Dalton’s Atomic Theory

John Dalton was a British scientist and chemist known for his significant contributions to atomic theory and modern chemistry. Born in 1766 in England, Dalton had a keen interest in science from a young age. He made notable advancements in understanding the behaviour of gases and is also known for his research on colour blindness, a condition sometimes referred to as "Daltonism" in his honour.

In 1803 A.D., Dalton introduced his famous atomic theory. This theory was a major milestone in understanding matter and laid the groundwork for modern chemistry. Dalton proposed that all matter is made up of extremely small and indivisible particles called atoms. Atoms are the basic building blocks of all substances, similar to how bricks make up a wall.

John Dalton

Dalton proposed that everything around us is made up of tiny, invisible particles called atoms. Atoms are the fundamental building blocks of matter, similar to how bricks build a wall. He stated that atoms cannot be broken down into smaller particles or destroyed. They remain unchanged in chemical reactions, only rearranging to form new substances.

According to Dalton, all atoms of a single element are exactly the same in terms of size, mass, and chemical properties. For example, all oxygen atoms are identical to each other but different from hydrogen atoms.

• Atoms of different elements have distinct properties, such as different masses and sizes. For instance, atoms of iron are different from atoms of gold.
• Dalton observed that atoms join together in fixed, simple ratios to form compounds. For example, water (H₂O) is made of two hydrogen atoms and one oxygen atom, always in this ratio.
• In a chemical reaction, atoms are not lost or made; they are simply rearranged to form new substances. This explains the Law of Conservation of Mass, which states that mass is conserved in a chemical reaction.

Dalton's atomic model

Understanding Dalton’s Atomic Model

• Take a solid ball and a Bundi Laddu and press both with your palms.
• Observe that the Bundi Laddu breaks into small Bundis, showing it has an internal structure.
• Cut the solid ball with a knife and observe that it remains uniform inside, without any smaller components.

Compare the two:

• The Bundi Laddu represents composite objects with smaller particles.
• The solid ball represents Dalton’s model of an atom—a hard, solid sphere with no internal structure.

Conclusion:
Dalton described the atom as a solid, indivisible sphere, just like the solid ball, with mass evenly distributed and no smaller particles inside.