What is a Dalton? Measuring the Building Blocks of the Universe

Have you ever wondered how scientists weigh the invisible? You can weigh yourself easily using your bathroom scales, but how do you weigh a strand of DNA, for example? Even the most precise kitchen scales would be useless, so chemists have come up with a unit that bridges our giant reality with the microscopic particle world — the dalton.

In this article, we will explore the following topics:

• The definition of the dalton and its role in modern science;
• Who is John Dalton? The fascinating life of a revolutionary chemist;
• What is Dalton’s atomic model of the atom? The core principles of John Dalton’s theory; and
• How does atomic mass function in lab measurements?

So, what did Dalton discover about the atom that changed the rules of the game? We hope you’re ready for the ride!

The dalton ($\rm{Da}$), also known as the unified atomic mass unit, is used by chemists and biologists to describe the mass of atoms and molecules.

The answer to the question “What is a dalton?” is very precise: it is exactly $1/12\rm{th}$ of the mass of an unbound neutral atom of carbon-12 in its neutral and electronic ground state.

Why use such a specific definition?

Before 1961, physicists and chemists couldn’t agree on a standard. Physicists based their measurements on oxygen-16, while chemists used “natural” oxygen (a mixture of isotopes), which resulted in massive discrepancies in the data. The scientific community eventually united around carbon-12 as the perfect compromise.

Today, $1\ \rm{Dalton}$ is approximately $1.66054 \times 10^{-27}\ \rm{kg}$. Thanks to this value, we don’t have to deal with unimaginably small numbers. Instead of saying that a water molecule weighs $2.99 \times 10^{-23}\ \rm{grams}$, we say that it’s roughly $18\ \rm{Da}$.

Before it was a unit, “Dalton” was a name. To understand the science, we must ask: Who is John Dalton?

Actually, Dalton was not originally a chemist. Born in 1766 in Eaglesfield, England, John Dalton was raised in a Quaker family. Therefore, he wasn’t allowed to attend certain universities because he was considered a “dissenter”. However, he didn’t let this fact bring him down — he led a life of self-directed learning and rigorous observation.

His original occupation was that of a meteorologist. He observed and described over 200,000 weather events spanning 57 years, meticulously recording his findings in a diary. The Earth’s atmosphere truly fascinated him. He was particularly interested in how different gases occupy the same space — this is what eventually led him to assume that gases were composed of tiny particles.

John Dalton was so devoted to the scientific community that, as a final act of dedication, he requested that his body be donated to science after his death. This act was his last contribution to studies on red-green color blindness, a condition he suffered from. He insisted that his eyes be dissected, as he thought that his inner eye fluid was tinted blue. It wasn’t. DNA analysis in 1995 confirmed he had deutan color blindness, which means that he lacked the gene for green-sensitive cones.

The Ancient Greeks had already proposed the concept of invisible particles. So, what did Dalton discover about the atom that changed everything?

Well, he didn’t just philosophise about them — he concluded that it was indeed a physical entity. He essentially made a theory a reality.

John Dalton’s atomic model, published in its entirety in 1808, was based on the law of multiple proportions and explained how elements combined in fixed mass ratios. For instance, carbon combines with oxygen to form different gases, but always in simple whole-number ratios.

Thanks to this observation, he realized that matter was composed of countable particles.

What is Dalton’s atomic model of the atom based on?

John Dalton’s atomic model is based on a few core principles:

1. Indivisibility: Dalton imagined these elementary particles — the atoms — as solid, impenetrable spheres.

2. Identity: Atoms of a given element are identical in mass and size, and differ from those of other elements.

3. Conservation: Atoms cannot be subdivided, created, or destroyed.

4. Compounds: Atoms of different elements can combine in simple ratios to form chemical compounds.

5. Reactions: Atoms can be combined, separated, or rearranged through chemical reactions.

John Dalton and his atomic theory truly revolutionized the way we approach chemistry. While working on his model, Dalton used wooden balls and hooks to visualize chemical compounds.

While we now know that atoms aren’t solid spheres and can indeed be divided through nuclear fission, John Dalton’s atomic model, without a doubt, laid the foundation for modern chemistry.

We now know what a dalton is, but how does this knowledge help in a lab?

There is a beautiful correlation between the dalton and the gram. In fact, the mass of a single molecule in Daltons is numerically equivalent to the mass of one mole of that substance in grams. For example:

• A single molecule of caffeine ($\rm C_8H_{10}N_4O_2$) has a mass of approximately $194.19\ \rm{Da}$.
• One mole of caffeine (containing exactly $6.022 \times 10^{23}$ molecules — a number explored in our article, “How Many Molecules Are There in a Mole?”), it weighs 194.19 grams.

Isn’t this quite satisfying? When you need to perform these conversions for your own experiments, an online moles to atoms calculator is an indispensable tool for navigating the stoichiometry without getting lost in the math.

The Dalton is more than just a unit of mass; it serves as a bridge between the human scale and atomic reality.

John Dalton and his atomic model live on in modern chemistry. From the simple wooden balls he used in his lectures to the high-tech mass spectrometers measuring viral capsids today, the concept remains the same: the world is built of parts, and if we can weigh them, we can understand them.