 # Chapter 4 Arrangement of Electrons in Atoms 4.1 The Development of a New Atomic Model.

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Chapter 4 Arrangement of Electrons in Atoms 4.1 The Development of a New Atomic Model

Properties of Light Electromagnetic Radiation: EM radiation are forms of energy which move through space as waves There are many different types of EM waves visible light x-rays ultraviolet light infrared light radio waves Waves: Not Just For The Beach Anymore!

EM Waves Move at speed of light: 3.00 x 10 8 m/s Speed is equal to the frequency times the wavelength c = v Frequency (v) is the number of waves passing a given point in one second Wavelength ( ) is the distance between peaks of adjacent waves Speed of light is a constant, so v is also a constant; v and must be inversely proportional

Light and Energy: The Photoelectric Effect Electrons are emitted from a metal when light shines on the metal Incoming EM radiation from the left ejects electrons, depicted as flying off to the right, from a substance. Radiant energy is transferred in units (or quanta) of energy called photons (Max Planck)

p+p+ nono e-e- Photoelectric Effect When a specific or quantized amount of energy is exposed to the atom, the electron jumps from its “ground” or original state to an “excited” state energy absorption spectrum ground state e -

p+p+ nono e-e- Photoelectric Effect When the “excited” electron returns to lower energy levels, it releases energy in the form of light energy photon emission spectrum! travels at the speed of light (3.00 x 10 8 m/s) excited state e -

A photon is a particle of energy having a rest mass of zero and carrying a quantum of energy A quantum is the minimum amount of energy that can be lost or gained by an atom Energy of a photon is directly proportional to the frequency of radiation E = hv (h is Planck’s constant, 6.62554 x 10 -24 J * sec)

Electromagnetic Spectrum Wavelength increases→ Frequency decreases→ Energy decreases→

Electromagnetic Spectrum

Electrons as Waves and Particles Electrons have wavelike properties Consider the electron as a wave confined to a space that can have only certain frequencies

Wave-Particle Duality Energy travels through space as waves, but can be thought of as a stream of particles (Einstein) Each particle has 1 quantum of energy.

Line Spectrums Ground State:The lowest energy state of an atom Excited State:A state in which an atom has a higher potential energy than in its ground state example: Neon lights

Emissions Spectrum Bright line spectrum: Light is given off by excited atoms as they return to lower energy states Light is given off in very definite wavelengths A spectroscope reveals lines of particular colors- light passed through a prism; specific frequencies given off.

The Hydrogen Line Spectrum Definite frequency Definite wavelength http://student.fizika.org/~nnctc/spectra.htm

p+p+ nono e-e- Niels Bohr Bohr Model Energy levels Electrons circle around the nucleus on their energy level

The Bohr Model of the Atom Electron Orbits, or Energy Levels Electrons can circle the nucleus only in allowed paths or orbits The energy of the electron is greater when it is in orbits farther from the nucleus The atom achieves the ground state when atoms occupy the closest possible positions around the nucleus Electromagnetic radiation is emitted when electrons move closer to the nucleus.

The Bohr Atomic Model

Energy transitions Energies of atoms are fixed and definite quantities Energy transitions occur in jumps of discrete amounts of energy Electrons only lose energy when they move to a lower energy state

Shortcomings of the Bohr Model Doesn't work for atoms larger than hydrogen (more than one electron) Doesn't explain chemical behavior

Quantum Model of the Atom

The Heisenberg Uncertainty Principle Werner Heisenberg- 1927 "It is impossible to determine simultaneously both the position and velocity of an electron or any other particle.”

Quantum Theory Quantum theory describes mathematically the wave properties of electrons and other very small particles Electrons do not move around the nucleus in "planetary orbits" ????????

specify the properties of atomic orbitals and the properties of the electrons in orbitals: Principal Quantum Number (n) Angular Momentum Quantum Number (l) (shape : s,p,d,f) Magnetic Quantum Number (m) Spin Quantum Number Quantum Numbers

p+p+ nono e-e- Energy levels, n n = 1 n = 2 n = 3 n = 4 Indicates the main energy levels occupied by the electron Principal Quantum Number (n)

Angular Momentum Quantum Number (l) Indicates the shape of the orbital Shapes are designated s, p, d, f S shape is spherical P shape is a dumbbell, or figure 8 Click Here! Click Here!

Magnetic Quantum Number (m) The orientation of the orbital around the nucleus Spin Quantum Number Indicates the fundamental spin states of an electron in an orbital A single orbital can contain only two electrons, which must have opposite spins

Diagrams of the Orbitals

Writing Electron Configurations Rules: Aufbau Principle An electron occupies the lowest-energy orbital that can receive it Hund's Rule Orbitals of equal energy are each occupied by one electron before any orbital is occupied by a second electron, and all electrons in singly occupied orbitals must have the same spin Pauli Exclusion Principle No two electrons in the same atom can have the same set of four quantum numbers

Writing Electron Configurations Hund's Rule Orbitals of equal energy are each occupied by one electron before any orbital is occupied by a second electron, and all electrons in singly occupied orbitals must have the same spin 1 st e-2 nd e- 3 rd e-4 th e-

Configuration Notation (2 of 3) The number of electrons in a sublevel is indicated by adding a superscript to the sublevel designation Hydrogen = 1s 1 Helium = 1s 2 Lithium = 1s 2 2s 1 Aufbau Principle An electron occupies the lowest-energy orbital that can receive it (Always start with n = 1 and work your way up)

Orbital Filling Order 1s 2s2p 3s 3p3d 4s 4p4d 4f 5s 5p5d5f 6s6p 6d 7s7p START FINISH

Noble Gas Notation (3 of 3) The configuration begins with the preceding noble gas’s symbol in brackets and is followed by the rest of the configuration for the particular element. [Ne] 3s 2 3p 5

Terms Highest occupied energy level: The electron containing energy level with the highest principal quantum number Inner shell electrons: Electrons that are not in the highest energy level Octet Rule: Highest energy level s and p electrons are filled (8 electrons)

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