Question

Explain generally the development of the modern picture of the atom – include the contributions from Dalton’s atomic theory, Nuclear Theory, the empirical data from the Balmer-Rydberg equation, the Bohr Model, and quantum mechanics.

Give an overview of quantum mechanics. Include the concepts of the wave function and each of the four quantum numbers.

Explain how polarity and dipole moment relate to the concept of the intermolecular attractions in substances. Compare and contrast attractive forces of hydrogen bonding, dipole-dipole interactions, and London dispersion forces. Your answer should be more in depth than just defining the three terms.

Answer 1

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Neils Bohr Atomic Theory

• Rutherford’s model did not explain how electrons were arranged in the atom

• Bohr experimented on electron arrangement using the spectra of elements (hydrogen in particular)

• His observations: – White light (sunlight) consists of a continuous spectrum (all colours or frequencies of visible light are present) – When electricity passes through a gaseous element at low pressure, light of a characteristic colour is given off (Ne=red) – If this light passes through a prism (crystal), a series of coloured lines appear between black spaces – Called a line spectrum

Bohr’s Proposal for Atomic Structure

1. Based on hydrogen atom, electron found in certain allowed areas. – These areas have definite fixed level of energy 2. Each energy level corresponds to an orbit (path around nucleus) where electron can move – First orbit = smallest radius – 2 nd orbit = larger radius 3. Electron can travel in its allowed orbit indefinitely – There is no loss of energy and atom will not collapse 4. Electron can change energy levels ONLY by gaining a specific amount of energy (quanta) – Electron must “jump” from one level to the next, not halfway – Quantity of energy needed for jump = difference in energy between energy levels .

quantum mechanics

The quantum mech

anical model is based on quantum theory, which says matter also has properties associated with waves. According to quantum theory, it’s impossible to know the exact position and momentum of an electron at the same time. This is known as the Uncertainty Principle.

The quantum mechanical model of the atom uses complex shapes of orbitals(sometimes called electron clouds), volumes of space in which there is likely to be an electron. So, this model is based on probability rather than certainty.

Four numbers, called quantum numbers, were introduced to describe the characteristics of electrons and their orbitals:

• Principal quantum number: n

• Angular momentum quantum number: l

• Magnetic quantum number:

  

• Spin quantum number: