1.3 Use the models to explain how and why the model of the atom changed over time as new evidence arose.

What was Dalton’s claim about the atom?

Dalton claimed that atoms are indivisible particles that combine in fixed ratios to form compounds.

What evidence supported Dalton’s atomic model?

Dalton observed that substances combine in fixed ratios during chemical reactions, supporting the idea that matter is made of discrete, indivisible atoms.

Why was Dalton’s atomic model replaced?

Dalton’s model couldn’t explain the electrical properties of matter or the internal structure of atoms. New evidence showed atoms had internal components.

What was Thomson’s claim about the atom?

Thomson claimed that atoms are made of positively charged “pudding” with negatively charged electrons embedded inside.

What evidence supported Thomson’s model of the atom?

Thomson discovered electrons using cathode ray tubes, showing that atoms contain negatively charged particles.

Why was Thomson’s atomic model replaced?

Thomson’s model couldn’t explain why atoms were stable or how they emitted certain types of radiation. New experiments suggested that atoms had a dense central region (nucleus).

What was Rutherford’s claim about the atom?

Rutherford claimed that atoms have a small, dense, positively charged nucleus at the center, with electrons orbiting around it.

What evidence supported Rutherford’s model of the atom?

Rutherford’s gold foil experiment showed that most alpha particles passed through the foil, but some were deflected at larger angles, indicated a small, dense, positively charged nucleus in the atom.

Why was Rutherford’s atomic model a change from Thomson’s?

Rutherford’s model explained the deflections of alpha particles, showing that atoms have a dense nucleus, which Thomson’s model could not explain.