Models of the Atom

PLUM PUDDING MODEL

Developed as a result of discovering that a beam was attracted to a positive plate.
- Conclusion: the beam must be composed of negatively charged particles (electrons).
- Concept introduced: for every negative charge, a positive charge must coexist.
Named after a dish popular at the time, now more comparable to a chocolate chip cookie.
Description of the model:
- The atom is considered overall positive.
- Negative electrons are dispersed throughout the positive part of the atom.
- Signature feature: the magnitude and strength of the positive charge equals the sum of the negative charges.

Conducted by Ernest Rutherford, leading to significant changes in atomic theory.
Experiment comprised of a 'gold foil experiment':
- Utilized a lead box containing a radioactive substance with a hole for radiation to escape as a beam.
- Beam constituted of alpha particles, which are positively charged:
- Alpha particles are composed of the same constituents as a helium nucleus.
Setup of the experiment:
- The beam of alpha particles directed towards a sheet of gold foil.
- The gold foil was surrounded by a detecting screen, responsible for marking the impacts of alpha particles.

The behavior of the alpha particles as they interacted with the gold foil:
- Most alpha particles traveled through the foil without deflection.
- Indicates that atoms are largely empty space.
- Some alpha particles deflected at small angles.
- Very few experienced major deflection or rebounded backward.

Major inferences regarding the atomic structure based on experimental results:
- The atom is predominately empty space.
- Since alpha particles are positive, there exists a positive component within the atom itself.
- This positive component is notably small.

The Rutherford model presented inconsistencies:
- Lack of explanation for how negatively charged electrons remained in constant orbit without spiraling into the positively charged nucleus.

Niels Bohr, a quantum chemist, initiated changes to Rutherford’s atomic model.
Rethinking the model considering the attraction of positives and negatives:
- Recognized that the model lacked a neutral nucleus component, conflicting with established principles.
- Understanding required revisions to Rutherford’s framework of atomic structure.
Bohr's conceptualization of atomic structure:
- Electrons orbit the nucleus similarly to how planets orbit the sun.
- These electron paths are termed orbitals, each possessing a specific energy level known as quanta.
Electron energy levels:
- When an electron acquires energy, it moves to a higher energy orbital, referred to as the excited state.
Transition back to the ground state:
- An electron returning to its normal energy state releases energy as light, resulting in unique spectral lines for each element.
- Spectral lines assist in identifying various elements; for instance, the hydrogen emission spectrum displays distinct wavelengths.

This current atomic model is multifaceted and has several names.
Major advancement: understanding the electron as a duality of matter and energy.
- Due to rapid electron movement around the nucleus, precise locations of electrons cannot be directly determined.
The concept of uncertainty:
- Introduced the Uncertainty Principle, which influenced the terminology shift from orbitals to electron clouds.
- Clouds represent a distribution model, indicating probabilities of finding electrons in certain regions, rather than definitive locations.
- Certain areas in these clouds exhibit higher probabilities of locating electrons than others, demonstrating the complexity of electron behavior.