AAT Bioquest

What are the general principles of Dalton's atomic theory?

Posted December 13, 2022


Dalton’s atomic theory is made up of five principles that are based on two fundamental laws -The Law of Conservation of Mass and the Law of Constant Composition.

Principle 1: All matter is made of particles called atoms - Dalton proposed that all matter is made up of tiny particles called atoms. He imagined atoms as hard, solid, impenetrable particles. He hypothesized that the two laws - conservation of mass and constant composition – could be explained using his explanation of atoms. 

Principle 2: Atoms are indivisible and indestructible - According to Dalton’s atomic theory, atoms are the smallest particles that occur naturally. They cannot be created, destroyed, or divided into smaller particles. 

Principle 3: All atoms of a particular element are identical in mass and properties - In the third part of Dalton’s atomic theory, he noted that every atom of an element is the same as every other atom of that element. For example, all atoms in carbon are identical to each other. Also, the atoms of one element are unique to that element and are different from the atoms of all other elements. According to this theory, a carbon atom is completely different from an oxygen or sodium atom. Different elements may share some characteristics but no two elements have the exact same set of properties.  

Principle 4: Atoms of different elements combine with each other in fixed whole-number ratios to form compounds - The fourth principle states that compounds are essentially combinations of two or more atoms of different types. An example is water or H20. Water is a combination of two separate elements – hydrogen (H) and oxygen (O). Each of these elements has a unique set of physical and chemical properties. When they react with each other, the atoms combine in a 1:2 ratio to form water. 

Principle 5: Atoms may be combined, separated or rearranged in a chemical reaction - In this fifth and final part of Dalton's atomic theory, he suggested that chemical reactions merely rearrange atoms to create new products. They don't destroy existing atoms or create new atoms. For example, in the reaction between sodium (Na) and chlorine (Cl), the atoms simply rearrange to form a new compound NaCl or salt.  However, both sodium and chlorine atoms still exist in the new compound. 

Additional resources

John Dalton's "Aha" Moment: the Origin of the Chemical Atomic Theory

ReadiUse™ Tyramide (TSA)/Styramide (PSA) Optimized Reaction Buffer