Diatomic molecule

src: i.ytimg.com

Diatomic molecules are molecules consisting only of two atoms, of the same or different chemical elements. The prefix in - is of Greek origin, meaning "two". If a diatomic molecule consists of two atoms of the same element, such as hydrogen (H ₂ ) or oxygen (O ₂ ), it is said to be homonuclear. Otherwise, if the diatomic molecule consists of two different atoms, such as carbon monoxide (CO) or nitric oxide (NO), the molecule is said to be heteronuclear.

The only chemical elements that form a homonuclear diatomic molecule stable at standard temperature and pressure (STP) (or typical lab conditions 1 bar and 25 ° C) are hydrogen gas (H ₂ ), nitrogen (N ₂ ), oxygen (O ₂ ), fluorine (F ₂ ), and chlorine (Cl ₂ ).

The noble gases (helium, neon, argon, krypton, xenon, and radon) are also gases in STP, but they are monatomic. Dionomic gases of homonuclear and noble gases together are called "elemental gases" or "molecular gases", to distinguish them from other gases that are chemical compounds.

At slightly higher temperatures, halogen bromine (Br ₂ ) and iodine (I ₂ ) also form diatomic gases. All halogens have been observed as diatomic molecules, except astatine, which are uncertain.

The mnemonic BrINClHOF , pronounced "Brinklehof", and HONClBrIF , pronounced "Honkelbrif", and HOFBrINCl (pronouced as Hofbrinkle) have been created to help remember the list of diatomic elements.

Other elements form diatomic molecules when vaporized, but these diatomic species repolymerize when cooled. Heating ("crack") phosphorus element provides phosphorus, P ₂ . Sulfur vapor is mostly disulfur (S ₂ ). Dilithium (Li ₂ ) is known in the gas phase. Ditungsten (W ₂ ) and dimolybdenum (Mo ₂ ) are formed with sextuple bonds in the gas phase. The bond in the homonuclear diatomic molecule is non-polar. Dirubidium is diatomic.

Video Diatomic molecule

Molekul Heteronuklir

All other diatomic molecules are chemical compounds of two different elements. Many elements can combine to form heteronuclear diatomic molecules, depending on temperature and pressure.

Common examples include carbon monoxide (CO), nitric oxide (NO), and hydrogen chloride (HCl) gases.

Many 1: 1 binary compounds are usually not considered diatomic because they are polymers at room temperature, but they form diatomic molecules when evaporated, eg MgO, SiO, and many others.

Maps Diatomic molecule

Genesis

Hundreds of diatomic molecules have been identified in Earth's environment, in laboratories, and in interstellar space. Approximately 99% of Earth's atmosphere consists of two species of diatomic molecules: nitrogen (78%) and oxygen (21%). Natural hydrogen abundance (H ₂ ) in the Earth's atmosphere is only from the order of parts per million, but H ₂ is the most abundant diatom molecule in the universe. This interstellar medium is indeed dominated by hydrogen atoms.

src: i.ytimg.com

Molecular Geometry

src: shaunmwilliams.com

Historical sense

Diatomic elements play an important role in the explanation of the concept of elements, atoms, and molecules in the 19th century, because some of the most common elements, such as hydrogen, oxygen, and nitrogen, emerge as diatomic molecules. The original atomic hypothesis John Dalton assumes that all the elements are monatomic and that the atoms in the compound usually have the simplest atomic ratios to each other. For example, Dalton assumes a water formula to be HO, giving the oxygen atom a weight of eight times that of hydrogen instead of the modern value of about 16. As a result, confusion arises regarding atomic weights and molecular formulas for about half a century.

In early 1805, Gay-Lussac and von Humboldt demonstrated that water formed from two volumes of hydrogen and one volume of oxygen, and in 1811 Amedeo Avogadro had arrived at the correct interpretation of the composition of water, based on what is now called Avogadro's law and the assumption of elemental molecules diatomics. However, this result was largely ignored until 1860, in part because of the belief that atoms of one element would have no chemical affinity to the atoms of the same element, and also in part because of the clear exceptions to Avogadro's law which were not explained until later in terms of molecules that separates.

