Chapter 10

Matter and energy were thought to be distinct in the early 19th century.

Matter consisted of particles; whereas electromagnetic radiation (energy) consisted of waves.

Waves were considered mass-less and you did not know their position (unlike a particle).

Young’s Double Slit experiment proved that light travels in waves.

• This includes radio waves, microwaves, visible light, X-rays, gamma rays

• Energy travels through space by way of electromagnetic radiation.

There is a direct relationship between the frequency of a wave and the energy associated with the radiation. (Radio waves are low energy and X-Rays are high energy.)

In terms of visible light (ROYGBIV); red is low energy and violet is high energy.

particles of lightPhotons have mass in a relative sense. It

does not have rest mass, but mass like a moving object that has momentum (p). (p=m(mass)v(velocity))

If a photon strikes a particle (i.e. electron), the photon will displace the particle.

The fact that light shows both wave and particle properties is why it is said light has a dual nature.

Since light has particle nature, do particles have wave nature?

1. H atoms exist only in specified energy states

2. H atoms can only absorb certain amounts of energy, and no other

3. When excited H atoms lose energy, they lose only certain amounts of energy emitted as photons

4. The different photons given off by H atoms produce color lines seen in the bright line spectrum of Hydrogen

1. The greater the energy lost by the atom, the greater the energy of the photon.

2. More energy, closer to violet, than red

something exists only with or at specific energies.

When an electron is excited, it jumps to a higher energy level

When the electron goes back to its ground state, it releases a photon at a specific wavelength

Different colors are admitted depending on the distinct amount of energy released.

The bright line spectrum of excited hydrogen atoms is due to electrons falling from higher energy levels to lower energy levels (ground state).

Each element has its own specific bright line spectrum.

The Bohr model only worked for hydrogen for predicting the emission spectrum.

The Bohr model did not work for other elements that had more than one electron like hydrogen.

This brought about the Quantum Mechanical Model of the Atom.

The Quantum Mechanical Model is based on electrons traveling in a wave pattern. (diffraction pattern)

The pattern of the electrons is that of a standing wave in which the wave does not appear to move.

The path that the electron follows in the orbit around the nucleus must be some integer of the wavelength.

A combination of high mathematics (beyond the scope of this course) attempt to explain the position of an electron in the electron cloud became known as an orbital.

An orbital is not to be confused with the circular motion of the Bohr model.

An orbit is rather an area of highest probability to find the electron.

The detailed path of an electron is not known.