Name: dalton’s laws and early atomic ideas
Uploaded: 2020-09-03T13:38:25.000Z
Duration: 2 min 59 s
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K12 Standards

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North Carolina K-12 Science Standard Course of Study

9-12

Chemistry

Matter and its Interactions

PS.Chm.1.1

The Atomic Theory of Matter

Gli antichi greci come Democrito avanzarono per primi l'idea di atomos, come la più piccola unità indivisibile di materia. Questa idea è stata successivamente presentata come Teoria Atomica dallo scienziato inglese John Dalton. Il primo postulato della teoria atomica di Dalton suggerisce che gli elementi siano composti da minuscole particelle indivisibili chiamate atomi.

Per esempio, l'idrogeno è costituito da due atomi di idrogeno legati insieme e l'ossigeno è costituito da due atomi di ossigeno legati insieme. Il secondo postulato afferma che mentre gli atomi dello stesso elemento sono identici, differiscono dagli atomi di altri elementi. Pertanto, tutti gli atomi di idrogeno sono identici tra loro, ma differiscono dagli atomi di ossigeno.

Il terzo postulato afferma che atomi di elementi diversi possono combinarsi tra loro, in semplici rapporti di numeri interi, per formare composti. Per esempio, due atomi di idrogeno e un atomo di ossigeno si combinano in un rapporto di 2 a 1 per formare H2O:acqua. L'ultimo postulato della teoria di Dalton afferma che le reazioni chimiche non cambiano gli atomi di un elemento in atomi di un elemento diverso;gli atomi esistenti si riorganizzano invece, per formare nuove sostanze.

Durante la formazione dell'acqua, gli atomi di idrogeno e ossigeno esistenti non vengono né creati né distrutti, ma si riorganizzano. Dalton costruì la sua teoria atomica su due leggi precedenti delle reazioni chimiche:la legge di conservazione della massa e la legge delle proporzioni definite. La legge di conservazione della massa afferma che la massa totale prima e dopo una reazione chimica rimane costante.

Dunque, 18 grammi di acqua si scompongono in 2 grammi di idrogeno e 16 grammi di ossigeno. La legge delle proporzioni definite afferma che, indipendentemente dalla fonte, in un dato composto chimico, il rapporto di massa degli elementi costituenti rimane sempre fisso. Pertanto, un campione di acqua pura avrà sempre un rapporto di massa da 1 a 8 tra idrogeno e ossigeno, indipendentemente dalla massa totale dell'acqua.

Dalton quindi propose la legge delle proporzioni multiple basata sulla sua teoria. Secondo questa legge, quando due elementi si combinano per formare più di un composto, masse diverse di un elemento si combinano con la massa fissa dell'altro elemento in un piccolo rapporto di numeri interi. Pertanto, una massa fissa di idrogeno, 2 grammi, si combina con diverse masse di ossigeno, 32 o 16 grammi, in un piccolo rapporto di numeri interi di 2 a 1, per formare due diversi composti:perossido di idrogeno e acqua.

la teoria atomica della materia

La prima discussione documentata sulla struttura di base della materia proviene dagli antichi filosofi greci. Leucippo e Democrito sostenevano che tutta la materia era composta da piccole particelle finite che chiamavano atomos, che significa “indivisibile”. Successivamente Aristotele e altri giunsero alla conclusione che la materia consisteva di varie combinazioni dei quattro “elementi”: fuoco, terra, aria e acqua, e poteva essere divisa all’infinito. È interessante notare che questi filosofi consideravano gli atomi e gli “elementi” come concetti filosofici, ma a quanto pare non presero mai in considerazione l’idea di eseguire esperimenti per testare le loro idee.

La visione aristotelica della composizione della materia prevalse per oltre duemila anni fino a quando lo scienziato inglese John Dalton rivoluzionò la chimica con la sua ipotesi che il comportamento della materia potesse essere spiegato utilizzando una teoria atomica. Pubblicate per la prima volta nel 1807, molte delle ipotesi di Dalton sulle caratteristiche microscopiche della materia sono ancora valide nella moderna teoria atomica.

Ecco i postulati della teoria atomica di Dalton:

<ol>
	<li>La materia è composta da particelle estremamente piccole chiamate atomi. Un atomo è l'unità più piccola di un elemento che può partecipare a un cambiamento chimico.</li>
	<li>Un elemento è costituito da un solo tipo di atomo, avente una massa caratteristica dell'elemento che è la stessa per tutti gli atomi di quell'elemento. Un campione macroscopico di un elemento contiene un numero incredibilmente elevato di atomi, che hanno tutti proprietà chimiche identiche.</li>
	<li>Gli atomi di un elemento differiscono nelle proprietà dagli atomi di tutti gli altri elementi.</li>
	<li>Un composto è sostituito da atomi di due o più elementi combinati in un piccolo rapporto di numeri interi. In un dato composto il numero di atomi di ciascuno dei suoi elementi è sempre presente nello stesso rapporto.</li>
	<li>Gli atomi non vengono né creati né distrutti durante un cambiamento chimico, ma vengono invece riorganizzati per produrre sostanze diverse da quelle presenti prima del cambiamento. </li>
</ol>

Dalton usò le leggi delle reazioni chimiche come base per la sua teoria: (1) La legge della conservazione della massa, (2) La legge delle proporzioni definite e (3) La legge delle proporzioni multiple. La teoria atomica di Dalton fornisce una spiegazione microscopica delle numerose proprietà macroscopiche della materia.

