TEORI ATOM(Munculnya Kimia Modern)

PendahuluanKonsep tentang atom sebenarnya sudah ada sejak jaman Yunani Kuno.Konsep itu kemudian timbul tenggelam sampai abad pertengahan.Dengan banyaknya eksperimen tentang gas dan vakum sesudah Galileo (misalnya oleh Torricelli [pernah menjadi murid Galileo] tentang kolom air raksa yang ditahan tekanan udara 1 atmosfer) maka teori atom menjadi mengemuka untuk memberikan penjelasan.

As we have seen, the atomistic hypothesesup to the nineteenth century had not given riseto an unambiguous and precise theory either ofmatter or of heat. [Teori atom belum menjadi paradigma.]

Yet, between the publicationof Robert Boyle's Sceptical Chymist in 1661 andLavoisier's death in 1794 [dengan pisau guillotine !], there had developed a fundamental concept that was destined to givea new, vital, and precise meaning to the speculativeatomistic hypothesis. This concept wasthe chemical element. [Munculnya kimia modern]

Teori atom kemudian mendapatkan dukungan yang kuat dengan munculnya konsep unsur kimia.

Munculnya teori atom sudah diawali pada jaman kuno, namun diterimanya sebagai paradigma bersamaan dengan munculnya kimia modern. Teori atom diperlukan bagi perkembangan kimia (terutama tentang reaksi kimia, bidang garapan utama ilmu kimia).

By the end of the eighteenth century, chemistshad come to accept this operational definition ofelement: It is a substance that cannot be decomposedinto other substances by chemical or physicalmeans available at the present time.

Whether these elements would in the future turn out to bereally compounds of yet more basic substanceswas a question that could safely be left to metaphysicians, or to future scientists.

Teori atom yang pertama sekali cukup komprehensif adalah oleh Dalton.

Perhatikan judul bukunya :A New System of Chemical Philosophy.

a) Each particle of a gas is surrounded by anatmosphere of caloric.

b) The particles are essentially at rest, their shellsof caloric touching. Throughout,Dalton accepts the notion that the only means forthe action of forces among atoms is direct contact.He is as uncomfortable with the notion ofaction at a distance as Newton's contemporarieshad been.

c) The total diameter of each particle, includingthe caloric atmosphere or shell, differs from onesubstance to the next

Dalam teori atom Dalton tidak ada ruang kosong antar atom.

Ruangan antar atom terisi caloric, sesuatu yang mengisi ruang dan berkaitan dengan gejala-gejala yang menyangkut panas.

Perumusan Atom Dalton dalam bahasa modern

a) Matter consists of indivisible atoms.

b) Atoms are unchangeable.

c ) Compounds are made of molecules.

d) All atoms or molecules of a pure substance are identically alike.

e) In chemical reactions, atoms are only rearranged,not created or destroyed.

Fakta :No matter in which locality apure substance-say a metallic oxide, a drop ofsome liquid, or a complex gas-is found, nomatter whether it is artificially prepared or takenfrom a natural source, the proportions by weightof the constituent elements in every case arealways the same.

Hukum Ketetapan Proporsi : In forming molecules during chemicalreactions, the numbers of combining atomsof the different elements form simple, definiteratios.

Kontribusi Dalton :a) As we saw, Dalton's chemical atom is the conceptthat gives physical meaning to the law ofconservation of mass, and that integrates it withthe law of definite proportions.

b) Perhaps the best support of the atomic theory,by common consent at the time, was an extraordinarilypowerful insight for the later progressof chemistry. Terutama dalam pengembangan notasi untuk reaksi kimia yang merupakan hal yang sangat penting {indispensable] bagi perkembangan kimia sampai saat ini.

Setelah mengalami pengembangan oleh berbagai ilmuwan lain, misalnya Gay-Lussac, maka Teori Atom mendapatkan bentuknya seperti yang sekarang, terutama dalam model gas, berkat gagasan dari Avogadro.

a) As had been often and persistently suggestedby Gay-Lussac and others, Dalton's picture of agas in which the particles are in contact is nowreplaced by another (it does not matter at thispoint whether a static or a kinetic model), inwhich the particles have only a very thin shell ofcaloric and are quite small compared with the distancesbetween them.

Dalton : Atom-atom saling bersinggungan, harus selalu kontak satu sama lain.Avogadro : Atom-atom ukurannya sangat kecil dibandingkan jaraknya satu sama lain. Antar atom adalah ruang kosong.

b) Contrary to initial considerations of simplicity,or to the firm faith of Dalton, or, in fact, to everyreasonable expectation at the time,

the ultimateparticles of gaseous elements are conceived to benot necessarily just single solitary atoms, butinstead may be thought of as being made up of twoor more chemically alike atoms "united by attractionto form a single whole. " Calling the smallestsuch unit a molecule - - - - > munculnya konsep molekul

Hukum Avogadro :

Equal volumesof all gases, whether elements or compounds,or even mixtures, contain equal numbersof molecules.

Satu mol sembarang gas volumenya sama dan mengandung cacah molekul atau atom yang sama.Volume = 22,4 literBilangan = NA (Bilangan Avogadro, ordenya 10^23)

Avogadro was not the first scientist to proposeit, but he did succeed in incorporating it into acoherent and convincing theory.

b) He replaced the static model, in which atomsare in contact and fill up all the available space,with another model in which the molecules (possibly containing two or more atoms) are quite small compared to the spaces between them.

Avogadro mengubah model statik dari Dalton menjadi bentuk model atom dari gas seperti yang sekarang.

Experiments in manyseparate branches of physical science since thattime have indirectly produced values, and theyall agree fairly well on about 2.69 x 10^19 molecules/cm^3 of any gas at O°C and atmosphericpressure.

As will be noted in Section 22.7, thisis now called Loschmidt's number in honor of thescientist whose work led to the first accurateestimate of its value.

Bedakan bilangan Avogadro dengan bilangan Loschmidt, meskipun keduanya merujuk hal yang sama. Bedanya adalah faktor 22.4*10^4. Jelaskan faktor itu !

Inilah definisi satu mol :A more useful number is the number ofmolecules whose mass in grams is the same asthe weight of one of those molecules relative tothe hydrogen atom-for example, the numberof molecules in a 32-gram sample of pure oxygen,if the molecular weight of oxygen is 32.

This quantity is called the "mole “. Avogadro's hypothesis states that the numberof molecules in a mole is the same for anygas, and this number is therefore called Avogadro'snumber, even though he did not knowits value.Bil. Avogadro tidak ditemukan Avogadro, sedangkan bil. Loschmidt memang ditemukan dia.

Rangkuman

Kita sudah membahas Teori Atom pertama yg komprehensif yaitu dari Dalton dan perubahannya sampai jadi bentuknya yg seperti sekarang oleh Avogadro dan bagaimana Teori Atom itu bisa menjadi paradigma karena diperlukan bagi tumbuhnya ilmu kimia sehingga memisahkan diri dari natural philosophy.