The Arrangement of Electrons in Atoms The Development of the New Atomic Model

What is wrong with this model??

New atomic model needed… Rutherford’s model was an improvement over previous models but... Rutherford’s model was an improvement over previous models but... Failed to explain why the electron did not spiral into the nucleus (remember opposite charges attract). Failed to explain why the electron did not spiral into the nucleus (remember opposite charges attract).

The new atomic model will explain why this happens! But first we need to talk about light and its properties.

The Dual Nature of Light Before 1900, scientists thought light behaved solely as a wave. Before 1900, scientists thought light behaved solely as a wave. However scientist found in some experiments that light behaved like a beam of particles. However scientist found in some experiments that light behaved like a beam of particles. We now know that light has particle-like characteristics as well. We now know that light has particle-like characteristics as well. Some properties are best explained by light’s wave nature other properties by it’s particle nature. Some properties are best explained by light’s wave nature other properties by it’s particle nature.

Wave Characteristics

Electromagnetic Radiation Includes visible light, x-rays, ultraviolet, infrared light, microwaves and radio waves. Includes visible light, x-rays, ultraviolet, infrared light, microwaves and radio waves. Take a look in the back corner of the room. Take a look in the back corner of the room. Exhibits wave like behavior. Exhibits wave like behavior. Is related to _________ and __________. What does the name suggest? Is related to _________ and __________. What does the name suggest?

Electromagnetic Spectrum

Wave Diagram

Wave Characteristics Wavelength- Wavelength- The distance between two consecutive peaks or troughs. Frequency- Frequency- The number of waves that pass a point each second (the unit is the Hertz, Hz). One complete wave or cycle per. second = 1 Hz. Velocity- Velocity- Distance a peak moves in a unit of time. Distance a peak moves in a unit of time.

It’s Slinky, It’s Slinky

c = f c = f velocity = frequency x wavelength velocity = frequency x wavelength The speed (velocity) of electromagnetic waves is constant (c). The speed (velocity) of electromagnetic waves is constant (c). C = 3.0 x 10 8 m/s If you know the frequency you can calculate the wavelength and… If you know the frequency you can calculate the wavelength and… SO WHAT DOES ALL THIS HAVE TO WITH A NEW ATOMIC MODEL?? SO WHAT DOES ALL THIS HAVE TO WITH A NEW ATOMIC MODEL??

Why do we need to learn about this???

We are getting to that…It will take some time though. It took the best minds in science years to explain …it should take us at least a few classes…so do not worry if it does not come easy.

An understanding of the arrangement of electrons in an atom makes it possible to explain/predict the chemistry of the elements…in other words, it will make the rest of the course much easier… An understanding of the arrangement of electrons in an atom makes it possible to explain/predict the chemistry of the elements…in other words, it will make the rest of the course much easier… SO… SO…

HW: complete the section 4-1 and properties of light ppt worksheet. HW: complete the section 4-1 and properties of light ppt worksheet. This will be collected. This will be collected.

Let’s Try Some Calculations c = f c = f Calculate the frequency of ultraviolet light that has a wavelength of 1 x meters. Calculate the frequency of ultraviolet light that has a wavelength of 1 x meters. Calculate the wavelength of a light that has a frequency of 4.62 x Hz. Calculate the wavelength of a light that has a frequency of 4.62 x Hz. For the 2 nd example, what visible characteristic of light is related to wavelength? For the 2 nd example, what visible characteristic of light is related to wavelength?

DIFFERENT COLORS Each different color has a different wavelength. Each different color has a different wavelength. How does electromagnetic radiation with a short wavelength effect you? How does electromagnetic radiation with a short wavelength effect you? How does electromagnetic radiation with a long wavelength effect you? How does electromagnetic radiation with a long wavelength effect you? review the spectrum…

How are wavelength, frequency and energy related??? …as the length of the wave decreases the frequency_______________ and the energy ____________. Remember: c = f

The particle nature of electromagnetic radiation (Waves)

Max Planck Showed that electromagnetic radiation was not produced continuously but emitted in small specific amounts. Showed that electromagnetic radiation was not produced continuously but emitted in small specific amounts. Quantum – small specific amount of energy Quantum – small specific amount of energy

Quantum The energy of a quantum is related to its frequency. The energy of a quantum is related to its frequency. E = h f Energy = Planck’s constant x frequency h = x j. s h = x j. s Planck’s equation shows us that higher frequency light  higher energy Planck’s equation shows us that higher frequency light  higher energy

Try this… Calculate the energy of a quantum of ultra violet light using the frequency you determined in the previous calculation. Calculate the energy of a quantum of ultra violet light using the frequency you determined in the previous calculation.

The Photoelectric Effect When light shines on certain metals an electric current is produced (electrons are emitted from the metal). When light shines on certain metals an electric current is produced (electrons are emitted from the metal). Only light of a certain minimum frequency can cause electrons to move. Only light of a certain minimum frequency can cause electrons to move. This could not be explained by the wave theory of light… This could not be explained by the wave theory of light…

Violet light produces photoelectric effect… red light does not produce photoelectric effect… Einstein explained this by proposing that light has a particle nature. High frequency light (violet) consists of ‘particles’ with a high energy low frequency light (red) consists of ‘particles’ with a low energy Particles of light are called photons…

Photoelectric Analogy High energy (violet) photons are like bowling balls. High energy (violet) photons are like bowling balls. Low energy (red) photons are like ping-pong balls. Low energy (red) photons are like ping-pong balls. If they both travel at the same velocity which is more energetic? If they both travel at the same velocity which is more energetic?

Homework – read pg answer questions 1-3 (pg 134), complete the first side of the wavelength calculation sheet Homework – read pg answer questions 1-3 (pg 134), complete the first side of the wavelength calculation sheet