At the Karlsruhe Congress of 1860 on atomic weights, Cannizzaro evoked Avogadro's ideas and used them to produce a consistent table of atomic weights, most of which agree with modern values. This weight is an important prerequisite for the discovery of periodic law by Dmitri Mendeleev and Lothar Meyer.

src: i.ytimg.com

Exciting electronic status

Diatomic molecules are usually in the lowest state or soil, which is also conventionally known as ${\ displaystyle X}$ . When a gas diatomic molecule is bombarded by energetic electrons, some molecules may be attracted to higher electronic states, such as occurs, for example, in natural aurora; high altitude nuclear explosion; and rocket-borne electron gun experiments. Such excitation may also occur when the gas absorbs light or other electromagnetic radiation. The excited condition is unstable and naturally relaxes back to the ground state. During various short time scales after excitation (usually a fraction of a second, or sometimes longer than one second if the excited state is metastable), the transition occurs from higher to lower electronic state and finally to ground state, and at each transition of the photon is transmitted. This emission is known as fluorescence. Higher electronic status is automatically named ${\ displaystyle A}$ , ${\ displaystyle B}$ , ${\ displaystyle C}$ , etc. (but this convention is not always followed, and sometimes lower-case letters and alphabetical letters are not in order of use, as in the example below). The excitation energy must be greater than or equal to the energy of the electronic state in order for excitation to occur.

Dalam teori kuantum, keadaan elektronik dari molekul diatomik diwakili oleh

${\ displaystyle ^ {2S 1} \ Lambda (v)}  ÂÂ$

di mana ${\ displaystyle S}  ÂÂ$ adalah jumlah total spin kuantum elektronik, ${\ displaystyle \ Lambda}  ÂÂ$ adalah jumlah kuantum momentum sudut elektronik total sepanjang sumbu internuclear, dan ${\ displaystyle v}  ÂÂ$ adalah bilangan kuantum getaran. ${\ displaystyle \ Lambda}  ÂÂ$ mengambil nilai 0, 1, 2,..., yang diwakili oleh simbol status elektronik ${\ displaystyle \ Sigma}  ÂÂ$ , ${\ displaystyle \ Pi}  ÂÂ$ , ${\ displaystyle \ Delta}  ÂÂ$ ,.... Sebagai contoh, tabel berikut mencantumkan keadaan elektronik umum (tanpa nomor kuantum getaran) bersama dengan energi tingkat vibrasi terendah ( ${\ displaystyle v = 0}  ÂÂ$ ) dari nitrogen diatomik (N ₂ ), gas paling melimpah di atmosfer Bumi. Di tabel, subskrip dan superskrip setelah ${\ displaystyle \ Lambda}  ÂÂ$ memberikan rincian mekanika kuantum tambahan tentang status elektronik.

Note: The "energy" unit in the above table is actually a reciprocal of the wavelength of the photon emitted in the transition to the lowest energy state. The actual energy can be found by multiplying the statistics given by the product c (the speed of light) and h (Planck constant), that is, about 1.99 ÃÆ'â € "10 ^-25 Joule meter, and then multiply with a further factor of 100 to convert from cm ^-1 to m ^-1 .

The symbol of the term molecular is a brief expression of angular momentum that characterizes the electronic quantum state of a diatomic molecule, which is the eigenstates of Hamiltonian electronic molecules. It is also convenient, and common, to represent diatomic molecules as two mass points connected by a spring without mass. The energy involved in various molecular motions can then be broken down into three categories: translational energy, rotation, and vibration.

