3.2.2. ATOMIC MASS

Now-a-days, IUPAC (International Union of Pure and Applied Chemistry) is an international scientific organisation which approves names of elements, symbols and units.

The International Union of Pure and Applied Chemistry, or IUPAC, is responsible for standardizing chemical nomenclature. This ensures that all scientists around the world use the same names and symbols for chemical elements, which promotes clear communication in science.

Think of IUPAC as a global committee that agrees on a common language for all chemists, just like how countries have a common language for diplomacy. Imagine if each country had their own words for ‘peace’—communication would be a lot harder!

According to him, each element had a characteristic atomic mass. The theory could explain the law of constant proportions so well that scientists were prompted to measure the atomic mass of an atom.

Dalton's atomic theory proposed that each element has a specific atomic mass, which is a measure of how heavy an atom of that element is compared to the standard of carbon-12. This property helps in understanding how atoms combine in chemical reactions, giving rise to the law of constant proportions.

Imagine baking a cake using exact measurements—different amounts of flour and sugar based on their weights. Similarly, knowing the atomic mass of elements allows chemists to combine them in precise ratios to form compounds.

Since determining the mass of an individual atom was a relatively difficult task, relative atomic masses were determined using the laws of chemical combinations and the compounds formed.

To measure atomic masses, scientists did not attempt to weigh single atoms directly because it was too challenging. Instead, they used the masses of compounds formed from these atoms in reactions to calculate how heavy individual atoms were relative to one another.

Think of how you might calculate the weight of individual candies based on a full bag. If you know the total weight of the bag and how many candies are inside, you can find out the average weight of one candy.

Suppose we define the atomic mass unit (earlier abbreviated as ‘amu’, but according to the latest IUPAC recommendations, it is now written as ‘u’) as equal to the mass of one carbon atom, then we would assign carbon an atomic mass of 1.0 u and oxygen an atomic mass of 1.33 u.

The atomic mass unit (u) is a standard unit that reflects the mass of an atom. The carbon-12 isotope was chosen as a standard, meaning that its mass is defined as exactly 12 u. Other elements' masses are then calculated relative to this standard, simplifying comparisons between different elements.

Imagine using your friend’s weight as a baseline to compare weights of everyone else at a party. If your friend weighs 60 kg and you weigh 70 kg, you can say your weight is 10 kg heavier than your friend—this is similar to how scientists measure atomic masses.

In 1961 for a universally accepted atomic mass unit, carbon-12 isotope was chosen as the standard reference for measuring atomic masses. One atomic mass unit is a mass unit equal to exactly one-twelfth (1/12th) the mass of one atom of carbon-12.

The choice of carbon-12 as a standard reference helped to create a common ground for measuring atomic masses. This means that all other atomic masses can be expressed as fractions or multiples of the mass of carbon-12. This standardization allows scientists to communicate more easily about atomic masses.

Think about how we refer to currencies in terms of dollars or euros. If you know how many euros equal one dollar, you can convert any amount easily. Similarly, having a standard atomic mass makes it much easier for chemists to compare and calculate.

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