Question

history of the atom chemistry
name:
launch
each of these scientists contributed to our current understanding of the atom. match the scientist to their discovery/discoveries:
niels bohr
ernest rutherford
john dalton
j j thomson
james chadwick
elements are made from solid spheres.
atoms contain negative particles called electrons.
atoms have a positive nucleus.
electrons orbit the nucleus in fixed shells.
the nucleus contains particles called protons.
the nucleus also contains neutrons.
main stage
plum pudding model
describe j j thomson’s plum pudding model of an atom and explain what would happen if alpha particles were fired at atoms (according to the model).
rutherford’s alpha particle scattering experiment showed that the plum pudding model was incorrect therefore rutherford came up with the nuclear model of an atom. complete the explanations below:
during the experiment most of the alpha particles passed straight through the gold sheet which shows that ……………………………………………………
very few particles were deflected which suggests that ……………………………………………………
rutherford’s nuclear model
boost

1. where is most of the mass of an atom concentrated?
2. why was the plum pudding model replaced with the nuclear model?
3. why did niels bohr suggest that electrons orbit at fixed distances?

landing
below is a table showing different properties of the atom. number the statements to show the order in which they were discovered:
electron shells
protons
electrons
neutrons
positive atomic nucleus

Explanation:

• Launch: John Dalton - Elements are made from solid spheres. J J Thomson - Atoms contain negative particles called electrons. Ernest Rutherford - Atoms have a positive nucleus. Niels Bohr - Electrons orbit the nucleus in fixed shells. James Chadwick - The nucleus also contains neutrons.
• Main Stage - Plum pudding model: J J Thomson's Plum pudding model proposed that an atom is a uniform positive - charged sphere with electrons embedded in it like plums in a pudding. If alpha particles were fired at atoms according to this model, they would pass straight through as the positive charge was thought to be evenly distributed and not concentrated enough to repel the alpha particles significantly.
• Main Stage - Rutherford's experiment: Most of the alpha particles passed straight through the gold sheet which shows that most of the space inside an atom is empty. Very few particles were deflected which suggests that the positive charge and most of the mass of the atom are concentrated in a very small space (the nucleus).
• Boost:

1. Most of the mass of an atom is concentrated in the nucleus.
2. The plum pudding model was replaced with the nuclear model because Rutherford's alpha - particle scattering experiment showed results that could not be explained by the plum pudding model. The plum pudding model predicted that alpha particles would pass straight through the atom with little to no deflection, but in reality, some alpha particles were deflected at large angles, indicating a concentrated positive charge (the nucleus).
3. Niels Bohr suggested that electrons orbit at fixed distances to explain the stability of atoms and the discrete line spectra of elements. According to classical physics, electrons moving in circular orbits should continuously emit radiation and spiral into the nucleus. Bohr's model proposed that electrons could only occupy certain discrete energy levels or orbits, preventing this collapse.

• Landing: The order of discovery: Electrons (J J Thomson), Positive atomic nucleus (Ernest Rutherford), Protons (Eugen Goldstein, but Rutherford's work was important in understanding the nucleus which contains protons), Electron shells (Niels Bohr), Neutrons (James Chadwick). So the order is 3, 4, 1, 5, 2.

Answer:

• Launch: John Dalton - Elements are made from solid spheres; J J Thomson - Atoms contain negative particles called electrons; Ernest Rutherford - Atoms have a positive nucleus; Niels Bohr - Electrons orbit the nucleus in fixed shells; James Chadwick - The nucleus also contains neutrons.
• Main Stage - Plum pudding model: The atom is a uniform positive - charged sphere with electrons embedded in it. Alpha particles would pass straight through as the positive charge is evenly distributed.
• Main Stage - Rutherford's experiment: Most of the space inside an atom is empty; the positive charge and most of the mass of the atom are concentrated in a very small space (the nucleus).
• Boost:

1. In the nucleus.
2. Because Rutherford's alpha - particle scattering experiment results contradicted the plum pudding model.
3. To explain atomic stability and discrete line spectra.

• Landing: 3, 4, 1, 5, 2.