Explain your Yes or No answer in Question 4 The atomic theory has changed over time.

The atomic theory has indeed changed over time, and I would answer "Yes" to this question. The atomic theory is not static; it has evolved significantly since its inception.

1. Historical Development: The concept of the atom originated with ancient philosophers like Democritus, who proposed that matter is made up of indivisible particles. However, this idea lacked scientific evidence.

2. John Dalton's Contribution: In the early 19th century, John Dalton formulated a more structured atomic theory based on experimental data. He proposed that each element consists of identical atoms and that chemical reactions involve the rearrangement of these atoms.

3. J.J. Thomson's Discovery: In the late 19th century, J.J. Thomson discovered electrons, leading to the realization that atoms are not indivisible. This prompted the development of the "plum pudding model," where electrons were thought to be embedded within a positively charged "soup."

4. Rutherford and the Nucleus: Ernest Rutherford's gold foil experiment in 1909 refuted Thomson’s model, leading to the discovery of the atomic nucleus and the realization that most of an atom’s volume is empty space.

5. Quantum Mechanics: The 20th century saw the advent of quantum mechanics, profoundly changing the understanding of atomic behavior. Scientists like Niels Bohr and later quantum physicists expanded upon the notion of orbits and electron clouds, offering a probabilistic view of atomic structure.

6. Current Understanding: Today’s atomic theory incorporates concepts of subatomic particles (protons, neutrons, and electrons), quantum fields, and the standard model of particle physics, acknowledging that atoms are complex and dynamic entities.

In conclusion, the atomic theory has undergone substantial changes reflecting advancements in scientific understanding, experimental techniques, and theoretical developments over centuries.