Dalton’s Atomic Theory – An Approach to Atom

An English Scientist named John Dalton worked about 200 years ago on the origin of gases and chemical compounds. As a result of observations he made during his experiments, he published a groundbreaking theory on the nature of matter. Dalton’s model succeeded in describing essential findings like the law of constant composition.

On the other hand, Henry’s law is one of the gas laws, which states that the amount of gas usually taken to mean the mass of the gas that is dissolved in a liquid is directly proportional to the pressure of the gas above the solution. Simply, Henry’s law described the solubility of gas in a liquid. This law was described in 1801 by William Henry (1774-1836), who was an English Chemist and Physician.

Postulates of Dalton’s Atomic Theory

The hypothesis that all matter consists of very small, indivisible particles (atoms) is called atomic theory of matter. Dalton’s theory of atomics was based on the law of chemical combination. For example, the postulate of Dalton’s Atomic Theory that “atoms can neither be created nor destroyed” was the result of the law of conservation of mass given by Lavoisier.

The main postulates of this theory can be stated as follows.

  • Elements are composed of small particles, called atoms.
  • The atoms of a particular element vary from those of any other element.
  • All the atoms are identical to a given element.
  • To form compounds, atoms of one element interact with atoms of other elements. A given compound always has equal relative numbers and atom types.
  • In chemical processes, atoms are indivisible. That is, in chemical reactions atoms are neither created nor destroyed. A chemical reaction essentially changes the arrangement of the atoms.

Application of Henry’s Law

Henry’s law provides a relationship between a solute’s vapor pressure and its mole fraction in a mixture, and is the basis for determining an ideal dilute solution. An ideal dilute solution is a solution that obeys Henry law at low concentration of the solute and for which the solvent obeys Raoult’s law. A common formula used today for Henry’s law is

P = k × C

Where P is the partial pressure of the particular gas and C is the concentration of the dissolved gas and k is Henry’s law constant.

Knowledge of Henry’s law constants for gases in blood and fats is important for the discussion of respiration, especially when the partial pressure of oxygen is abnormal as in driving and mountaineering and for the discussion of the action of gaseous anesthetics. Henry’s law is used to determine the volatilization of dissolved gases during remedial operations.

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