monatomic — 1. Relating to or containing a single atom. 2. SYN: monovalent (1). * * * mon·atom·ic .män ə täm ik adj 1) consisting of one atom esp having but one atom in the molecule 2) MONOVALENT (1) * * * mon·atom·ic (mon″ə tomґik) [mon + atomic] …   Medical dictionary

  • Monatomic gas — In physics and chemistry, monatomic is a combination of the words mono and atomic, and means single atom. It is usually applied to gases: a monatomic gas is one in which atoms are not bound to each other. At standard temperature and pressure… …   Wikipedia

  • Monatomic ion — A monatomic ion is an ion consisting of one or more atoms of a single element (unlike a polyatomic ion, which consists of more than one element in one ion). For example calcium carbonate consists of the monatomic ion Ca2+ and the polyatomic ion… …   Wikipedia

  • monatomic gas — ▪ physical science       gas composed of particles (molecules) that consist of single atoms, such as helium or sodium vapour, and in this way different from diatomic, triatomic, or, in general, polyatomic gases. The thermodynamic behaviour of a… …   Universalium

  • monatomic gas — vienatomės dujos statusas T sritis fizika atitikmenys: angl. monatomic gas vok. einatomiges Gas, f rus. одноатомный газ, m pranc. gaz monoatomique, m …   Fizikos terminų žodynas

  • monatomic — adjective Date: 1848 consisting of one atom; especially having but one atom in the molecule …   New Collegiate Dictionary

  • monatomic — monatomically, adv. /mon euh tom ik/, adj. Chem. 1. having one atom in the molecule. 2. containing one replaceable atom or group. 3. having a valence of one. Also, monoatomic. [1840 50; MON + ATOMIC] * * * …   Universalium

  • monatomic — adjective Of an element, consisting of a single atom in the molecule; for example: the noble gases. Note: strictly speaking, a molecule has at least two atoms …   Wiktionary

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