Atomic theory is the scientific theory which defines the nature and behavior of matter. Matter is composed of different units known as atoms. It started as a philosophical concept in ancient period and entered to science mainstream in the early 19th century. Several discoveries in chemistry field showed that matter did behave as if it were made up of atoms.
The word atom comes from Ancient Greek word “atoms” which means uncuttable. In the 19th century chemists started using the term in connection with the growing number of chemical elements that are irreducible. In the 20 century, through several experiments with radioactivity and electromagnetism. Scientists discovered that uncuttable atoms is a mixture of several subatomic particles which exists separately from each other. At a certain extreme environment, neutron stars, extreme pressure and temperature prevents these uncuttable atoms from existing. As atoms were found to be divisible, physicists invented a term, “elementary particles”.
Dalton’s Atomic Theory:
According to Dalton’s atomic Theory,
- Every chemical element is composed up of small particles that are indivisible and cannot be seen by the naked eye are defined as atoms.
- Atoms are indestructible as ” atoms can neither be created nor destroyed.”
- All the atoms of an element are identical in mass and other properties while atoms of one element differ from all the other elements. For Example- Silver and Gold have different atomic masses and different properties.
- Compounds are formed by a combination of different elements in a simple numerical ratio.
- Any chemical reaction is an arrangement of atoms.
Rutherford Atomic Theory:
According to the Rutherford atomic theory, an atom is the most empty space with electrons having a fixed orbit and positively charged nucleus. Ernest Rutherford has a native in New Zealand and worked at University of Manchester in England in early 1900s. He spent most of his academic career in researching for radioactivity. He won the Nobel Prize for his discoveries for radioactivity in 1908. After this, he started developing the atom model.
In 1909, Rutherford started his famous gold foil experiment in which his colleague Hans Geiger bombarded a small piece of gold foil with positively charged alpha particles. In this experiment, they were expecting those particles to travel straight through the foil. There were many alpha particles that ricocheted off the foil which suggest that there was something very positive that these particles were colliding with. Both of them named the positive force as nucleus and based on this the Rutherford model was created.
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