La legge della conservazione della massa fu scoperta dal chimico francese Antoine Lavoisier. Egli affermò che gli atomi non vengono né creati né distrutti durante un cambiamento chimico; la massa totale della materia presente quando essa cambia da un tipo all'altro rimane costante.

Dalton conosceva anche gli esperimenti del chimico francese Joseph Proust, il quale dimostrò che tutti i campioni di un composto puro contengono gli stessi elementi nella stessa proporzione in massa. Quest’affermazione è nota come legge delle proporzioni definite o legge della composizione costante. L'ipotesi che il numero degli atomi degli elementi di un dato composto esista sempre nello stesso rapporto è coerente con queste osservazioni.

Dalton utilizzò anche i dati di Proust, nonché risultati dei suoi stessi esperimenti, per formulare un'altra legge interessante. La legge delle proporzioni multiple afferma che quando due elementi reagiscono per formare più di un composto, la massa fissa di un elemento reagirà con le masse degli altri elementi in un rapporto di numeri piccoli e interi.

La teoria di Dalton fornì un quadro che fu successivamente ampliato per dimostrare che l’atomo è composto da particelle subatomiche, gli atomi di uno stesso elemento possono differire in massa e sono noti come isotopi.

Questo testo è adattato da <a href="https://openstax.org/books/chemistry-2e/pages/2-1-early-ideas-in-atomic-theory">Openstax, Chemistry 2e, Section 2.1: Early Ideas in Atomic Theory. </a>

La teoria atomica della materia

La prima discussione documentata sulla struttura di base della materia proviene dagli antichi filosofi greci. Leucippo e Democrito sostenevano che tutta la materia ...

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dalton’s laws and early atomic ideas

Dalton’s atomic theory explains matter with atoms, elements, and compounds. It also shows how chemical changes follow simple laws. This idea gave chemistry a microscopic model for what can be seen in the lab.

The earliest recorded ideas about matter came from ancient Greek philosophers. Leucippus and Democritus said all matter was made of tiny, finite particles called atomos, meaning “indivisible.” Aristotle and others later argued that matter was made from four elements: fire, earth, air, and water. They also believed matter could be divided forever, and these ideas were treated as philosophy rather than experiments.

That view lasted for more than two thousand years. Then English scientist John Dalton changed chemistry with an atomic theory of matter. He first published it in 1807. Many of his ideas still fit modern atomic theory.

Dalton’s postulates describe matter at the atomic level. Matter is made of extremely small particles called atoms. An atom is the smallest unit of an element that can take part in a chemical change. An element contains only one type of atom, and atoms of the same element have the same characteristic mass and chemical properties. Atoms of different elements have different properties. A compound is made of atoms of two or more elements joined in a small, whole-number ratio, and the ratio stays the same in a given compound. During a chemical change, atoms are not created or destroyed. They are rearranged into new substances.

Dalton built his theory using three key laws of chemistry. The law of conservation of mass says mass stays constant during a chemical change, a result linked to Antoine Lavoisier. The law of definite proportions, also called the law of constant composition, says every pure sample of a compound contains the same elements in the same mass ratio, as shown by Joseph Proust. Dalton also used the law of multiple proportions, which says that when two elements form more than one compound, fixed masses of one element combine with the other in small whole-number ratios.

Dalton’s atomic theory gives a microscopic explanation for macroscopic matter. It also helped later scientists show that atoms contain subatomic particles. Later work also showed that atoms of the same element can differ in mass, which are called isotopes.

Dalton’s Laws and Early Atomic Ideas

the atomic theory of matter

Dalton’s atomic theory explains matter with atoms, elements, and compounds. It also shows how chemical changes follow simple laws. This idea gave chemistry a microscopic model for what can be seen in the lab. The earliest recorded ideas about matter came from ancient Greek philosophers. Leucippus and Democritus said all matter was made of tiny, finite particles called atomos, meaning “indivisible.” Aristotle and others later argued that matter was made from four elements: fire, earth, air, and...

subatomic particles

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Explore Dalton’s atomic theory, the laws of conservation of mass, definite proportions, and multiple proportions, plus the early ideas that shaped modern chemistry.

Dalton’s Laws and Early Atomic Ideas | JoVE K12

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Dalton’s Laws and Early Atomic Ideas

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