According to Dalton's atomic theory, atoms are indivisible and indestructible particles that make up all matter in the universe. This theory, proposed by John Dalton in the early 19th century, laid the foundation for modern atomic theory and revolutionized our understanding of the structure of matter.

Key Points of Dalton's Atomic Theory:

1. Atoms are indivisible: According to Dalton, atoms are the smallest, indivisible particles of matter. They cannot be broken down into smaller components through chemical reactions. This concept was later modified with the discovery of subatomic particles such as protons, neutrons, and electrons.

2. Atoms are indestructible: Dalton believed that atoms were indestructible and retained their identity during chemical reactions. While this concept is generally true for most chemical reactions, nuclear reactions can break apart atoms and convert mass into energy.

3. Atoms of the same element are identical: Dalton proposed that all atoms of the same element are identical in size, mass, and chemical properties. This assumption holds true for most elements, but isotopes, which have different numbers of neutrons, can exist for some elements.

4. Atoms combine in whole number ratios: Dalton stated that atoms combine to form compounds in simple, whole number ratios. This concept is known as the law of multiple proportions and is still valid today.

Composition of Atoms:

While Dalton's atomic theory laid the groundwork for our understanding of atoms, subsequent discoveries have revealed a more complex structure. Atoms are composed of subatomic particles, including protons, neutrons, and electrons.

1. Protons: Protons are positively charged particles found in the nucleus of an atom. They have a mass of approximately 1 atomic mass unit (amu).

2. Neutrons: Neutrons are neutral particles also located in the nucleus of an atom. They have a mass similar to protons, approximately 1 amu.

3. Electrons: Electrons are negatively charged particles that orbit the nucleus in energy levels or shells. They have a significantly smaller mass compared to protons and neutrons.

Conclusion:

In summary, according to Dalton's atomic theory, atoms are indivisible and indestructible particles that make up all matter. While Dalton's theory provided a solid foundation for understanding the basic properties of atoms, subsequent discoveries have revealed a more detailed structure involving subatomic particles such as protons, neutrons, and electrons.