Atomic Theory – 101 Continued…. | Confused By The World

Atomic Theory – 101 Continued….

Mass confusion….LOL pun….

Take a deep breath, relax…. And we shall continue with our endeavour into the complex world of particle physics. So a quick recap for those whose scroll button is broken. Atomic theory was first proposed by the Ancient Greek Atomists. They first theorised that the world contained minute ‘uncuttable’ particles called atoms. These atomos along with the ‘void’ comprised the universe. This theory was later expanded upon by Islamic philosophers who further suggested that atoms were not subject to decay or change and that they contained even smaller indivisible particles.

Greek MC Hammer - Can't cut this....

It wasn’t until the 19th century that modern atomic theory began to take shape. In the 1900’s John Dalton proposed that each individual element was composed by one form of unique atoms, i.e Carbon was composed of Carbon atoms, Helium from Helium atoms. Dalton suggested that these unique atoms where immutable and unchangeable, but that they could combine with others to form complex molecules. Through his research, Dalton helped substantiate several laws of chemistry that were vital to understanding and discovery of atomic theory.

1) Law of conservation of mass – This theory was first proposed by Antoine Lavoisier in 1789. The law states that the total mass in a chemical reaction will remain constant, and that the total mass of the reactants will have the same mass of the product. So essentially if you mix in the ratio of 1 Carbon to 2 of Oxygen then, if the reaction is engineered correctly, the amount of CO2 will equal the mass of both the Carbon and Oxygen used. The ratio of 1:2 is used because you need 2 atoms of Oxygen per 1 atom of Carbon to make CO2. This law suggested to Dalton that matter was essentially indestructible as no apparent mass is lost during the reaction.

2) Law of definite proportions – This theory was first proven by Joseph Louis Proust in 1799. This law argues that if a compound is broken down into its constituent elements, then the masses of the constituents will always have the same proportions, regardless of the quantity or source of the original substance. So again if we break down a gram of H20 then the law states that we will receive amounts of Hydrogen and Oxygen in a ratio of 2:1.

Using and expanding upon these two laws Dalton proposed a 3rd law entitled the law of multiple proportions. This law states that if two elements form more than one compound between them, then the ratios of the masses of the second element which combine with a fixed mass of the first element will be ratios of small integers.

Dalton formulated his law by doing experiments with Nitrous Oxide (NO) and Oxygen (O2). By using these two molecules you can through chemical processes make 2 separate compounds. The first compound you can make is Nitrogen Dioxide (NO2), the second more complex compound is Dinitrogen Trioxide (N2O3). Dalton experimented with different amounts of NO and 2 separate processes. He discovered that when he mixed;

2 NO + 4 O2 = 2 NO2 – this experiment gave him the mix ratio of 1:2, 1 part NO to
2 parts O2.

In the second experiment he mixed;

4 NO + O2 = 2 N2O3 – this experiment gave him a mix ratio of 2:1, as you can see
there are 6 atoms of Oxygen and 4 of Nitrogen.

Using these newly tested and formulated laws, Dalton estimated the atomic weights according to the mass ratios that he discovered. However, Dalton was unaware that some elements like Oxygen actually exist as a molecule in the form of O2. This mistake was later corrected by Amedeo Avogadro.