# Chemistry Wavelength

As a person in science, i should know the order of colours in the visible spectrum and the span of visible wavelengths. Question: if light is a ..

Answer: max planck proposed that e.m radiation comes in units of defined energy rather than in any arbitrary quantities. Planck called it quantum

The Photoelectric Effect

Planck’s theories were used to explain a number of observations that had been troubling scientists.

Einstein extended Planck’s ideas and suggested that each quanta of light behaves as a tiny particle called a __photon_ which has an energy E = h 1) it is said to be in an Excited state

Finally, explaining the line spectrum:

Bohr completed is model by making one more grand conclusion. He said that the electron could “jump” from one orbit to another by either emitting or absorbing photons with specific frequencies. Thus:

• To move to a higher energy orbit ( a greater value of n) an electron must Absorb energy

• To move to a lower energy orbit ( a lower value of n) an electron must Emit energy

• The frequency of the absorbed or emitted energy corresponds to the energy difference between orbits,

• Relationships between orbits:

Concept check- how do u calcuate the energy difference between orbits? What is the physical meaning of calculating the energy required to promote an electron from m=1, n= infinity The greater the energy the smaller the wavelength

de Broglie used the term matter waves to describe the wave-like properties of matter.

With the regards to the atom, de Broglie concluded that an electron orbiting a nucleus could be thought of as a wave possessing a characteristic wavelength. Example. Calculate the wavelengths of the following objects. (a) a baseball weighing 142 g thrown at 142 km/h. (b) a helium atom moving at a speed of 8.5 x 105 m/s. The importance of the above example......

CH 5-2-3

The Uncertainty Principle

The dual nature of matter (particles and waves) creates some difficulties with regards to the location of an electron is space.

The problem lies with the fact that a wave extends in space and defining its location cannot be done. Since an electron (or some other small particle) has wave properties then we cannot locate it at some specific time.

Heisenberg’s Uncertainty Principle: on the mass scale of atomic particles, the exact position, direction of motion, and speed cannot be determined simutltaneously. Heisenberg further showed that the product of the uncertainty in position and uncertainty in momentum is related to Planck’s constant: Quantum Mechanics and Atomic Orbitals

In 1926, Schrödinger, set out the general equations describing the motion of electrons in terms of waves and particles. The equations are complex and are beyond the scope of this class. However, the solutions of the Schrödinger equations are importance to us.

• Solving Schrodinger’s equation leads to a series of mathematical functions Called wave function(also called orbitals) that

are usually represented by the symbol R.

• The wave function gives no information about the path of the electron. It provides a mathematical description of the electron’s matter-wave in terms of position in three dimensions.

• The square of the wave function (_R _2 ) gives the probability of finding the electron at any point in space.

• By finding probabilities at various points in space about the nucleus it is possible to construct an electron density mass

Important note: the orbit in Bohr’s model (which is defined by the value of n) is different from the orbital in the quantum mechanical model. Orbitals and Quantum Numbers

• Three quantities (_n, l, _m l ) called quantum numbers are involved in the wave equations. Each quantum number can have many integral values and each set affords one solution to the wave equation.

• A specific set of values...

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