Physics and the Quantum Mechanical Model Scientist’s observed certain elements emit a visible light when heated in a flame and discovered an element’s chemical behavior is related to the arrangement of electrons in its atoms. Light can act as both a wave and a particle.

The Electromagnetic Spectrum Electromagnetic radiation is a form of energy that acts like a wave as it travels through space. All electromagnetic waves (including visible light) travel at a speed of 3.00 x 10⁸ m/s in a vacuum.

Wave Nature of Light All waves can be described by: wavelength, frequency, amplitude, and speed. The speed of light(ϲ) is a universal value and can be calculated by multiplying wavelength(λ) and frequency(ν): ϲ = λ x ν or ϲ = λν

All electromagnetic waves have the same speed, but they have different wavelengths and frequencies. Wavelength and frequency are inversely related: meaning as one increases the other decreases. The electromagnetic spectrum contains all forms of electromagnetic radiation. Energy increases as frequency increases.

Sunlight is considered white light and contains all ranges of wavelengths and frequencies. When it passes through a prism it is separated into all the colors of the visible spectrum.

Atomic Emission Spectra When atoms absorb energy, electrons move into higher energy levels. These electrons then lose energy by emitting light when they return to lower energy levels. When the electron has its lowest possible energy, the atom is in its ground state. Specific elements emit specific colors (specific frequencies of light) when their atoms are excited and release energy to become stable. The atomic emission spectrum of an element is the set of frequencies of the electromagnetic waves emitted by atoms of the element. The atomic emission spectrum of an element is the color of light that is emitted when the atom of that element releases energy. (example is neon signs) This can be used to identify many elements using a flame test.

Quantum Mechanics Classical mechanics describes the motions of bodies much larger than atoms, while quantum mechanics describes the motions of subatomic particles and atoms as waves. The Heisenberg uncertainty principle states that it is impossible to know exactly both the velocity and the position of a particle at the same time. Einstein proposed that light has both wave and particle characteristics. So a beam of light can be thought of as both a wave and a stream of particles called photons (which have no mass and carry a quantum of energy).