Energy translation

Energi translasi dari molekul diberikan oleh ekspresi energi kinetik:

${\ displaystyle E_ {trans} = {\ frac {1} {2}} mv ^ {2}}  ÂÂ$

di mana ${\ displaystyle m}  ÂÂ$ adalah massa molekul dan ${\ displaystyle v}  ÂÂ$ adalah kecepatannya.

Energi rotasi

Secara klasik, energi kinetik rotasi

${\ displaystyle E_ {rot} = {\ frac {L ^ {2}} {2I}} \,}  ÂÂ$

di mana

${\ displaystyle L \,}  ÂÂ$ adalah momentum sudut

${\ displaystyle I \,}  ÂÂ$ adalah momen inersia molekul

Untuk mikroskopis, sistem tingkat atom seperti molekul, momentum sudut hanya dapat memiliki nilai diskrit tertentu yang diberikan oleh

${\ displaystyle L ^ {2} = l (l 1) \ hbar ^ {2} \,}  ÂÂ$

di mana ${\ displaystyle l}  ÂÂ$ adalah bilangan bulat non-negatif dan ${\ displaystyle \ hbar}  ÂÂ$ adalah konstanta Planck yang dikurangi.

Juga, untuk molekul diatomik saat inersia adalah

${\ displaystyle I = \ mu r_ {0} ^ {2} \,}  ÂÂ$

di mana

${\ displaystyle \ mu \,}  ÂÂ$ adalah massa molekul yang berkurang dan

${\ displaystyle r_ {0} \,}  ÂÂ$ adalah jarak rata-rata antara pusat dari dua atom dalam molekul.

Jadi, dengan mengganti momentum sudut dan momen inersia menjadi E _membusuk , tingkat energi rotasi molekul diatomik diberikan oleh:

${\ displaystyle E_ {rot} = {\ frac {l (l 1) \ hbar ^ {2}} {2 \ mu r_ {0} ^ {2}} } \ \ \ \ \ \ l = 0,1,2,... \,}  ÂÂ$

Energi vibrasi

Tipe lain dari gerakan molekul diatomik adalah setiap atom berosilasi - atau bergetar - sepanjang garis yang menghubungkan dua atom. Energi getaran kira-kira sama dengan osilator harmonik kuantum:

${\ displaystyle E_ {vib} = \ kiri (n {\ frac {1} {2}} \ right) \ hbar \ omega \ \ \ \ \ n = 0, 1,2,.... \,}  ÂÂ$

di mana

${\ displaystyle n}  ÂÂ$ adalah bilangan bulat

${\ displaystyle \ hbar}  ÂÂ$ adalah konstanta Planck yang berkurang dan

${\ displaystyle \ omega}  ÂÂ$ adalah frekuensi sudut dari getaran.

Perbandingan antara jarak energi rotasi dan getaran

The distance, and energy of a typical spectroscopic transition, between the vibrational energy levels are about 100 times greater than the typical transition between the rotational energy levels.

src: chem.libretexts.org

Hund Cases

Good quantum numbers for diatomic molecules, as well as estimates of good rotational energy levels, can be obtained by modeling molecules using Hund cases.

src: i.ytimg.com

See also

• Diatomic molecular symmetry
• AX Method
• Octatomic Elements
• Covalent bond
• Industrial gas

src: wps.prenhall.com

References

src: wps.prenhall.com

Further reading

• Huber, K. P.; Herzberg, G. (1979). Molecular Spectrum and Molecular Structure IV. The constant of Diatomic Molecules . New York: Van Nostrand :. Reinhold Ã,
• Tipler, Paul (1998). Physics For Scientists and Engineers: Vol. 1 (4th ed.). W. H. Freeman. ISBNÃ, 1-57259-491-8 Ã,

src: images.slideplayer.com

External links

• Hyperphysics - Rotating Spectrum of Rigid Molecular Rotor
• Hyperfisis - Harmonic Quantum Oscillator
• 3D Chem - Chemical, Structure, and 3D Molecules
• IUMSC - Indiana University's Molecular Structure Center

Source of the article : Wikipedia