Light and Quantized Energy Electrons in Atoms

Thompson Plumb Pudding model of the atom Electrons stuck into a lump of positively charged material, similar to raisins stuck in dough.

Rutherford Proposed that atoms contained a dense positive nucleus surrounded by electrons Thought the atom was mostly empty space

Bohr Electrons are arranged in concentric circular paths (orbits) around the nucleus Called the planetary model Electrons have particular paths with fixed energy, which he called its energy level

Energy level region around the nucleus where the electron is likely to be moving electrons can “jump” from one energy level to another Quantum the amount of energy required to move an electron from its present energy level to the next higher energy level

Locations of Electrons in an Atom Atomic orbital the region in space where the electron is likely to be found Locations of Electrons in an Atom Electrons can be described by a series of four quantum numbers

Principal quantum number (n) Quantum Numbers Principal quantum number (n) Describes the principal energy level an electron occupies and relative size It has values of 1,2,3,4… As n increases the orbital becomes larger, the electrons spend more time farther from the nucleus and the atom’s energy increases.

Bohr Model

Energy Levels The first energy level represents the ground state. In the ground state the atom does not radiate energy. The electron moves to a higher energy orbit (energy level) when it absorbs Energy. The electron moves to a lower orbit and emits a quantum of energy (as a certain frequency/color of light)

Atomic Line Spectra (Emission Spectra) Elements in the gas phase emit light when hooked up to a voltage source. Only certain wavelengths of light are emitted The wavelength must then be passed through a prism to separate the lines Every element has a unique line spectrum The “fingerprint” of an element Can be used to identify unknown elements The emission spectrum of a substance can be seen by energizing a sample of material either with thermal energy of with some other form of energy (such as a high-voltage electrical discharge tube for gaseous substances)

Atomic Emission Spectra Light in a neon sign is produced when electricity is passed through a tube filled with neon gas. The neon atoms become excited. The excited atoms return to their stable state by emitting light to release energy.

Atomic Emission Spectra A white-light spectrum is continuous, with some radiation emitted at every wavelength. The emission spectrum of an individual element includes only certain specific wavelengths.

Atomic Emission Spectra The atomic emission spectrum of an element is the set of frequencies of the electromagnetic waves emitted by the atoms of the element. The energy of the photon being released corresponds to different wavelengths of light. A higher energy photon might be blue in color while a lower energy photon might be red in color.

Atomic Emission Spectra Each element’s atomic emission spectrum is unique.